deliverable 4.5 report on “iron utilisation and toxic ... · d4.5 | page 1 a new mining concept...

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A new mining concept for extraction metals from deep ore deposits by

using biotechnology

Deliverable 4.5 Report on “Iron utilisation and toxic

elements removal”

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G.E.O.S. Ingenieurgesellschaft mbH

Cobre las Cruces, S.A.

Checked by: Approved by: Name: Checked Name: W Slabbert Date: 2018-07-20 Date: 2018-07-20

Signature: Include scanned signature Signature:

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D4.5 Report on “Excess iron utilization and toxic elements removal”

Due date of Deliverable 2018-07-31

Actual Submission Date 2018-07-31

Start Date of Project 2015-03-01

Duration 42 months

Deliverable Lead Contractor ClC

Revision Version 1.1

Last Modifications 2018-07-20

Nature Report

Dissemination level CO

Public Summary enclosed No

Reference / Workpackage 4.4, 4.5

Digital File Name De-180831-0047 - D4.5 Report on “Excess iron utilization and toxic elements removal”

Document reference number De-180831-0047

No of pages 101

Keywords leaching solution; iron removal; iron recovery; solvent extraction; precipitation; microbial oxidation; ion exchange

In bibliography, this report should be cited as follows:

n/a

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List of figures

Figure 1 - First draft flowsheet for removal of excess iron and toxic elements considering the reintroduction of the treated solution in the bioreactor .............................................................................................. 17

Figure 2 - Possible routes for downstream processing of PLS from sandstone ore leaching (provided by IMN) ............................................ 19

Figure 3 - Potential technologies for transformation of the obtained iron products ................................................................................................. 20

Figure 4 - Route 1 - Microbial oxidation of ferrous iron in PLS from counter current leaching ........................................................................ 23

Figure 5 - Route 2 - Microbial oxidation of ferrous iron in treated PLS from counter current leaching ................................................................ 25

Figure 6 - Route 3 - Microbial oxidation of ferrous iron in treated PLS from counter current leaching ................................................................ 26

Figure 7 - Test route for optimized process ........................................... 28

Figure 8 - Results of charcoal filtering test of PLS from sand ore leaching (10/2016, IMN) ...................................................................................... 29

Figure 9 - Ferrous iron and cell numbers during microbial Fe(II) oxidation of charcoal filtered PLS. Designations: IMN orig.: original IMN PLS without any treatment; Ex 1 and Ex 2: IMN PLS after Cu-SX and carbon-filtering with 37 mg/L TOC (Ex 1) and 8 mg/L TOC (Ex 2), respectively. .............................................................................................................. 30 Figure 10 - Ferrous iron and cell numbers during microbial Fe(II) oxidation of charcoal filtered PLS. Designations: IMN orig.: original IMN PLS without any treatment or addition; Ex 3 S, 4 Y and 5 SP: IMN PLS after Cu-SX and charcoal filtering with 2 mg/L TOC and different supplementations; sulfur ( Ex 3 S), yeast extract (Ex 4 Y) or trace element solution (Ex 5 SP), respectively. .............................................. 31

Figure 11 - Results of the 1st metal recovery experiment by application of the flow scheme in Figure 15, except for IX .......................................... 33

Figure 12 - Results of the 2nd metal recovery experiment by application of the flow scheme in Figure 15, except for IX. ..................................... 34

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Figure 13 - Results of the 2nd metal recovery experiment by application of the flow scheme in Figure 15, except for IX along the whole process route. ..................................................................................................... 36 Figure 14 - Results of IX-step (resin: Lewatit TP207) of the solution after final Fe-precipitation from the 2nd recovery experiment according to Figure 15. A) Metal concentration after distinct volume that passed the IX column. B) Metal mass bound on the IX resin after distinct volume that passed the IX column [mg] and total percentage of metal mass bound on the IX column after applying 1 L solution [%]. C) Total mass of divalent metal ions (Me2+) that bound on the IX resin after distinct volume that passed the IX column [mg] and percentage of Me2+ mass bound on the IX column after 1L of solution applied [%]. ...................................... 37

Figure 15 - Modified process scheme as result of optimisation used for validation work ....................................................................................... 39

Figure 16 - Composition of precipitates obtained in recovery experiments (only major compounds) ........................................................................ 40

Figure 17 - Amounts of Fe, SO4 dissolved in the solutions (full colour), amounts of Fe, S in the precipitates (pattern) and pH-value (circle) for different process steps of the first recovery experiment ........................ 42

Figure 18 - Suggested process routes for the treatment of leaching solutions and possible iron recovery ..................................................... 46

Figure 19 - Iron Pourbaix Diagram. ....................................................... 50

Figure 20 - Iron Removal in the jarosite process. .................................. 51

Figure 21 - Iron removal in the goethite process. .................................. 52

Figure 22 - Effect of the redox potential on the transformation of goethite to hematite. ............................................................................................ 53

Figure 23 - Iron removal in the hematite process. ................................. 54

Figure 24 - Iron Pourbaix Diagram ........................................................ 56

Figure 25 - Cell body (top and bottom). ................................................. 59

Figure 26 - Anodized aluminium cell holder with piston and high pressure gauge. ................................................................................................... 59 Figure 27 - Anodized aluminium cell holder with piston and high pressure gauge. ................................................................................................... 59 Figure 28 - Typical cell body assembly ................................................. 60

Figure 29 - Membrane lab scale flowsheet. .......................................... 62

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Figure 30 - SEPA lab scale plant. ......................................................... 63

Figure 31 - SEPA cell components, stainless steel cell body, top and bottom. .................................................................................................. 64

Figure 32 – Different filtering mechanisms. ........................................... 65

Figure 33 Percentage of transmission in SO4= and Mg2+. ..................... 69

Figure 34 Percentage of rejection in SO4= and Mg2+ ............................ 69

Figure 35 - Calcium Contour Plot. GE OSMONIC DL. .......................... 73

Figure 36 - Calcium Linear Model. GE OSMONIC DL. ......................... 73

Figure 37 - Calcium Diagram Parte, GE OSMONICS DL. ..................... 74

Figure 38 - Copper Contour Plot. GE OSMONIC DL. ........................... 74

Figure 39 - Copper Linear Model. GE OSMONICS DL. ........................ 75

Figure 40 - Copper Pareto Diagram. GE OSMONICS DL. .................... 75

Figure 41 - Iron Contour Plot. GE OSMONIC DL. ................................. 76

Figure 42 - Iron Linear Model. GE OSMONICS DL. .............................. 76

Figure 43 - Iron Pareto Diagram. GE OSMONICS DL. ......................... 77

Figure 44 - Manganese Contour Plot. GE OSMONIC DL. .................... 77

Figure 45 - Manganese Linear Model. GE OSMONICS DL. ................. 78

Figure 46 - Manganese Pareto Diagram. GE OSMONICS DL. ............. 78

Figure 47 - Zinc Contour Plot. GE OSMONICS DL. .............................. 79

Figure 48 - Zinc Linear Model. GE OSMONICS DL. ............................. 79

Figure 49 - Zinc Pareto Diagrama. GE OSMONONICS DL. ................. 80

Figure 50 - Calcium Contour Plot. TIPSET XN45.................................. 80

Figure 51 - Calcium Linear Model. TRIPSET XN45. ............................. 81

Figure 52 - Calcium Pareto Diagram. TRIPSET XN45. ......................... 81

Figure 53 - Copper Contour Plot. TRIPSET XN45. ............................... 82

Figure 54 - Copper Linear Model. TRIPSET XN45. .............................. 82

Figure 55 - Copper Pareto Diagram. TRIPSET XN45. .......................... 83

Figure 56 - Iron Contour Plot. TRIPSET XN45. ..................................... 83

Figure 57 - Iron Linear Model. TRIPSET XN45. .................................... 84

Figure 58 - Iron Pareto Diagram. TRIPSET XN45. ................................ 84

Figure 59 - Manganese Contour Plot. TRIPSET XN45. ........................ 85

Figure 60 - Manganese Linear Model. TRIPSET XN45. ....................... 85

Figure 61 - Manganese Pareto Diagram. TRIPSET XN45. ................... 86

Figure 62 - Zinc Contour Plot. TRIPSET XN45. .................................... 86

Figure 63 - Zinc Linear Model. TRIPSET XN45. ................................... 87

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Figure 64 - Zinc Pareto Diagram. TRIPSET XN45. ............................... 87

Figure 65 - Permeate Flow vs. Time Evolution. .................................... 92

Figure 66 Retentate Concentration Evolution vs. Time. ........................ 92


Figure 68 Permeate Concentration Evolution vs. Time. ........................ 93




Figure 72 Permeate Concentration Evolution vs. Time ......................... 96

Figure 73 Permeate Specific Flow vs. Time Evolution. ......................... 98




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List of tables

Table 1 Chemical analysis of elements in sandstone and shale ........... 21

Table 2 Composition of leaching solutions (PLS (03/2016)) obtained from IMN ................................................................................................ 22

Table 3 Route 1 - Composition of the solution after Cu extraction and pre-precipitation of As ........................................................................... 24

Table 4 Route 2 - Composition of solutions after Cu extraction and pre-precipitation of As .................................................................................. 25

Table 5 Route 3 - Composition of the solution after treatment steps .... 27

Table 6 Composition of PLS (10/2016) for testwork on optimisation of process route 2 ...................................................................................... 28

Table 7 Solution composition after final Fe-precipitation step (1st experiment). .......................................................................................... 33

Table 8 Solution composition after final Fe-precipitation step (2nd experiment). .......................................................................................... 34

Table 9 Final element concentrations in treated solutions and limit values set by EU legislation .............................................................................. 38

Table 10 Composition of solid precipitation and bio-oxidation residues for the process route SX/C/K/Ox/K ............................................................. 41

Table 11 Guide values for pollutants in raw meal corrective substances and clinker (BAFU 2015) ....................................................................... 44

Table 12 Examples of Ferric and Ferrous Iron Complexes ................... 49

Table 13 Initial and final iron concentration in solution of each test ...... 57

Table 14 Final iron concentration in solution without aeration ............... 57

Table 15 Operational parameters and technical specifications of the SEPA CF Cell. ....................................................................................... 58

Table 16 Components necessary to operate the SEPA CF Cell. .......... 61

Table 17 Different types of membranes used in the filtration tests. ....... 67

Table 18 Most commonly used applications of several membranes ..... 67

Table 19 Test conditions ................... Fehler! Textmarke nicht definiert. Table 20 Test parameters ..................................................................... 68

Table 21 DOE Conditions. ..................................................................... 70

Table 22 Factorial design 22. ................................................................. 70

Table 23 Design matrix ......................................................................... 71

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Table 24 Parameters results with GE Osmonics DL membrane ........... 72

Table 25 Parameter results with TriPSet XN45 membrane. .................. 72

Table 26 Testing conditions for Tripset XN45 membrane. .................... 88

Table 27 Testing conditions for Tripset XN45 membrane. .................... 88

Table 28 Parameters results with Tripset XN45 membrane. ................. 89

Table 29 Parameters results with Tripset XN45 membrane. ................. 89

Table 30 Conditions operation with Tripset S80 membrane. ................. 90

Table 31 Obtained results using Tripset S80 membrane. ..................... 90

Table 32 Obtained results using Tripset TS80 membrane. ................... 91

Table 33 Testing Parameters for GE O. Duracid membrane. ............... 94

Table 34 Analytical results of the final solution obtained in the test. ..... 94



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Executive summary

Introduction and Objective of this Deliverable

The BIOMOre project aims to develop a new mining concept for extracting metals from deep ore deposits using economic, sustainable and environmentally acceptable technologies. The objective of BIOMOre project is to develop new technological concepts for in situ recovery of copper via bioleaching and hydrofracturing, as well as to determine the most cost-effective technologies for metal separation and marketable product generation.

The in situ (bio)leaching operation generates solutions containing the valuable components, and apart from that, also high concentrations of iron and various other metals. For recirculation to the in situ bioreactor as well as the ex situ biooxidation reactor, impurities and toxic elements (such as arsenic (As) and cadmium (Cd) must be removed to support maintenance of pH, Fe content and Fe(II)/Fe(III)-ratio. These impurities are normally prevented from building up via the removal of a small part of the bioleaching solution. This small stream is commonly called a “bleed stream”, and it is normally taken after the unit operations that recover the main valuable metals in solution (where the stream is called “barren stream”). This bleed stream contains iron, impurities and toxic elements, and it must be treated for separation of its components. The iron content is recovered for re-use in the process or for generating saleable products. Arsenic (As) and cadmium (Cd) are regulated under EU Water Framework Directive and Cd is considered to be a priority hazardous substance and thus testwork on iron separation and its recovery in a saleable form are included in the BIOMOre project. The industrial application of bioleaching and hydrofracturing requires an economical operation which could be supported by the recovery of water from process or waste streams. Therefore, technologies and techniques for water balance improvements and industrial removal of iron are investigated.

This deliverable report summarises results of testwork on iron recovery and toxic element removal as well as technologies and techniques for water balance improvement, suitable for industrial scale.

Laboratory scale testwork on iron recovery and toxic element removal

The best results for the treatment of leaching solutions (leaching solution is commonly referred to as PLS) were obtained by following the process steps: solvent extraction for cupper removal (SX), followed by pre-precipitation (Fe(III), As, Pb), followed by microbial oxidation of the remaining Fe(II) to Fe(III), and finally by Fe-precipitation. The main outcome was a very pure Fe precipitate, and with the advantage that no additional pH adjustments had to be applied.

It was however found that microbial activity during biological ferrous iron oxidation was impaired by residual SX-organics in the PLS after pre-precipitation. So, after some pre-tests, an additional step of active charcoal filtering was included to remove residual organics from the PLS after solvent extraction. Through this filter step the total organic content (TOC) of the PLS after Cu-SX was reduced by up to 95 %.

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In the subsequent work, the filtered PLS solutions were tested for their applicability in microbial Fe(II) oxidation. A good applicability would mean that the bio-oxidation process with the filtered PLS proceeded as fast as with untreated PLS. Several approaches involving the same PLS after charcoal-filtering were immediately subjected to bio-oxidation without prior pre-precipitation. As a control and for comparison, each test series also included one approach with original (untreated) PLS. In a first test series, only sources of ammonia and organic carbon ((NH4)2SO4 and tryptic soy agar(TSA)) were added to all approaches as performed previously. However, this methodology was not successful, meaning that bio-oxidation of Fe(II) for the approaches with filtered PLS took far longer than in case of the control approach with untreated PLS. In a second similar test series the approaches with filtered PLS were additionally supplemented with sulfur, yeast extract or trace element solution, respectively. As a result, the approach with sulfur and the approach with trace element supplementation achieved a very fast Fe(II) bio-oxidation compared (even 1 d faster, respectively) to the control. Obviously, both sulfur and trace element solution served as essential substrate or additive for the microbial community, without which microbial growth was impossible but which previously were removed from the PLS (by SX or by charcoal filtering). The elements and compounds molybdenum / molybdate, boron / borate and/or sulfur / sulfides were identified as possible candidates which potentially could have been formerly removed by SX and/or carbon-filtering.

Further testwork was performed with a larger PLS volume for the validation of the whole process route and to produce sufficient amounts of pre-precipitate (Fe-As-Pb) and Fe-precipitate for analysis by means of which a potential utilisation of the Fe-product(s) was assessed.

At the end of the laboratory scale testwork two process routes can be proposed for the treatment of leaching solutions with a potential utilisation of iron. However, the evaluation of the laboratory results showed that it is necessary to adapt the process routes for iron recovery due to the following reasons:

The pre-precipitation of As is feasible but consumes a lot of iron at the beginning. Thus, for recovery of as much iron as possible as a high grade product an alternative method (e. g. As-adsorption) had to be tried.

The microbial oxidation of the ferrous iron after Cu solvent extraction was difficult due to the inhibition of the microbes by the residual concentrations of chemicals from the solvent extraction process present in the solution, thus requiring a further filtration step with active charcoal for the removal of remaining traces of organic chemicals. Since microbial nutrients are also removed with the charcoal filtration, they have to be added subsequently to enable an efficient microbiological process.

Altogether the tests have shown that iron products of a relatively high purity can be obtained from the PLS or barren solution in the biological oxidation step. These products are the basis for the transformation into marketable iron products. In

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contrast the precipitates from the first and second chemical precipitation step contain significant amounts of toxic elements, so that their utilisation is limited.

Testwork on technologies and techniques for water balance improvement

Information focused on industrial technologies to review the state-of-art applicable to BIOMOre project has been searched with regards to iron removal and recycling including water balance optimisation. Furthermore, CLC created a mass balance using METSIM software to determine the typical composition of main streams and effluents to be produced in BIOMOre project. For this purpose, the composition of sulfide minerals in sandstone layer (according to IMN’s data) was taken into account. This and other data formed the basic inputs for the METSIM software to estimate the concentration of copper and other main metals in PLS and consequently producing the proper raffinate after solvent extraction circuit simulation. The mass balance design included washing (acid-water), in situ (bio) leaching, solvent extraction, electrowinning processing and effluent treatment units.

With the abovementioned information a research plan on iron removal and recycling was performed with synthetic solutions. Lime-assisted neutralisation with air oxidation methodology was used to produce data on iron removal for the final solution. The obtained results support that the studied methodology is very efficient to remove iron using the process conditions expected on BIOMOre project.

CLC also worked on the design, assembling and testing of a laboratory-scale membrane cell prototype unit to study nanofiltration and reverse osmosis for effluent and water recycling for BIOMOre conditions. The results showed that membrane techniques are very valuable for the project to optimise the project water balance.

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Content

List of figures ............................................................................................................ 4 List of tables ............................................................................................................. 8 List of abbreviations .............................................. Fehler! Textmarke nicht definiert. List of annexes ....................................................... Fehler! Textmarke nicht definiert. Executive summary ................................................................................................ 10 Content .................................................................................................................... 13 1. Introduction: Background and objectives ................................................... 15 2. Iron recovery and toxic element removal .................................................... 16 2.1. Methodology ................................................................................................ 16 2.1.1. Laboratory scale testwork: Treatment of barren solutions and effluents .. 16 2.1.1.1. Preparatory work ..................................................................................... 17 2.1.1.2. Treatment procedures ............................................................................. 18 2.1.2. Transformation of the pure iron compound to a marketable form ............ 20 2.2. Results ......................................................................................................... 21 2.2.1. Laboratory scale testwork: Treatment of barren solutions and effluents .. 21 2.2.1.1. Preparatory work ..................................................................................... 21 2.2.1.2. Treatment of solutions and iron recovery: Process route 1 ...................... 23 2.2.1.3. Treatment of solutions and iron recovery: Process route 2 ...................... 24 2.2.1.4. Treatment of solutions and iron recovery: Process route 3 ...................... 26 2.2.2. Optimisation of iron recovery process ...................................................... 27 2.2.3. Validation of test results ........................................................................... 32 2.2.3.1. Experiments on optimized process route 2 .............................................. 32 2.2.3.2. Experiments on ion exchange for the removal of residual toxic elements 37 2.2.4. Transformation of the recovered iron compound to a marketable form ... 39 2.2.4.1. Evaluation of precipitates ......................................................................... 40 2.2.4.2. Assessment of further utilisation .............................................................. 42 2.3. Discussion ................................................................................................... 45 3. Technologies and techniques for water balance improvements, industrial

removal of iron ............................................................................................... 48 3.1. Objectives .................................................................................................... 48 3.2. Methodology ................................................................................................ 48 3.2.1. Iron removal/recycling .............................................................................. 48 3.2.1.1. State-of-the-art technologies for iron removal/recycling ........................... 48 3.2.1.2. Conclusions ............................................................................................. 57 3.2.2. Membrane cell lab scale plant ................................................................. 57 3.2.2.1. SEPA CF Cell Components ..................................................................... 59 3.2.2.2. SEPA CF Cell Assembly .......................................................................... 60 3.2.2.3. Basic Principles of Membrane Filtration ................................................... 64 3.2.2.4. Basic Principles of Crossflow Filtration .................................................... 66 3.2.2.5. Examples of different crossflow studies ................................................... 66 3.2.3. Membrane Development ......................................................................... 67 3.2.3.1. Types of membranes used ...................................................................... 67 3.3. Results ......................................................................................................... 68 3.3.1. Preliminary Membrane Tests: Magnesium Sulfate solution ..................... 68 3.3.2. Tests with Secondary Copper Raffinate .................................................. 70

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3.3.3. Concentration Test .................................................................................. 88 3.3.4. Tertiary Test: PLS stream from CLC ........................................................ 90 3.4. Discussion ................................................................................................. 100 Publication bibliography ...................................................................................... 101 Annex ...................................................................... Fehler! Textmarke nicht definiert.

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1. Introduction: Background and objectives

The overall BIOMOre objective is to develop new technological concepts for in situ recovery of metals from deep deposits using controlled stimulation of pre-existing fractures in combination with in situ bioleaching.

The concept of in situ metal recovery (also known as in situ leaching) is a successfully operating technology in many solution mining sites worldwide (e.g. Beverley Mine, South Australia). The key advantage of in situ leaching is its minimal environmental footprint and that it only recovers the actual metal by dissolution, and that it does not produce tailings which typically require multidecade post-mining remediation.

An important activity within the project is devoted to efficiently recover metal(s) and impurity removal downstream of the in situ bioleaching process. Solutions obtained after the above-mentioned process would contain high concentrations of dissolved iron and other impurities that would impair the process performance in the case they built up in the process solutions. In addition to that, the project has to deal efficiently with the water balance by means of fresh water use minimization. Both important tasks are considered in BIOMOre project as task 4.4 and task 4.5.

Task 4.4 is devoted to iron recovery and toxic element removal and is led by G.E.O.S.. The deliverable is a summary report section on iron utilisation and toxic elements removal. Task 4.5 led by CLC, comprises technologies and techniques for water balance improvements and industrial removal of iron.

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2. Iron recovery and toxic element removal

2.1. Methodology

The in situ (bio)leaching operation generates solutions containing valuable components in high concentrations, and also iron and various other metals. For recirculation to the in situ bioreactor as well as the ex situ biooxidation reactor a bleed stream is removed and treated to remove excess iron as well as toxic elements (As, Cd, Hg), to maintain support maintenance of pH, Fe content and Fe(II)/Fe(III)-ratio. Barren solutions and effluents after recovery of valuable metals contain significant amounts of toxic elements, especially Cd and As. Furthermore, As and Cd containing residues are generated. As and Cd are regulated under EU Water Framework Directive and Cd is considered as priority hazardous substances. Thus task 4.4 of the BIOMOre project aims at separation of excess iron as iron (oxy)hydroxy-sulphates or hydroxide and its recovery in a saleable form. Therefore, the most cost-effective unit operations were determined in a flowsheet for valuable metal separation and recovery into marketable products.

For the investigation of iron utilisation and toxic elements removal testwork was done on for the following process steps:

pre-precipitation of arsenic,

subsequent recovery of pure iron (oxy) hydroxy-sulphate, (e.g. Schwertmannite)

post-precipitation of toxic elements like Hg and Cd from barren solutions and effluents.

Next to this the transformation of the pure iron compound to a marketable form should be evaluated. Finally, the achieved results should be integrated into a sound precipitation and ion exchange technology for treatment of effluents after metal stripping to meet the limits of EU Water Framework Directive and national legislation, particularly regarding priority hazardous substances in laboratory scale, basic engineering, capital and operation costs for upscaling to industry scale.

2.1.1. Laboratory scale testwork: Treatment of barren solutions and effluents

In order to determine the most appropriate flowsheet for an efficient iron recovery and removal of toxic elements from barren solutions and effluents, it was necessary to study different arrangements of treatment steps. The proposed testwork had to evaluate if iron can be recovered as iron (oxy)hydroxy-sulphate or hydroxide from the solution and transformed into marketable iron products. Besides it should be proven if toxic elements (e.g. As, Cd) can be removed either during a pre-precipitation step or after iron recovery.

For the testwork on treatment of barren solutions, the following subtasks were carried out:

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1. Preparatory work: Analyses of raw material and initial solutions, development of a preliminary flowsheet as basis for the laboratory scale testwork,

2. Laboratory scale testwork to validate the planned process steps (pre-precipitation of arsenic, oxidation of residual iron, subsequent recovery of pure iron (oxy)hydroxy-sulphate, e.g. Schwertmannite)

3. Laboratory scale testwork for removal of residual toxic metals

2.1.1.1. Preparatory work

The raw materials sandstone and shale ores obtained from the Rudna mine were homogenized and geochemically analysed.

A first draft flowsheet was developed for the recovery of excess iron and toxic element removal. It was based on the assumption that the solution is reintroduced into the bioreactor (FIGB) after treatment.

Figure 1 - First draft flowsheet for removal of excess iron and toxic elements considering the reintroduction of the treated solution in the bioreactor

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As the objective of the underground testwork with the bioleaching pilot plant was to demonstrate the viability of fracturing and (bio)leaching, the underground testwork was restricted to bioleaching only, and did not include the rest of the flowsheet. The underground location is not really suitable for detailed chemical experiments either. So, due to the expenses to implement an underground downstream recovery process and the unsuitability of the underground location as a testing laboratory for downstream work, it was decided to perform the PLS testwork in controlled laboratories on surface and simulate the full flowsheet in the underground location. The simulation was created by separating a portion of the solution leaching out of the test reactor, when a certain Cu concentration was reached and replacing that with a solution of the correct composition after copper removal. This part of the solution would consist of water, sulfuric acid, and ferrous and ferric sulfate and was intended to be the initial solution for the laboratory testwork.

2.1.1.2. Treatment procedures

The testwork was carried out with leaching solutions from sandstone ore only according to the priority of sandstone bioleaching in the underground test reactor. As the installation of the pilot plant underground was very time-consuming due to the onerous certification process for underground Polish mines, real PLS solutions could not be produced in time. It was then decided that initial testwork was to be carried out with leaching solutions produced by IMN in a laboratory leaching procedure from bulk ore samples. The testwork for the treatment of the solution comprises three basic steps: solvent extraction, precipitation and microbial oxidation.

Solvent extraction

Solvent extraction is typically used on industrial scale for copper removal and was therefore also used for the removal of copper on small scale. The extraction was carried out in one step (Cu-SX) which was not optimized but similar to IMN testwork (with conditions of 25% LIX984N in Exxsol D100, O/A-ratio 1:1).

Precipitation

Iron precipitation was achieved by adding calcium carbonate under controlled conditions. This causes the pH to rise, which in turn causes the ferric iron to precipitate. In a first precipitation step, toxic elements were also removed thereby resulting in a contaminated precipitation product. For the removal and recovery of a relatively pure iron production a second precipitation step was applied after microbial oxidation.

Microbial oxidation

Microbial oxidation of ferrous iron to ferric iron was achieved with continuous aeration within a pH range of 1.5 to 2.0. For a successful and efficient process, inhibition factors must be avoided and surrounding conditions adapted to the specific requirements of the microorganisms.

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In order to find the most appropriate order of process steps resulting in a relatively pure iron (oxy)hydroxy-sulphate (which is the basis for the transformation into marketable iron products), testwork was carried out along three different routes:

1. Microbial Fe2+ oxidation > SX > pre-precipitation of As > iron precipitation and product recovery

2. SX > pre-precipitation of As > microbial Fe2+ oxidation > iron precipitation

3. Pre-precipitation of As > microbial iron oxidation > SX > iron precipitation and product recovery

The following process flowsheet (Figure 2) shows the three potential processing routes. The procedure of the testwork is explained in section “2.2 Results”, as the optimisation of the steps is based on the test results obtained. The process route, which achieves an optimal treatment of the solution, is then repeated with a larger volume in order to validate previous results and to generate a sufficient amount of residues for further investigations of iron recovery.

Figure 2 - Possible routes for downstream processing of PLS from sandstone ore leaching (provided by IMN)

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2.1.2. Transformation of the pure iron compound to a marketable form

Three potential technologies for transformation of the obtained iron product into a marketable form were considered:

via calcination, washing, wet grinding and spray drying to obtain Fe2O3 granules or iron oxide pigments (A similar process has been intensely studied and optimized by G.E.O.S. in the former FP7 project ProMine).

via mixing with a binding agent or compaction to produce adsorbents (This process was recently developed by G.E.O.S. and other partners within national research projects).

by treatment in an autoclave to form hematite.

An overview of treatment possibilities for the transformation is shown in Figure 3.

Figure 3 - Potential technologies for transformation of the obtained iron products

As the overview in Figure 3 shows, there are at least three processing options for the iron precipitates produced in the treatment of leaching solutions, each leading to a different product and application: Fe2O3 granules for furnace processes in iron industry, adsorbent materials for water (As, PO4

3- and other oxy anions) and biogas treatment (H2S removal), hematite as a supplement in various industries (e.g. pigment).

The growing industrial production in China and other countries and the related rising demand for iron resources are increasing raw material prices and thus the steel

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furnace industry's interest in alternative iron resources. The Fe2O3 granules produced from precipitates obtained by treatment of leaching solutions could therefore be an alternative resource. Furthermore, current market research (by G.E.O.S.) showed that there is a demand for low cost iron based adsorbents especially in Asia and South America. Thus, the removal of iron from leaching solutions and transformation into a low cost adsorbent seems to be a very promising possibility to increase the revenue from the leaching operation by reducing the costs of the downstream process. The autoclave treatment of jarosite or schwertmannite at a temperature > 220°C to form hematite and acid is described in the literature (Bigham et al. 1990; Bigham et al. 1994; Cornell and Schwertmann 2003). The produced sulfuric acid could be used to reduce the acid requirement during pre-leaching and bioleaching whereas hematite can be used for pigment production, heavy media separation, radiation shielding or as a ballast polishing compound. The use of a capital-intensive piece of equipment such as an autoclave, combined with operating costs of the heating and cooling processes make the economics of this technical solution attractive only under a very special set of conditions. The feasibility of the different processes will be evaluated based on the quality of the recovered iron compounds.

2.2. Results

2.2.1. Laboratory scale testwork: Treatment of barren solutions and effluents

2.2.1.1. Preparatory work

The analysis results for the homogenized sandstone and shale sample are given in the Table 1.

Table 1 Chemical analysis of elements in sandstone and shale

Element [%]

Al Ca Fe K Mg Na S Ti

sandstone 1.14 1.47 0.85 0.40 0.33 0.37 0.83 0.07shale 4.07 11.85 1.56 0.60 2.08 0.28 2.55 0.18

Element [ppm]

Ag As Ba Cd Co Cr Cu Ga Zn V

sandstone 65 50 870 <10 30 20 2230 <50 <20 20shale 154 <50 140 <10 100 140 31600 <50 420 1040

Element [ppm]

Mn Mo Ni P Pb Sb Sc Sr U W

sandstone 790 70 30 170 290 <50 <10 70 <50 <50shale 1620 240 230 400 47300 <50 10 170 <50 <50

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The evaluation of the laboratory results from geochemical analyses of the sandstone and shale revealed that leaching solutions are expected to contain only low concentrations of toxic elements. The percentage of iron in the sandstone is low as well but iron will be enriched in the leaching solution during the leaching process.

As the installation and commissioning of the pilot plant at Rudna mine went on for longer than expected, the entire testwork was carried out with leaching solutions prepared by IMN with bulk samples sandstone ore from Rudna mine. The first leaching solutions obtained from IMN were produced by batch chemical leaching (with Fe2(SO4)3 and H2SO4), the later obtained solutions by counter-current-leaching. As expected the element concentrations in the solution from counter current leaching were higher compared to the batch chemical leaching solution (Table 2).

Table 2 Composition of leaching solutions (PLS (03/2016)) obtained from IMN

Element [ppm]

PLS (03/2016) from batch chemical

leaching

PLS (03/2016) from counter current

leaching Cu 1,400 3,700

Fe (total) 6,700 11,000Fe (II) 2,500 4,500

Al 18 43As 2.9 5.9Pb 4.2 6.3Ca 630 570Co 1.4 2.9Mg 250 630Mn 50 130Mo 0.57 1.6Ni 2.8 4.5Ag 0.003 0.057V 0.24 0.52Zn 1.7 3.5

Apart from the copper content in the leaching solutions the content of other valuable metals and toxic metals is rather low. The high iron concentration (6,700 or 11,000 ppm) in the solutions was caused by the addition of Fe2(SO4)3 during the leaching process. Since the in situ test operation also foresees the removal of a bleed stream with high iron concentration, the leaching solutions from IMN seemed to be appropriate to carry out the experimental tests.

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2.2.1.2. Treatment of solutions and iron recovery: Process route 1

Microbial Fe-oxidation pH-adjustment Copper solvent extraction pre-precipitation of As secondary precipitation of iron

The laboratory experiments along this process route were carried out with the PLS from counter current leaching. The microbial oxidation of ferrous iron prior to solvent extraction avoids the risk of any inhibition caused by the chemicals used in solvent extraction.

Under continuous aeration ferrous iron in the solution was microbially oxidised to ferric iron at pH 1.6 (Figure 4).

Figure 4 - Route 1 - Microbial oxidation of ferrous iron in PLS from counter current leaching

After adjustment of the pH copper was extracted using 25% (v/v) Lix984N in Exxsol D100 and a solution according to the composition displayed in Table 3 was obtained.

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Table 3 Route 1 - Composition of the solution after Cu extraction and pre-precipitation of As

Element [ppm]

Solution after Cu extraction

Cu extraction and titration to pH 2.8

Cu 135 115Fe (total) 11,000 900

Al 46.5 115As 6.5 0.48Pb 3.85 0.22Ca 495 700Co 2.9 2.55Mg 650 700Mn 140 125Mo 0.7 0.04Ni 4.75 4.15V 0.165 0.18Zn 4.3 4.35

The obtained solution was titrated with a calcium carbonate solution to pH 2.8. After separation and recovery of the precipitate chalk was added to the solution to adjust the pH to 4.5 to precipitate the residual iron. The performance of testwork showed that it is difficult to first pre-precipitate As in a low quality iron compound and subsequently recover a pure iron (oxy)hydroxy-sulphate (sulfate). Very careful pH adjustment is necessary to separate the contaminated from the relatively pure (oxy)hydroxy-sulphate. After increasing the pH to 2.8 in the first precipitation step more than 90% of the iron had already been precipitated. The product contained about 200 ppm As and 140 ppm Pb and is not pure enough for further processing. In contrast, the product from the second precipitation step was pure but with an insufficient quantity for a reasonable iron product recovery.


Copper solvent extraction pre-precipitation of As microbial iron oxidation secondary precipitation of iron

After Cu solvent extraction from the counter-current-leaching-solution using 25% (v/v) Lix984N in Exxsol D100 the solution was titrated with NaOH up to pH 2.9. Samples from different pH values during the titration were sent for analyses. The results (Table 4) showed that an increase of the solution’s pH to 2.9 led to a depletion of arsenic and other metals which precipitated along with ferric iron. However, the solution still contained iron as ferrous iron.

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Table 4 Route 2 - Composition of solutions after Cu extraction and pre-precipitation of As

Element [ppm]

Cu extraction Cu extraction and titration to pH 2.9

Cu 365 280 Fe (total) 11,500 4,000

Fe (II) 5,700 3,900 Al 50 92 As 6.5 0.018 Pb 3.75 0.41 Ca 500 600 Co 3.0 2.5 Mg 750 750 Mn 135 120 Mo 0.46 0.018 Ni 4.85 3.8 Ag 0.5 0.04 V 4.1 3.5

Subsequently, the titrated solution was inoculated with a mixed culture of iron oxidizing bacteria to oxidise the residual ferrous iron to ferric iron and precipitate the iron as (oxy)hydroxy-sulphate. Unfortunately, microbial iron oxidation proceeded very slowly. After a couple of weeks, the ferrous iron was totally transformed to ferric iron as it can be seen in Figure 5. The reason for this low oxidation rate seems to be the presence of residual chemicals from solvent extraction in the solution that inhibited the microbes.

Figure 5 - Route 2 - Microbial oxidation of ferrous iron in treated PLS from counter current leaching

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After the microbial oxidation chalk was added to the solution to gently elevate the pH to pH 4.5 and precipitate the ferric iron. The obtained iron compound was very pure with less than 2 ppm As and less than 50 ppm Pb. This product displayed excellent opportunities for further utilisation as adsorbent, but the total iron recovery was relatively low.


Pre-precipitation of As microbial iron oxidation pH adjustment copper extraction secondary precipitation of iron

The PLS from counter-current-leaching was titrated with 2.5 molar NaOH to a pH value of 2.8 to precipitate As together with some of the ferric iron (Table 5). The solution was inoculated with iron oxidizing bacteria (mixed culture) and after a couple of weeks ferrous iron concentration in the solution decreased to 1,800 mg/l (Figure 6). Due to the relatively high pH at the beginning of the oxidation step iron precipitated as iron (oxy)hydroxy-sulphate. The obtained product had a low As content of about 40-50 ppm but a relatively high lead content of 250 to 300 ppm. However, the quality would be sufficient to use the product for an adsorbent production.

Figure 6 - Route 3 - Microbial oxidation of ferrous iron in treated PLS from counter current leaching

After adjustment of the pH value to 1.5 copper was extracted using 25% (v/v) Lix984N in Exxsol D100. A solution with the following composition was obtained and 98% of the copper was extracted (Table 5). The solution obtained from copper extraction was used for a subsequent precipitation of the residual iron by calcium carbonate addition (gentle pH increase). However, the obtained product had relatively low iron content (5 – 10 %) and mainly consisted of gypsum. Thus, a utilisation of the second precipitation product seemed not economically feasible.

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After the second precipitation step the concentration of the toxic elements, like As, Pb, V, in the solution were below detection limit (<0.002 ppm).

Table 5 Route 3 - Composition of the solution after treatment steps

Element [ppm]

PLS (03/2016)

titration to pH 2.8

Cu extraction

titration to pH 4.6

Cu 3700 3,400 60 35 Fe (total) 11,000 8,400 2,650 1,600

Fe (II) 4,500 5,000 1,815 1,590 Al 43 38 50 4.6 As 5.9 1.3 0.7 <0.001 Pb 6.3 3.9 0.01 <0.001 Ca 570 530 550 490 Co 2.9 2.3 2.6 2.5 Mg 630 580 700 590 Mn 130 110 120 120 Mo 1.6 0.71 0.03 0.03 Ni 4.5 3.5 4.05 3.7 Ag 0.057 0.24 0.195 N/A V 0.52 2.7 4.15 <0.002

2.2.2. Optimisation of iron recovery process

As it can be seen in the previous section the best results for the treatment of the PLS were obtained by following process route 2 (Cu-SX pre-precipitation (partial Fe, As, Pb) bio-oxidation Fe-precipitation). The main outcomes were a very pure Fe precipitate and the advantage that no additional pH adjustments had to be applied. However, microbial activity during biological ferrous iron oxidation was impaired by residual SX-organics in the PLS after pre-precipitation. So, an additional active charcoal filtering step was included to remove residual organics from the PLS after solvent extraction. Laboratory testwork was performed with PLS (10/2016) generated by counter-current sandstone ore ferric-leaching conducted by IMN.

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Table 6 Composition of PLS (10/2016) for testwork on optimisation of process route 2

Figure 7 - Test route for optimized process

Element [ppm]

PLS (10/2016)

Cu 4800 Fe (total) 7700

Al 26 As 1.20 Pb 2.9 Ca 570 Co 2.30 Mg 620 Mn 120 Mo 3.0 Ni 3.9 Ag 0.13 V 0.4

An initial test was carried out with 1 L of PLS from sandstone ore leaching (10/2016, IMN, Table 6), which first was subjected to Cu-SX as performed previously and afterwards passed through a filter column (10 mL column volume) containing 6 g of active charcoal based on anthracite (AGF 1-3 100 AR, CarboTech, Germany). As a result, the TOC content, which was used to measure the residual organic concentration, could be clearly decreased from 210 mg/L to about 40 mg/L (Figure 8). This corresponds to a reduction of the TOC content by approx. 80 %.

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Figure 8 - Results of charcoal filtering test of PLS from sand ore leaching (10/2016, IMN)

Ongoing tests were conducted with bigger charcoal filter columns containing 30 g of anthracite charcoal (100 mL column volume), which allowed decreasing the TOC content of the PLS after Cu-SX by approx. 95 % (final TOC contents of about 8 or 2 mg/L at varying starting values of about 180 or 40 mg/L, respectively).

In the next step, the filtered solutions were tested for their applicability in microbial Fe(II) oxidation. A good applicability would mean that the bio-oxidation process with the filtered PLS proceeds as fast as with untreated PLS. The charcoal-filtered pregnant leach solutions (~37, 8 and 2 mg/L TOC) were immediately subjected to bio-oxidation without prior pre-precipitation. As a control and for comparison, one approach with original (untreated) PLS was carried out.

In the first test series (Figure 9), the solutions were supplemented only with sources of ammonia ((NH4)2SO4) and organic carbon (tryptic soy agar, TSA) to stimulate growth of the microbes. These additions happened in analogy to previous tests on microbial Fe(II) oxidation with IMN pregnant leach solutions which were part of the different processing routes initially studied.

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Figure 9 - Ferrous iron and cell numbers during microbial Fe(II) oxidation of charcoal filtered PLS. Designations: IMN orig.: original IMN PLS without any treatment; Ex 1 and Ex 2: IMN

PLS after Cu-SX and carbon-filtering with 37 mg/L TOC (Ex 1) and 8 mg/L TOC (Ex 2), respectively.

The results showed that microbial Fe(II) oxidation of the filtered PLS took place remarkably slower when compared to the untreated original PLS, for which ferrous iron was entirely bio-oxidised to ferric iron after 8 d (Figure 9). It was assumed that another substance essential for microbial growth was removed from the PLS along with residual SX organics by charcoal filtering. Because of that, a small amount of yeast extract (containing various essential substances such as trace elements, organic carbon, amino acids and traces of sulfides) was added to the solutions after 28 d of bio-oxidation. This effected an obvious acceleration of the microbial process for the approach with filtered PLS “Ex 2” which contained approx. 8 mg/L TOC. Biological Fe(II) oxidation of the approach “Ex 2” was finished after 43 d (15 d after yeast extract addition). However, it was still not possible to enhance bio-oxidation of the other approach “Ex 1” which perhaps contained still too much residual SX-organics of ~37 mg/L TOC after charcoal filtering. Microbial Fe(II) oxidation of “Ex 1” was not yet finished after 81 d and the test was aborted.

Another similar test series was performed with analogously treated IMN PLS (Cu-SX + charcoal filtering, 2 mg/L TOC) to study the influence of different supplementations on the bio-oxidation process (Figure 10). Sources of ammonia and organic carbon ((NH4)2SO4 and TSA) were added to all approaches as performed previously. The approaches with filtered PLS were additionally supplemented with sulfur (“Ex 3 S”), yeast extract (“Ex 4 Y”) or trace element solution (“Ex 5 SP”), respectively.

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Figure 10 - Ferrous iron and cell numbers during microbial Fe(II) oxidation of charcoal filtered PLS. Designations: IMN orig.: original IMN PLS without any treatment or addition; Ex

3 S, 4 Y and 5 SP: IMN PLS after Cu-SX and charcoal filtering with 2 mg/L TOC and different supplementations; sulfur ( Ex 3 S), yeast extract (Ex 4 Y) or trace element solution

(Ex 5 SP), respectively.

According to the results, biological Fe(II) oxidation of the approaches with additional sulfur (“Ex 3 Y”) and trace elements (“Ex 5 SP”) proceeded exceptionally fast and took only 4 d until complete Fe(II) oxidation (Figure 10). The process for both approaches proceeded even faster than for the original untreated PLS which took 5 d until Fe(II) was entirely depleted. Bio-oxidation of “Ex 4 Y” (yeast extract addition) was comparable in duration as for the last test series. It took 17 d until Fe(II) was totally oxidised.

Obviously, both sulfur and trace element solution served as essential substrate or additive for the microbial community, without which microbial growth was impossible but which previously were removed from the PLS (by SX or by charcoal filtering). By comparison of the elemental composition before and after SX it was noticed, that beside Cu a small amount of molybdenum (Mo) was co-extracted from the PLS. Mo is one of the trace elements (as molybdate) needed for growth of one or more members of the microbial community. Depletion or absence of Mo would hinder or prevent microbial growth. Another candidate may be boron (B), which is also an essential trace element (as borate) but was not analysed in the solutions. Furthermore, sulfidic components in the PLS are critical for microbial growth. Beside residual SX-organics also sulfides seem to be adsorbed by active charcoal and are filtered out of the PLS (e.g. active carbon is applied for hydrogen sulfide adsorption/filtering from gas streams). However, reduced inorganic sulfur components and/or sulfur serve as a substrate for one of the main members of the

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microbial community (Acidithiobacillus caldus). Depletion or absence of these substances would hinder or prevent microbial growth. It is assumed that supplementation of the two different additives lead to separate development of the microbial community, which was observed by microscopy. The sulfur supplemented approach showed a predominantly occurring single cell type while a more diverse microbial community was visible in the other approaches.

2.2.3. Validation of test results

2.2.3.1. Experiments on optimized process route 2

In the following experiments, a larger PLS volume was treated to investigate the whole process route 2 (Figure 2) and to validate results as well as to produce sufficient amounts of pre-precipitate (Fe-As-Pb) and Fe-precipitate for analysis by means of which a potential utilisation of the Fe-product(s) will be assessed. In the bio-oxidation step, sulfur supplementation was applied for microbial growth stimulation as it needs clearly less preparation and handling effort than supplementation of a quite complex trace element solution. In total, two such experiments were carried out. In the first one 2.5 L of PLS were treated, in the second one 3.7 L. The order of the processing steps (SX, carbon filtering, Fe pre-precipitation and main Fe-precipitation) was carried out as performed previously. In opposite to the previous experimental procedure, the first precipitation step as well as the second one was carried out with calcium carbonate for both recovery experiments to achieve a slightly increased pH value. For microbial Fe(II) oxidation the optimized conditions were used. The second recovery experiment served for testing reproducibility.

The recovery experiments carried out with 2.5 L (1st experiment) and 3.7 L of PLS (2nd experiment) lead to the precipitation residues listed in Table 10. The given concentrations refer to the dry mass of samples. The results of the analysed residues confirm the measured concentrations in the treated solutions.

The results of the first metal recovery experiment are shown in Figure 11 which displays the element separation based on the solution after final Fe-precipitation (Rec. SX/C/K/Ox./K) referring to element mass in original PLS. In addition, the composition of the solution after the final Fe-precipitation step is given in Table 7. The results of the second metal recovery experiment are presented in the same way in the following Figure 12 and Table 8.

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Table 7 Solution composition after final Fe-precipitation step

(1st experiment).

Figure 11 - Results of the 1st metal recovery experiment by application of the flow scheme in Figure 15, except for

IX

Element [ppm]

Rec. SX/C/K/Ox./K

Cu 73 Fe (total) 2.6

Ag <0.001 Al 2.1 As <0.001 Pb <0.001 Ca 580 Cd 2.4 Co 2.2 Cr <0.001 Hg <0.0001 Mg 610 Mn 120 Mo <0.001 Ni 3.5 U 0.015 V <0.002 W <0.001 Zn 3.3

The results indicate that most of the analysed elements could be separated by the proposed treatment scheme. Only several divalent metal cations (Me2+), namely Cd, Co, Mg, Mn, Ni and Zn were still present in the solution after final Fe-precipitation (Figure 11, Table 7, Table 8). This in particular is relevant for the aspect of toxic element removal. Some of the toxic elements which were present in the original PLS, like As, Pb, U were already removed from the solution by the precipitation steps. The respective solution concentrations after final Fe-precipitation were < 1 µg/L (As, Pb) and 1.5 µg/L or < 0.2 µg/L (U), respectively (Figure 12). The Hg concentration in this solution was also below the detection limit (< 0.1 µg/L). However, potentially toxic

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elements like Cd, Ni or Co are still present in the solution. So, a further separation step is needed, for which ion exchange (IX) was considered as a suitable technique.

Table 8 Solution composition after final Fe-precipitation step (2nd

experiment).

Figure 12 - Results of the 2nd metal recovery experiment by application of the flow scheme in Figure 15, except for IX.

Element [ppm]

Rec. SX/C/K/Ox./K

Cu 0.88Fe (total) 0.095

Ag <0.001Al <0.01As <0.001Pb <0.001Ca 584Cd 1.35Co 1.41Cr <0.001Mg 603Mn 114Mo <0.001Ni 1.7U <0.0002V <0.002W <0.001Zn 0.95

As can be seen from the results, percentage removal of elements is increased compared to the first recovery experiment and thus further optimisation of the removal was achieved when experiments were carried out with a higher volume of PLS. This can be due to the reduction of inaccuracies in laboratory and analytical procedures, as small-scale investigations can often be more sensitive. The composition of the solution after the final Fe-precipitation step is quite similar to the first recovery experiment and still contains the metal cations Cd, Co, Ni and Zn. Concentrations of the toxic elements As, Pb and U are < 1 µg/L (As, Pb) and <

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0.2 µg/L (U) respectively (Table 8) and are removed completely with the proposed process scheme.

An overview of the removal of elements along the whole process route is presented in Figure 13 for the results of the second recovery experiment. Element separation is given in [%] based on the solutions after SX (Rec. SX), carbon filtering (Rec. SX/C), pre-precipitation (Rec. SX/C/K), bio-oxidation (Rec. SX/C/K/Ox.) and final Fe-precipitation (Rec. SX/C/K/Ox./K), each referring to element mass in original PLS. Due to the implausibility of some analytical results, selected values are not considered in the graphic.

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Figure 13 - Results of the 2nd metal recovery experiment by application of the flow scheme in

Figure 15, except for IX along the whole process route.

The figure underlines the successful implementation of the selected sequence of process steps for toxic elements removal. Whereas the first process step of solvent extraction removes mainly Ag, Cu, Mo and W, the toxic elements As, Cd, Co, Cr, Ni, Pb, U, V and Zn are removed by subsequent stepwise precipitation of iron and the associated removal mechanisms.

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2.2.3.2. Experiments on ion exchange for the removal of residual toxic elements

With the solution resulting from the second Fe-precipitation step (2nd recovery experiment, 3.7 L results Figure 12, Figure 13), an ion exchange (IX) step was performed for the removal of further elements, in particular the toxic ones, still present in the solution after the second/ final Fe-precipitation step. The cation exchange resin Lewatit TP207 was used (Lanxess Germany), which is capable of binding divalent metal cations (Me2+), according to the following selectivity order: Cu2+ > V (VO2+) > U (UO2

2+) > Pb2+ > Ni2+ > Zn2+ > Cd2+ > Co2+ > Fe2+ > Be2+ > Mn2+ >> Ca2+ > Mg2+ > Sr2+ > Ba2+ >>> Na2+. A column test was performed using 20 g of IX resin and applying a total of 1000 mL solution (Figure 14 B) with a continuous flow of 100 mL/h. Analysis of the metals of interest took place after each 200 mL. The results are shown in Figure 14.

Figure 14 - Results of IX-step (resin: Lewatit TP207) of the solution after final Fe-precipitation from the 2nd recovery experiment according to Figure 15. A) Metal concentration

after distinct volume that passed the IX column. B) Metal mass bound on the IX resin after distinct volume that passed the IX column [mg] and total percentage of metal mass bound on the IX column after applying 1 L solution [%]. C) Total mass of divalent metal ions (Me2+) that bound on the IX resin after distinct volume that passed the IX column [mg] and percentage of

Me2+ mass bound on the IX column after 1L of solution applied [%].

As can be seen from the results all relevant Me2+ could be removed from the solution. The IX resin bound 100% of the originally containing masses of Cd, Co, Cu, Mn, Ni and Zn. The remaining concentrations in the last fraction of the flow through were < 0.2 µg/L Cd, 0.3 µg/L Co, 8 µg/L Cu, 3 µg/L Mn, 2 µg/L Ni and 1.5 µg/L Zn (Figure 14 A). The cations Ca2+ and Mg2+ were not fully bound to the IX resin, which is consistent with its rear position in the selectivity order of the IX resin. However, in

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total, about 90 % of the containing masses of Ca and Mg were bound to the IX-resin (Figure 14 B). The Ca and Mg concentrations in the flow through ranged between 600 and 900 mg/L (Figure 14 A). Both were not in the direct focus of the experiment and may be separated, if necessary, e.g. by an additional precipitation step (e.g. Mg removal is a work task of partner IMN). A total mass of 1.2 mg Me2+ was bound to 20 g of IX resin (ca. 59 mg/g IX resin), corresponding to a separation of 90 % of the containing Me2+ (Figure 14 C). Although Ca and Mg were not fully separated from the solution by the IX-resin, the capacity limit for the other Me2+ seemed not to be reached, as seen by the very low concentrations in the final flow through fraction (no breakthrough observed). In addition, an analogous test was performed with another IX resin (Purolite S930plus), which provided very similar results.

Assessment of finally achieved concentrations

The success of the toxic elements removal is assessed under consideration of the composition of treated solutions and the requirements of the EU Water Framework Directive. The directive itself does not contain limit values for hazardous substances in effluents of waste water treatment plants (WWTPs) but it requires the achievement and conservation of a good state of water bodies in terms of chemical and ecological aspects. Each member state has to implement rules and limit values in their national legislations to ensure the achievement of the overall European goals. Due to heterogenic national legislations there is no general limit value for hazardous substances in effluents of WWTPs. Thus, the assessment of the final composition of treated leaching solutions is done on the example of the German ordinance on waste water (so called “AbwV”). Table 9 below compares concentrations of elements in the final solution and limit values given by the German ordinance AbwV. Annex 39 and Annex 48 of this German ordinance list limit values which have to be attained before industrial waste water can be blended with other waste waters.

Table 9 Final element concentrations in treated solutions and limit values set by EU legislation

Element [ppm]

Rec. SX/C/K/Ox./K/IX

Limit values Germany

Cu 0.008 0.50 * Ag N/A1 0.10 * As N/A1 0.10 * Pb N/A1 0.50 * Cd < 0.0002 0.20 *,** Co 0.0003 1.00 * Cr N/A1 0.50 * Hg N/A1 0.05 *,** Ni 0.002 0.50 * Zn 0.015 2.00 *

* Limit values for discharged waters according to German AbwV Annex 39 (valid for effluents from non-metal production)

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** Limit values for discharged waters according to German AbwV Annex 48 (valid for the industrial use of selected hazardous substances)

1 Elements which were already found to be below the detection limit in the clear solution after the second precipitation step conducted previously were not analysed again after the final IX step as their concentrations were assumed to further decrease or at least to stay constant after IX-treatment

The results show that with the last treatment step (ion exchange) the limit values given by (German) law can be met and thus, the proposed treatment ensures a sustainable water management. The integration of the results into a sound precipitation and ion exchange technology for the treatment of effluents after metal stripping to meet requirements by law (EU Water Framework Directive and national legislation) leads to the following process scheme shown in Figure 15.

Figure 15 - Modified process scheme as result of optimisation used for validation work

2.2.4. Transformation of the recovered iron compound to a marketable form

From both recovery experiments the resulting solid Fe precipitates were analysed for their elemental composition (in particular Fe content and content of contaminants

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such as As, Pb) to prove the precipitates’ quality. The laboratory scale tests showed that iron can be recovered at relatively low pH (<5) from the PLS either as (oxy)hydroxy-sulphate (e.g. jarosite, Schwertmannite) or as goethite. Based on the analyses / quality information of precipitates (as described in the previous sections) the feasibility of three potential technologies for transformation of the obtained iron product(s) into a marketable form was evaluated.

2.2.4.1. Evaluation of precipitates

Quality of produced precipitates

The composition of the precipitation products from both recovery experiments is shown in Figure 16, which represents the major elements in bar charts.

Figure 16 - Composition of precipitates obtained in recovery experiments (only major compounds)

The results of the analysed residues for the first and second test series are given in Table 10.

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Table 10 Composition of solid precipitation and bio-oxidation residues for the process route SX/C/K/Ox/K

1st recovery experiment 2nd recovery experimentElement

[ppm] 1st

precipitation Bio-

oxidation 2nd

precipitation1st

precipitationBio-

oxidation 2nd

precipitation

Cu 300 370 4120 134.5 461 6380Fe 106000 196000 149000 104500 218000 119500Ag 0.0 0.0 0.0 0.1 0.1 0.0Al 800 <500 1700 600 100 1900As 60.0 <50 <50 61.8 4.7 4.6Pb 90.0 60 <20 64.4 32.1 1.0S 100000 100000 100000 100000 100000 100000

Ca 161000 73400 149000 159500 60900 158000Cd <10 <10 <10 2.7 2.7 64.5Co 10 <10 <10 2.7 2.6 55.7Cr 30 <10 40 12.0 6.0 39.0Mg 1600 600 1000 600 600 1300Mn 210 40 130 111 135 1040Mo 10 <10 <10 15.6 4.1 0.3Ni 10 <10 10 2.4 2.8 120U <50 <50 <50 0.3 0.2 8.3V <10 <10 <10 8.0 3.0 3.0W <50 <50 <50 1.7 1.2 0.2Zn 20 <20 20 8.0 5.0 133

Results confirm the measured concentrations in the treated solutions. The main compounds (shown cursive in Table 10) of the precipitate are iron (11-22 %), sulfur (10 %) and calcium (7-16 %). Regarding the results it becomes clear that the precipitates of the first and second precipitation step using calcium carbonate are composed quite similar as they are rich in Fe (around 11%), S (10 %) and Ca (16%). There are only two major differences: firstly, the concentration of toxic elements which is higher in the precipitate gained after the first precipitation step, and secondly, the Cu concentration which is higher in the precipitate of the second step. This proves that through pre-precipitation potentially hazardous substances such as As, Pb and Mo can be removed to obtain a really pure product without contaminants in the following process step (microbial oxidation). As expected, the residue obtained by microbial oxidation showed the highest Fe-concentration (20-22%) and the lowest Ca-concentration (6-7%) in the first and second experiment, due to the fact that no calcium carbonate was added. The second recovery experiment obtained final precipitation residues that contain significant concentrations of Cu, Cd, Co and Cr. The increasing Cu concentration in the precipitates after the last precipitation step corresponds to the observations for the treated leaching solution in which the last part of solved Cu is removed in the final process step (as shown in Figure 13).

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Quantity of produced precipitates

The evaluation of the produced quantities is done using the data from the first recovery experiment carried out with 2.5 L of leaching solution (results of the second recovery experiment are comparable and are therefore not described in this section of the deliverable report). The highest amount of precipitate was produced in the first precipitation step with in total 98 g, whereas the lowest amount was produced during microbial oxidation with in total 10 g. In the last step a total amount of 51 g was precipitated. Figure 17 shows the amounts of Fe and SO4

2- dissolved in the leaching solution, the amounts of Fe and S contained in the precipitates and the pH value. For the evaluation of the precipitates only the data of the starting solution (PLS), the first precipitation (SX/C/K), the microbial oxidation (SX/C/K/Ox) and the second precipitation (SX/C/K/Ox/K) are displayed.

Figure 17 - Amounts of Fe, SO4 dissolved in the solutions (full colour), amounts of Fe, S in the precipitates (pattern) and pH-value (circle) for different process steps of the first recovery

experiment

It can be seen that the total amount of Fe and SO42- dissolved in the solution

decreased with each process step and subsequently the amount of Fe and S in the precipitates increased. The addition of calcium carbonate and the subsequent increase in pH value in the first and second precipitation steps caused higher amounts of precipitates which cannot be found for the microbial oxidation stage performed at a lower pH value.

2.2.4.2. Assessment of further utilisation

Additional treatment steps for the transformation of recovered iron compounds into a marketable form will affect costs for the overall process. For this reason, a process scheme is needed that comprises as few steps as possible and achieves a valuable product with a wide range of applications.

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Formation of Fe2O3 granules

The treatment of residues to form Fe2O3 granules includes thermal calcination at 700-800 °C and further steps for washing, wet grinding and spray drying using a stabilizing agent. During thermal treatment, water and sulfur are removed from the residue resulting in an increased iron concentration. After treatment, the produced granules must fulfil the following properties required by metallurgical industries for further processing in a furnace process:

- dry material - Iron concentration above 60 % w/w - Phosphor concentration below 0.1 % w/w - Sulfur concentration below 1 % w/w.

Studies of (Wilck 2011) examined the possibilities of upgrading iron (oxy)hydroxy-sulphate for further utilisation. The raw material used was obtained from a pilot plant developed and operated by G.E.O.S. for microbial iron oxidation of acid mine drainage. Thermal treatment was investigated for the production of granules for the furnace process as well as for pigments for building materials and paints. The raw material contained 42 % w/w of iron and 5 % w/w of sulfur. Thermal treatment achieved iron concentrations above 60 % w/w and a complete removal of sulfate at 800 °C. As the results of the laboratory scale precipitation trials show, the iron content in the raw material is rather low at 10-20 % w/w. Even after the removal of the sulfur content during thermal treatment, iron concentrations of 60 % do not seem to be achievable.

From an economical point of view, energy consumption for the thermal treatment is also really high. Even though the process causes a release of sulfuric acid, which can be reused during leaching, quantities of iron precipitate produced are rather low. Therefore, the benefits of reusing sulfuric acid would not cover the expenses of thermal treatment and further process steps.

Formation of hematite

The transformation of iron (oxy)hydroxy-sulphate into hematite for further processing to pigments can be performed within one step by autoclave treatment. For the use of the iron based pigment as a colour additive for building materials, particular attention must be paid to the content of various pollutants. Several guide values are established limiting the content of pollutants in additive materials. Table 11 gives an overview of guide values set by the Suisse environmental agency BAFU (2015) for cement industry regarding the permitted content of pollutants in raw meal corrective substances as well as in clinker products.

In order to meet the requirements for building materials and to keep characteristics of the original material, dosage of pigments should be as low as possible. Thus, a high colour intensity of the product is required, which is achieved by a certain particle size as well as a sufficient iron content of the raw material. For high grade iron additives a Fe2O3 content of 90-100 % is recommended (Wilck 2011). However, testwork of

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(Wilck 2011) obtained successful results with particle sizes < 50µm and 66 % iron at a dosage of 3 % to the cement material.

Table 11 Guide values for pollutants in raw meal corrective substances and clinker (BAFU 2015)

Element [ppm]

Raw meal corrective substances

Clinker products

Cu 500 250As 30 15Pb 500 250Cd 5 5Co 250 125Cr 500 250Ni 500 250Zn 1000 750

A comparison of these guide values with the composition of the precipitates obtained shows that the concentrations of Cu meet limit values for raw meal corrective substances for residues obtained with the first precipitation step and microbial oxidation, but not for the residue of the second precipitation step. The concentrations of As correspond to the guide values for precipitation products obtained in the microbial oxidation and second precipitation steps, but not for the first. In contrast, Cd concentration is met for the first precipitation and microbial oxidation, but exceeds guide values within the second precipitation step. Pb, Co, Cr, Ni and Zn are below the guide values.

The precipitation residues produced in the first precipitation step and during microbial oxidation could meet the requirements for cement materials if As concentration gets reduced before precipitation (for instance by using a previous adsorption process). However, residues of the second precipitation step cannot be used, as the Cu concentration still exceeds the guide values. The last precipitation step results in the lowest quantity of precipitate. From this point of view, an utilisation of residues as pigments for building materials in cement industry seems to be conceivable.

Production of adsorbents

The production of adsorbents appears to be the most promising approach as no high temperatures are required resulting in lower operational costs. However, it should be noted that the production of adsorbents takes place in many process steps like moistening, dewatering, mixing, drying, crushing and sieving, which also entails high costs. The capacity of the adsorbent is based on the content of Schwertmannite (iron (oxy)hydroxy-sulphate) and thus the raw material must be rich in iron as well.

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Former studies of G.E.O.S. for the production of adsorbents were carried out successfully with a raw material obtained from the biological oxidation of acid mine drainage in a pilot plant which achieved precipitates with concentrations of 42 % Fe and 5 % S. With regard to the present values gained in the recovery experiments with at least 22 % Fe and 10 % S in the residues of the biological oxidation step it becomes clear that the quality of the products is not comparable with the composition of iron precipitates obtained with acid mine drainage. The iron concentrations of precipitates obtained in the precipitation steps with calcium carbonate are even lower in iron and higher in Ca concentration which is caused by the precipitation process itself. For the given example of Schwertmannite precipitate produced by microbial oxidation of acid mine drainage, a CaO concentration of 0.15 % w/w was measured whereas the precipitate obtained in the microbial oxidation step of the PLS contained 9 % w/w CaO.

From this it becomes clear that the application of microbial oxidation requires further process adaptions considering the composition of solutions to be treated. High concentrations of CaO and sulfate preferably react under formation of gypsum which makes up a large portion of the precipitate. Subsequently the iron content is relatively low. Even low-quality adsorbents such as FerroSorp (ironhydroxide) contain iron concentrations of at least 44.5 % w/w (HeGo Biotec 2015). Hence, it can be concluded that the quality of the produced precipitate is not sufficient for its application as an adsorbent.

2.3. Discussion

Results of the laboratory scale testwork have proven that a combination of solvent extraction, precipitation and ion exchange was successful for the removal of toxic elements. After the last treatment step there was no mentionable concentration of hazardous compounds detectable. Investigations with higher quantities of solution were performed along process route 2. The treatment was successful and verified previous results obtained with smaller volumes. Higher volumes of solutions allowed additional analyses of solid residues (precipitates), which confirmed results from water balances. Thus, it can be maintained that the chosen procedure is applicable and can be recommended for the treatment of the leaching solution.

However, the evaluation of the laboratory results showed that it is necessary to adapt the process routes for iron recovery out of the following reasons:

The pre-precipitation of As is feasible but consumes a lot of iron at the beginning. Furthermore, precipitation products of the microbial oxidation process were comparable low in iron but high in calcium (and sulfate) which is caused by precipitation process using calcium carbonate. Thus, for recovery of as much iron as possible as a high-grade product an alternative method (e. g. As-adsorption) is recommended.

The microbial oxidation of the ferrous iron after Cu solvent extraction was difficult due to the inhibition of the microbes by the residual concentrations

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of chemicals from the solvent extraction process present in the solution. That is why a further filtration step with active charcoal is needed for the removal of remaining residues. Since nutrients are removed with the coal, they have to be added subsequently to enable an efficient microbiological process.

Based on the experimental results two process routes can be proposed for the treatment of leaching solutions with a potential utilisation of iron (Figure 18):

Figure 18 - Suggested process routes for the treatment of leaching solutions and possible

iron recovery

The most important aspects for further utilisation of iron precipitates is the concentration of recovered iron in the raw material as well as the content of impurities, which specify the possibilities for further processing and finally the quality of products. High quality of products enables higher revenues, which are necessary for an economical application. As the expected quantities of iron residues are not sufficient due to the low concentrations in the sandstone ore, an economic recovery of iron does not seem to be feasible in the present case from the ore used in the

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BIOMOre project. However, if the in situ leaching technology developed in the BIOMOre project is used in a rock with higher Fe-concentrations resulting in Fe-rich PLS, further utilisation of the precipitates could be promising.

Basic engineering of the process as well as the assessment of capital and operation costs for upscaling to industrial scale were planned with the results of the laboratory testwork with leaching solutions obtained from the Rudna mine. Due to the long duration of the certification procedure for the installation and commissioning of the pilot plant on site and the introduction of an additional water washing phase, there was no real leaching solution from the pilot plant available until the end of the project. For this reason the laboratory testwork was carried out only with leaching solutions prepared by IMN with sandstone ore obtained from Rudna mine. In doing so, an assessment of possible treatment routes was possible but a basic engineering requires reliable data of the real test site. In addition, the sandstone ore was very low in iron, so that there was no excess iron in the process as originally expected. A recovery of Fe for a further utilisation is therefore not economically feasible in the present case, though the processes are relevant and applicable to the treatment of bleed streams to recover iron. Since there is neither a reliable database for the treatment of original leaching solutions from the site nor any excess iron in the streams, basic engineering and an assessment of capital and operating costs were dispensed with.

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3. Technologies and techniques for water balance improvements, industrial removal of iron

3.1. Objectives

Main objectives are included in task 4.5 as follow:

- Do research on techniques and technologies to improve and industrial scale working process for removing or recovering iron. The technology developed needs to be scalable to an industrial plant with sufficient throughput or capacity to be cost-effective in BIOMOre processes or in any other where it could be needed.

- Develop techniques for water balance improvements and water quality improvements allowing the processes to equilibrate to the maximum and to reduce water intake to minimum levels.

- Improvements in water balance issues related to improvements in effluent treatment requirements through membrane based treatment.

- Study methods to attempt zero discharge process environments by recycling the maximum flow of process water and avoiding any discharge to public waterways.

- Interpret results and create design criteria to optimize water balance in any relevant industrial plant. Use information from results interpretation and design criteria from this deliverable to develop a capital and operating cost for upscaling to pilot scale.

3.2. Methodology

3.2.1. Iron removal/recycling

3.2.1.1. State-of-the-art technologies for iron removal/recycling

Literature search has been focused on industrial technologies used to remove iron from solutions and further recovery and recycling to leaching process when necessary.

In addition to iron, other typical detrimental components have been reviewed as well. Relevant outcomes are presented below.

Iron as the 4th most abundant element in the earth’s crust is a common element in ores processed by the metallurgical industry. Dissolution of various sulfide, silicate, oxide and carbonate minerals during processing can release significant quantities of iron to process solutions. Common iron minerals and compounds in hydro-

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metallurgical processing include iron (III) oxyhydroxides (ferrihydrite, goethite, akageneite, lepidocrocite), hematite and jarosite.

Although iron is a simple and common metal its solution chemistry is both colourful and complex. It exhibits 3 oxidation states and forms a variety of strong colourful complexes that provide unique properties and impact on its hydrometallurgical properties.

Relevant Iron Properties:

Similar to cobalt and nickel (sub-group VIII Periodic Table)

Oxidation state usually +2 or +3, but also can be +6 (FeO4)2-

Forms variety of complexes:

Table 12 Examples of Ferric and Ferrous Iron Complexes

Complex Fe2+ Fe3+

Strong CN- CN-,SCN-, OH-, F-

Moderate (COO)22- (SO4)2-

Weak OH-, [SO4]2-, Cl-, NH3 Cl

The role of ferric iron as an oxidant during the acidic leaching of metal sulfides has been known for decades. The chemical reaction can be written for the sulfate system as:

ZnS + Fe2(SO4)3 → ZnSO4 + 2FeSO4 + Sº

CuS + Fe2(SO4)3 → CuSO4 + 2FeSO4 + Sº

Cu2S + 2Fe2(SO4)3 → 2CuSO4 + 4FeSO4 + Sº

Most of the information gathered considers the problematic issues concerning iron (and other components) removal and different technical solutions applied around the world. Some of these pieces of information are in the form of books and papers. More than 50 research papers and books have already been reviewed.

To get a clear picture of the different technologies some specific papers have been found to be especially interesting. Some of these publications offer a general perspective about this technology and provide a comparison between different

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solutions. Most of the information consulted has been published recently, in some cases in 2015.

Precipitation techniques for iron control

To remove iron, the most used process is based on simultaneous combination of iron oxidation and precipitation with lime addition. After that, iron precipitates are removed through filtration techniques, and most of the impurities remain absorbed onto the iron cake. If oxygen transfer is not enough through air sparging, a pre-oxidation treatment with chemical products is used.

In aerated water, the redox potential of the water is such as it allows an oxidation of the ferrous iron into ferric iron which precipitates then as iron hydroxide, Fe (OH)3, thus allowing a natural removal of dissolved iron.

The form of iron in water depends on the water pH and redox potential, as shown in the Pourbaix diagram of iron in Figure 19. Usually groundwater has a low oxygen content, thus a low redox potential and low pH (5.5- 6.5).

Figure 19 - Iron Pourbaix Diagram.

However ground waters are naturally anaerobic, so, iron remains in solution and therefore it is important to remove it for a water use.

The elimination of the ferrous iron, by physical-chemical way, is obtained by raising the water redox potential by oxidation thanks to oxygen of the air and this by simple ventilation. In the case of acid water, the treatment could be supplemented by a correction of the pH. Thus, the ferrous iron is oxidised into ferric iron, which

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precipitates as iron hydroxide, Fe(OH)3. The precipitate is then separated from water by filtration on sand or decantation.

The most frequently used and the cheapest method of iron(III) removal from acidic solutions is precipitation of sparingly-soluble iron hydroxide - Fe(OH)3, goethite - FeO(OH), hematite - Fe2O3 or jarosite - MFe3(SO4)2(OH)6, where M = H, Na, K, NH4, 1/2Pb, precipitated from sulfate solutions. In each case, partial neutralisation is necessary, for example with milk of lime, in order to obtain optimal pH value:

2Fe3+ + 3 Ca(OH)2 → 2Fe(OH)3 + 3Ca2+

2Fe3+ + 3 Ca (OH)2 → 2FeO(OH) + 3Ca2+ + 2H2O.

There are several processes used for iron control, mainly associated to hydrometallurgical zinc production:

1. Jarosite process: this process is the most used in the iron control process, see Figure 20. Before its introduction, poor yields were common in zinc plants because zinc ferrite was discarded with the neutral leaching residue. The jarosite process increased zinc yields from 85% to 98%. The process takes its name from the iron compound that precipitates, of general composition M [Fe3 (SO4)2 (OH)6], where M is any of the Na+, NH4+, H3O+, K+ and ½Pb2+ ions.

The jarosite process begins after leaching with hot acid, as shown in Figure 22. Calcium is added to pre-neutralize the hot acid leach liquor at pH of 1 to 15. To increase total zinc recovery, the thickened residue is returned to the leaching circuit with hot acid to dissolve the zinc ferrite and recover the metal values (e.g., Pb, Ag, Cd, Cu). Alkali metal or ammonium ions are added to the liquor to precipitate iron as jarosite. Because the precipitation of jarosite generates acid, the calcine is added to control the pH between 1.5 and 1.8, generating a filterable product:

Figure 20 - Iron Removal in the jarosite process.

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3 Fe2 (SO4)3 (aq) + M2SO4(s) + 12H2O → 2MFe3(SO4)2(OH)6(s) ↓ + 6H2SO4 (aq)

The overall recovery of zinc with the jarosite process may exceed 98% of the zinc in the concentrate, depending on the iron content. The higher the iron content of the calcine, the lower the yield of zinc. The zinc losses are the result of the zinc ferrite present in the calcine added to the jarosite precipitation stage. Typically, the zinc content in the jarosite precipitates is approximately 4 to 6%, while the iron content is in the range of 25 to 30%. Jarosite is less inert to environmental degradation than goethite or hematite, due to the slow conversion of the basic metal sulfate compound to oxides and hydroxides, releasing acid that can contaminate effluents from tailings ponds.

Goethite process: this iron elimination process causes the iron to precipitate as goethite, FeO (OH), see Figure 21. The goethite is rich in iron (40-45%) and considerably reduces the candidness of a residue.

The goethite process begins at the same point as the jarosite in the zinc circuit, for example, hot acid leaching followed by solid-liquid separation.

Figure 21 - Iron removal in the goethite process.

Precipitation to goethite can be favoured by the precipitation of iron at 100 ºC and at pH with values between 1.5 and 3, if the concentration of Fe3+ in the solution does not exceed 1 g/L. The zinc concentrate is added to the liquor to reduce Fe3+ to Fe2+, at the same time, using the oxidizing capacity of ferric iron to treat more concentrate:

Fe2(SO4)3 (aq) + ZnS (s) → 2FeSO4 (aq) + ZnSO4 (aq) + S(s) ↓

Iron precipitation occurs under oxidizing conditions in the range of pH 2.8-3.0, and pH control is achieved by additions of calcine.

2Fe2 (SO4)3 (aq) + 2ZnO + 1/2O2 → 2ZnSO4 (aq) + 2FeO(OH)(s) ↓

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In an alternative method, the hot acid leaching solution is fed at a rate proportional to the rate of goethite precipitation to stay below a concentration of 1 g/L Fe3+. The acidity generated is neutralized by addition of lime, thus controlling the pH in the range of 2.8-3.0.

Fe2(SO4)3 (aq) + 4H2O → 2FeO(OH)(s) ↓ + 3H2SO4 (aq)

Figure 22 - Effect of the redox potential on the transformation of goethite to hematite.

3. Hematite process: this process aims to produce the marketable product of iron that can be used for cement production, or less likely, in steelmaking, see Figure 23. This process provides an environmental advantage over the processes of jarosite and goethite, replacing a normally disposable product with a potential raw material, but has a more complex flow diagram and implies a higher cost of capital.

This process differs from the two previous processes of iron precipitation because hot leaching occurs, simultaneously with the reduction of Fe3+, by the addition of sulfur dioxide gas at high pressure.

ZnFe2O4 (s) + 2H2SO4 (aq) + SO2 (g) → ZnSO4 (aq) + 2FeSO4 (aq) + 2H2O

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Figure 23 - Iron removal in the hematite process.

The reductive leaching is carried out in an autoclave at a lower temperature than the sulfur melting point, which is added for copper precipitation. After separation of the residue, calcium carbonate is added to neutralise the acidity and precipitate gypsum which, if sufficiently pure, can be used to make cement or used in the construction industry. The purified solution is then heated to 200°C under pressure 10-15 bar in an autoclave where Fe2+ is oxidised to give a precipitate of saleable hematite.

2FeSO4(aq) + 1/2O2 + 2H2O → Fe2O3(s) ↓ + 2H2SO4(aq)

Ion exchange techniques for iron control

It is commonly used for circuit purification, and there are no industrial applications in main stream circuits.

In order to increase the current efficiency in copper electrowinning tank houses, iron can be removed from the electrolyte using ion exchange. While this is a proven technology, very little data is available for the application of this technology to copper electrowinning electrolytes containing antimony and bismuth.

The iron IX system being considered removes ferric iron from electrolyte streams. There are three steps to iron IX: loading, generation of cuprous, and stripping. The chemistry for these three steps is summarized in next equations:

Chemistry: loading

Fe2 (SO4)3 + 6(H-R) → 3H2SO4 + 2(Fe-R3)

Chemistry: Cu Shot Tower

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Fe2 (SO4)3 + Cu → 2FeSO4 + CuSO4

Cu + CuSO4 → Cu2SO4

Chemistry: Stripping

2(Fe-R3) + Cu2SO4 + 3H2SO4 → 6(H-R) + 2FeSO4 + 2CuSO4

Solvent extraction for iron control

There are no industrial applications using solvent extraction for iron control in main hydrometallurgical processing routes. Some extractants have high affinity for iron but they are more focussed to extract high value metals as copper, zinc, nickel, etc.

Fe(III) is extracted at low pH with RCOOH (Versatic acid). Also, a strong iron organic complex is formed with D2EHPA, PC 88A and Cyanex 272. The main problem in the case of D2EHPA is the stripping stage, in this case it is not possible to collect the iron from the organic phase using sulfuric acid solution. The only way is to use reductive acid stripping or a stronger acid such as hydrochloric acid as stripping agent.

Iron precipitation: Laboratory scale testwork.

When the waters of mining and metals industry are acidic, the acidity can be neutralised by the addition of alkaline agents. The most commonly used alkaline agents are: quicklime, hydrated lime, limestone, limestone powder, sodium hydroxide (caustic soda), ammonium hydroxide, etc. The selection of any of these chemicals will be conditioned by its alkalinity performance and cost.

Several studies have been performed about reactions between ferrous iron and oxygen. All of them have been focused to understand the many roles iron may play in mine waters. Special attention should be given to the kinetics of this reaction: the rate at which it proceeds depends on several parameters including pH, temperature, concentration of dissolved oxygen, and catalysts.

Some tests were done in the laboratory to probe the evolution of iron at different pH with combination of iron oxidation and precipitation with lime addition. Studies on iron oxidation in bicarbonate solutions are complicated by the slight solubility of ferrous and ferric iron in such solutions. Ferrous constituents generally are more soluble than ferric constituents.

When limestone or limestone powder is used, it should be noted that it can only raise the pH to 5.5, because the limestone releases carbon dioxide (CO2), which when combined with water forms carbonic acid. For this reason, it is only used as a first neutralisation step. If a higher pH is required, another alkaline agent is required, with or without prior separation of sludge.

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The reaction of Fe (II) with oxygen generally leads directly to ferric hydroxides. The stoichiometric relationship being:

Fe2+ + ¼ O2 + 2OH- + ½ H2O = Fe (OH)3 (s)

The oxidation may occur under certain conditions – especially in buffer solutions with pH values greater than 6 – in a stepwise fashion over the mixed iron (II) – (III) hydroxides and magnetite. The ferrous iron in these intermediates is only very slowly oxidised.

Several representative reaction runs at a constant partial pressure of oxygen and various pH values are plotted in Figure 5. The rate of oxidation was first order with respect to Fe (II) and independent of the Fe (III) concentration. This is evident from the time dependence of any one reaction.

Laboratory tests were done simulating reactors at atmospheric pressure with oxidation and lime addition. Testing was performed with different iron concentration using a synthetic raffinate, see Table 2.

The laboratory test methodology was performed by increasing the pH with lime and air sparger oxidation at the same time. This method can remove iron contained in waste water producing a final concentration of iron below 0.05 mg/l.

At the beginning of the neutralisation, the raffinate with a specific concentration of iron was mixed with lime. At the end, after neutralizing and iron precipitating the solution reach a pH in the range of 8 – 8.5.

Figure 24 - Iron Pourbaix Diagram

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In the final step of the test, the iron concentration in solution obtained determines that the neutralisation and oxidation process is quite efficient, no matter the iron concentration that was feed to the process, see Table 13.

Table 13 Initial and final iron concentration in solution of each test

Test [FeT]o (mg/L) [FeT]f (mg/L)

1 7.93 0.02

2 4.54 0.03

3 3.76 0.01

Using conditions for test number one, a new test was done without oxidation and the result is shown in the next Table 14.

Table 14 Final iron concentration in solution without aeration

Test [FeT]f (mg/L)

1 0.4

3.2.1.2. Conclusions

Process performance of iron precipitation using abovementioned conditions is really high producing liquors with very low levels of iron in solution (less than 30 micrograms per litre)

The aeration of the reactor during the precipitation process is essential to achieve complete iron removal from the solution.

3.2.2. Membrane cell lab scale plant

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The SEPA CF Cell is a laboratory-scale cross flow filtration unit that is designed to evaluate the performance of flat sheet membranes in a variety of applications. It simulates the flow dynamics of larger, commercially available membrane elements such as industrial spiral wound membrane elements.

By using a combination of stainless steel (SS) shims, feed spacers, and membranes, the user can vary the operating conditions and fluid dynamics over broad ranges. A complete lab cell prototype including tanks and all necessary instrumentation was designed, purchased and assembled to be ready for future lab scale testing. The specifications are given in Table 15.

Table 15 Operational parameters and technical specifications of the SEPA CF Cell.

Parameter Description

Membrane active area 140 cm2 (22-inch2)

Hold-up volume 70 mL (2.4 ounces)

Maximum pressure: 316SS cell body 69 bar (1000 psig)

Maximum temperature: 316ss cell body 177 ºC (350 ºF)

O-rings Viton* (Other materials available)

pH range Membrane dependent

Cross flow velocity Variable

Dimensions Description

Slot depth 1.09 mm (0.075 inches)

Slot width 146 mm (5.750 inches)

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3.2.2.1. SEPA CF Cell Components

The complete SEPA CF Cell includes:

Figure 25 - Cell body (top and bottom).

Figure 26 - Anodized aluminium cell holder with piston and high pressure gauge.

Figure 27 - Anodized aluminium cell holder with piston and high pressure gauge.

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3.2.2.2. SEPA CF Cell Assembly

a) Cell body assembly:

Figure 28 - Typical cell body assembly

Also, additional components are necessary to operate the SEPA CF cell. In the next list all the necessary components can be seen, see Table 16.

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Table 16 Components necessary to operate the SEPA CF Cell.

Item Description

1 Concentrate/feed tanks (12 litres)

2 Two feed pumps (3 HP, 50 Hz, 230 V, 69 bar, 120 psi)

3 Sepa CF Cell

4 Concentrate control valve

5 Permeate collector

6 Needle valve with „T“ for bypass, 3/8“ Tube Connection

7 Pressure gauge with „T“, 3/8“ Tube Connection

8 Flow meter

9 Pulsation dampener

10 Feed tank crossflow

11 Cooling

Pipe Description

A 3/8“ Nylon tube fittings

B 3/8“ High pressure stainless braided hose

The flow diagram that has been designed to assemble the membranes at laboratory scale, is shown in the following Figure 28:

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Figure 29 - Membrane lab scale flowsheet.

3

5

A

PIPI

B

2 2

9 9

1

A7

4

A

Outlet

Outlet

FM

10

B

Inlet Inlet

B

FM

B

B

B

4

7 8

8

66

11

11

Outlet

Item Description1 Feed Tank FORWARD (5 litros)2 Feed Pump (3 HP, 50 Hz, 230 V, 69 bar, 120 psi)3 Sepa CF Cell4 Concentrate Control Valve5 Permeate Collector6 Needle valve with "T" for bypass, 3/8" Tube Connection7 Pressure gauge with "T", 3/8" Tube Connection8 Flow Meter9 Pulsation Dampener10 Feed Tank CROSSFLOW11 Cooling

Pipe DescriptionA 3/8" Nylon Tube FittingsB 3/8" High Pressure Stainless Braided Hose

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The final assembly, with all the necessary equipment is shown in Figure 29 and 30.

Figure 30 - SEPA lab scale plant.

Once of the SEPA CF Cell has been assembled and connected to a feed system, it can be used in variety of applications that includes reverse osmosis and nanofiltration.

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Figure 31 - SEPA cell components, stainless steel cell body, top and bottom.

3.2.2.3. Basic Principles of Membrane Filtration

Membrane technology is a physical process for the separation of solution mixtures in which a thin layer of material a few microns thick functions like a filter. The separated substances are not thermally, chemically or biologically modified. New concepts have emerged in recent years – such as membrane contactors or functionalisation – that extend considerably the fields of applications and the interest for membrane technology.

A membrane material is a permeable or semi-permeable thin layer barrier between two phases that restricts the motion of certain components.

Membranes can transport one component from the upstream side phase to the downstream side more readily than any other component or components, and as such induces separation. Porous thin layers are also getting considered as very efficient tools to contact different phases.

Membrane processes are many. They vary in molecular separation size and in the driving force expended:

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Figure 32 – Different filtering mechanisms.

- Microfiltration: Microfiltration (MF) closely resembles conventional coarse filtration and deals with the separation of particles between 0.1 and 10µm, such as suspended solids (colloids), bacteria and large proteins. MF is applied for clarification and sterilisation purposes, for cell harvesting, separation of oil-water emulsions, etc.

- Ultrafiltration: Ultrafiltration (UF) belongs to the pressure-driven membrane processes. This technique uses microporous membranes with 1-100 nm pore diameters. Such membranes let through small molecules (water, salts) and adopt the high molecular weight molecules (polymers, proteins, colloids). Operating pressures are typically in the range of 1 to 5 bars for cross-flow application. UF is ideally suited for fractionation, concentration and purification purposes.

- Nanofiltration: Nanofiltration (NF) is a pressure-driven membrane process which is preferentially used for the recycling of aqueous solutions. Operating pressures are between 5 and 20 bar.

- Reverse Osmosis: Reverse Osmosis (RO) is used to separate components of a solution. It is based on a pressure-driven process, the driving force resulting from the difference of the electrochemical potential on both sides of the membrane. Operating pressures can range from 10 bars up to 100 bar. A typical RO application is seawater desalination.

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3.2.2.4. Basic Principles of Crossflow Filtration

In crossflow filtration systems, feed streams flow tangentially over the surface of a membrane filter. Some of the feed stream will permeate through the membrane while the rest will continue to flow through the system as a concentrate. The tangential flow across the membrane reduces the fouling rate by increasing the back transport of fouling agents from the membrane surface, through inertial lift, surface drag, and shear diffusion mechanisms. The feed’s tangential/cross flow also reduces the concentration polarisation formed at the membrane surface, further reducing the membrane’s fouling rate.

Sterlitech’s bench-scale crossflow filtration systems provides users with a modular system compatible with a wide range of applications across an array of disciplines. It is designed to be versatile enough to meet the dynamic needs of researchers and engineers alike and is ideal for research and development, small batch processing, and simulating larger commercial processes.

Cross flow velocity is calculated by dividing the volumetric flow rate through the cell by the cross-section area of the cell.

3.2.2.5. Examples of different crossflow studies

The following studies utilised the Sterlitech crossflow cells in their method and are listed here to illustrate the potential applications for crossflow filtration. These studies are good references for understanding the operation of the Sterlitech’s crossflow cells.

1. Reverse Osmosis (Desalination): Sachit, Dawood Eisa. “Analysis of reverse osmosis membrane performance during desalination of simulated brackish surface waters.” Journal of Membrane Science. 453. (2014): 136-154.

2. Forward Osmosis and Low Pressure Reverse Osmosis: Yangali-Quintanilla, Victor, Zhenyu Li, et al. “Indirect desalination of Red Sea water with forward osmosis and low pressure reverse osmosis for water reuse.”Desalination. 280. (2011): 160-166.

3. Ultrafiltration (Food Processing): Post, Antonie, Hanna Sampels, et al. “A comparison of micellar casein and β-casein as sources of basic peptides through tryptic hydrolysis and their enrichment using two-stage ultrafiltration.”International Journal of Dairy Technology. 65.4 (2012): 482-489.

4. Ultrafiltration and Nanofiltration (Protein Production): Ranamukhaarachi, Sahan, Lena Meissner, et al. “Production of antioxidant soy protein hydrolysates by sequential ultrafiltration and nanofiltration.” Journal of Membrane Science. 429. (2013): 81-87.

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3.2.3. Membrane Development

3.2.3.1. Types of membranes used The membranes that have been chosen to perform the tests are those shown below in the following Table 17:

Table 17 Different types of membranes used in the filtration tests.

The applications for which the membranes that have been chosen are most frequently used are shown in the next Table 18 below.

Table 18 Most commonly used applications of several membranes

Manufacturer Type MWCO (Dalton)

Polymer Feed pH Flux

(GFD/ psi)

Rejection

Dow Filmtec™ NF90~200-400

Polyamide Industrial/

Commercial Water

02-11 46-

60/130 99.0%

MgSO4

GE Osmonics™

Duracid

~150-200

Thin Film Surface/

Groundwater0-9

10-19/225

98.0% MgSO4

DL ~150-300

Thin Film Foods/Indust

rial Water02-10 28/220

98.0% MgSO4

TriSep™

TS80 ~150 Polyamide Foods/Indust

rial/ Wastewater

02-11 20/110 99.0%

MgSO4 (80-90% NaCl)

XN45 ~500 Polypiperazi-

neamide

Foods/Industrial/

Wastewater02-11 35/110

95.0% MgSO4 (10-30% NaCl)

Designation Application

NF90 Seawater sulfate removal, landfill leachate treatment.

Duracid

DL Heavy metal removal

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3.3. Results

3.3.1. Preliminary Membrane Tests: Magnesium Sulfate solution

The prototype was started up using magnesium sulfate solution to determine system efficiency using GE Osmonics DL and TriSep XN45 membranes. The conditions under which the tests were performed are shown in the following Table 19 and the tests parameters in the Table 20.

Table 19 Test conditions.

Table 20 Test parameters

Rejection percentages indicated by manufacturers are reached.

TS80 Softening NF

XN45 Process NF

Test Conditions

Temperature

Hydraulic

pressure

Test Time

Membrane Feed

Concentration

Feed Volume

Cell Pressur

e

Feed Flow

25ºC 40Bar 20min GE Osmonics

DL & Tripset XN45

2000ppm MgSO4

10 L 10 Bar 100 L/h

Preliminary Tests

Pressure (Bar)

Test Time (min)

Feed Flow (L/h)

Permeate Flow (L/h)

Permeate Volume (mL)

SO4 Rejection

(%)

Mg2+ Rejection

(%)4.8 3 100 0.58 30 92.9 98.4

10 6 100 0.92 65 96.4 98.4

10 9 100 0.92 95 92.9 97.8

10 12 100 0.92 125 92.9 97.8

10 15 100 0.92 150 89.3 97.8

10 18 100 0.92 180 89.3 97.8

10 >20 100 0.92 210 92.9 97.8

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Figure 33 Percentage of transmission in SO4= and Mg2+.

Figure 34 Percentage of rejection in SO4= and Mg2+

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3.3.2. Tests with Secondary Copper Raffinate

A simulated stream using current secondary copper raffinate from the CLC plant was used for a testing campaign using GE Osmonics DL and TriSep XN45 membranes. The DOE conditions used are shown in the next Table 21 shown below:

Table 21 DOE Conditions.

Design of Experiments

An experiment design to determine the main process parameters in membrane rejection was performed. The ultrafiltration membranes, GE Osmonics DL and TriSep XN45 were selected as the most promising for this application. The objective was to obtain the behaviour of the different membranes in terms of impurities removal from water.

Design Information: The full factorial design chosen is 22 type.

Table 22 Factorial design 22.

DOE Conditions

Temperature

Hydraulic pressure

Test Time

Membrane Feed

Concentration

Feed Volume

Cell Pressur

e

Feed Flow

25ºC 40Bar 30min GE Osmonics

DL & Tripset XN45

Secondary Raffinate

10 L Variable Variable

Factorial Design 2^2

Variables Low (-) High (+) Medium (0)

Pressure (Bar) 10 30 20

Feed Flow (L/h) 120 180 150

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Design matrix:

Table 23 Design matrix

• Results

The results are shown below in the next page.

MATRIX

Test Pressure Flow

1 - -

2 + -

3 - +

4 + +

5 - +

6 - -

7 0 0

8 0 0

9 + -

10 + +

11 0 0

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Table 24 Parameters results with GE Osmonics DL membrane

Table 25 Parameter results with TriPSet XN45 membrane.

TEST Pressure

(Bar)

Feed Flux

(L/min)

Permeate Flux (L/h)

Tª (ºC) %Rej Cu %Rej Fe %Rej Ca %Rej Co %Rej Mn %Rej Zn %Rej Al %Rej Mg

1 10 2 0.36 22.1 99.83 98.29 99.89 99.92 99.92 99.86 99.94 99.92 2 30 2 0.78 24 99.59 98.74 99.78 99.80 99.83 99.66 99.94 99.841 3 10 3 0.42 25.6 99.84 98.81 99.89 99.91 99.92 99.85 99.92 99.92 4 30 3 1.2 29.6 99.57 99.29 99.76 99.79 99.81 99.62 99.89 99.69 5 10 3 0.5 29.9 99.81 98.87 99.88 99.91 99.91 99.82 99.98 99.90 6 10 2 0.4 29.3 99.83 98.53 99.89 99.91 99.91 99.81 99.92 99.92 7 20 2.5 0.81 31.4 99.65 99.03 99.81 99.83 99.84 99.65 99.92 99.79 8 20 2.5 0.77 33.2 99.69 98.95 99.82 99.81 99.85 99.68 99.86 99.82 9 30 2 0.96 34.5 99.56 98.42 99.76 99.80 99.79 99.59 99.83 99.81

10 30 3 1.07 36.3 99.62 99.17 99.79 99.85 99.78 99.61 99.88 99.74 11 20 2.5 0.86 35.9 99.70 99.02 99.84 99.82 99.82 99.68 99.91 99.74

Nº de experimento

Presión (Bar)

Q Feed (L/min)

Q Perm (L/h)

Tª Feed(ºC) %Rej Cu %Rej Fe %Rej Ca %Rej Co %Rej Mn %Rej Zn %Rej Mg

1 10 2 0.42 24.9 99.64 97.35 99.76 99.83 99.83 99.73 99.86 2 30 2 1.08 25.5 99.5 98.87 99.64 99.78 99.82 99.57 99.75 3 30 3 1.26 27.2 99.28 99.15 99.7 99.81 99.86 99.62 - 4 20 2.5 0.85 27.3 99.68 99.16 99.79 99.88 99.91 99.72 - 5 30 2 1.14 28.6 99.5 99.18 99.70 99.80 99.86 99.59 - 6 10 3 0.45 29 99.76 99.03 99.86 99.92 99.93 99.81 99.88 7 20 2.5 0.94 29.9 99.55 99.20 99.73 99.82 99.88 99.64 - 8 10 3 0.48 30.2 99.76 99.02 99.86 99.89 99.93 99.79 99.9 9 10 2 0.45 29.9 99.75 98.91 99.85 99.89 99.92 99.78 99.91

10 20 2.5 0.91 31.3 99.52 99.19 99.72 99.81 99.86 99.60 - 11 30 3 1.36 31 99.55 99.33 99.74 99.89 99.89 99.62 -

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a) Contour Plots for membrane GE OSMONICS DL: 1. Calcium:

Figure 35 - Calcium Contour Plot. GE OSMONIC DL.

Figure 36 - Calcium Linear Model. GE OSMONIC DL.

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Figure 37 – Calcium Pareto Diagram. GE OSMONICS DL.

2. Copper:

Figure 38 - Copper Contour Plot. GE OSMONIC DL.

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Figure 39 - Copper Linear Model. GE OSMONICS DL.

Figure 40 - Copper Pareto Diagram. GE OSMONICS DL.

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3. Iron:

Figure 41 - Iron Contour Plot. GE OSMONIC DL.

Figure 42 - Iron Linear Model. GE OSMONICS DL.

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Figure 43 - Iron Pareto Diagram. GE OSMONICS DL.

4. Manganese:

Figure 44 - Manganese Contour Plot. GE OSMONIC DL.

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Figure 45 - Manganese Linear Model. GE OSMONICS DL.

Figure 46 - Manganese Pareto Diagram. GE OSMONICS DL.

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5. Zinc:

Figure 47 - Zinc Contour Plot. GE OSMONICS DL.

Figure 48 - Zinc Linear Model. GE OSMONICS DL.

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Figure 49 - Zinc Pareto Diagram. GE OSMONONICS DL.

b) Contour Plots for membranes TriPSet XN45:

1. Calcium

Figure 50 - Calcium Contour Plot. TIPSET XN45.

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Figure 51 - Calcium Linear Model. TRIPSET XN45.

Figure 52 - Calcium Pareto Diagram. TRIPSET XN45.

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2. Copper:

Figure 53 - Copper Contour Plot. TRIPSET XN45.

Figure 54 - Copper Linear Model. TRIPSET XN45.

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Figure 55 - Copper Pareto Diagram. TRIPSET XN45.

3. Iron:

Figure 56 - Iron Contour Plot. TRIPSET XN45.

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Figure 57 - Iron Linear Model. TRIPSET XN45.

Figure 58 - Iron Pareto Diagram. TRIPSET XN45.

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4. Manganese:

Figure 59 - Manganese Contour Plot. TRIPSET XN45.

Figure 60 - Manganese Linear Model. TRIPSET XN45.

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Figure 61 - Manganese Pareto Diagram. TRIPSET XN45.

5. Zinc:

Figure 62 - Zinc Contour Plot. TRIPSET XN45.

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Figure 63 - Zinc Linear Model. TRIPSET XN45.

Figure 64 - Zinc Pareto Diagram. TRIPSET XN45.

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3.3.3. Concentration Test

In addition to the previous testing a dedicated concentration test was performed using the Tripset XN45 membrane. The previous DOEs were performed to determine the performance of the process depending on operating conditions. As a result, tests were carried out under conditions similar to the best ones. Testing conditions are summarised in next Table 15.

Table 26 Testing conditions for Tripset XN45 membrane.

Conditions

Temperature (ºC)

Pressure (Bar)

Test Time(H)

Membrane type

Feed Initial Feed Volume (L)

Final Permeate Volume (L)

25 30 4.5 Tripset XN45

2º Raffinate diluted 50%

10 4.3

The following results were obtained.

Table 27 Testing conditions for Tripset XN45 membrane.

Feed

(mg/L) Retentate

(mg/L) Permeate

(mg/L) %Concentration % Rejection

Cu 341 527 27.7 35.29 91.88

Fe 7700 12950 327 40.54 95.75

Ca 355 602 22 41.03 93.80

Zn 577 931 35 38.02 93.93

Na 591 787 332 24.91 43.82

SO4 37200 52200 17050 28.74 54.17

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Table 28 Parameters results with Tripset XN45 membrane.

BM_XN45_ALTA PRESIÓN

Muestra Cu Fe Ca Zn Na SO4

g/L g/L g/L mg/L mg/L mg/L

BM_C1_XN45_PER1H 0,0246 0,209 0,022 31 309 16950

BM_C1_XN45_PER2H 0,0274 0,23 0,018 29 320 17250

BM_C1_XN45_PER3H 0,0214 0,254 0,014 22 301 15700

BM_C1_XN45_PER4H 0,0266 0,294 0,022 33 322 16550

BM_C1_XN45_PER4,5H 0,0277 0,327 0,022 35 332 17050

BM_C1_XN45_FEED 0,341 7,7 0,355 577 591 37200

BM_C1_XN45_RET1H 0,383 8,94 0,412 660 649 41300

BM_C1_XN45_RET2H 0,471 10,1 0,462 691 693 44600

BM_C1_XN45_RET3H 0,477 10,95 0,509 787 712 45900

BM_C1_XN45_RET4H 0,501 12 0,537 864 752 49100

BM_C1_XN45_RET4,5H 0,527 12,95 0,602 931 787 52200

Table 29 Parameters results with Tripset XN45 membrane.

BM_XN45_ALTA PRESIÓN

Muestra Flow Feed (L / min)

Flow Perm (mL / min)

Caudal Perm (L/h)

Tª Feed (ºC)

Vol Feed % Recovery % Rejection

Fe % Rejection

Ca % Rejection

Zn % Rejection Na

% Rejection SO4

BM_C1_XN45_1H 3 17,54 1,05 28,2 9,98 99,275 97,346 99,759 99,728 99,042 99,217

BM_C1_XN45_2H 3 16,67 1,00 30,2 9,96 99,275 99,148 99,696 99,618 96,757 97,738

BM_C1_XN45_3H 3 15,31 0,92 31,3 9,94 99,496 99,182 99,703 99,594 96,845 97,909

BM_C1_XN45_4H 3 13,95 0,84 32,4 9,92 99,549 99,204 99,734 99,643 97,087 98,088

BM_C1_XN45_4,5H 3 13,04 0,78 32,7 9,9 99,751 99,910 99,849 99,784 98,424 99,124

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3.3.4. Tertiary Test: PLS stream from CLC

A PLS stream from the CLC plant was used to produce a solution very similar to BIOMOre expected PLS. The aim was to simulate the BIOMOre PLS behaviour using TripSet TS80, GE OSMONICS DURACID and Dow Filmtec NF90 membranes. The objective is to conduct concentration tests to assess the technology for the BIOMOre project.

The most relevant data are included below:

a) TripSet TS80 membrane:

Table 30 Conditions operation with Tripset S80 membrane.

Table 31 Obtained results using Tripset S80 membrane.

Conditions Initial

Temperature (ºC)

Feed flow

(L/min)

Pressure (Bar)

Test Time(H)

Membrane Feed

Concentration

Permeate Total

Volume

21 3 20 8 Tripset

TS80 PLS 3340

PLS

(mg/L) Retentate

(mg/L) Permeate

(mg/L) %

Concentration % Rejection

Cu 2390 3390 50,20 29,50 97,90

H+ 22600 28600 6500 20,98 71,24

Fe 8510 11950 146 28,79 98,28

Ca 617 869 14 29,00 97,73

Zn 8290 11850 169,5 30,04 97,76

Na 110 150 3 26,67 97,27

SO4 48500 65000 7100 25,38 85,36

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Table 32 Obtained results using Tripset TS80 membrane.

BM_C3_TS80

Sample Pressure

(Bar) Feed Flow

(L/min) Feed Flow (L/h)

Permeate Flow (mL/min)

Permeate Flow (L/h)

Retentate Flow (L/h)

pH Retentate pH Permeate Tª

Feed/Retentate (ºC)

Tª Permeate (ºC)

1 HOUR 20 3 180 8,57 0,51 179,49 1,00 1,03 24,20 18.70

2 HOURS 20 3 180 7,69 0,46 179,54 0,93 0,94 24,70 18,10

3 HOURS 20 3 180 7,14 0,43 179,57 0,95 1,02 25,20 19,70

4 HOURS 20 3 180 6,67 0,40 179,60 0,83 0,87 25,20 19,20

5 HOURS 20 3 180 6,52 0,39 179,61 0,93 0,98 26,00 20,40

6 HOURS 20 3 180 6,12 0,37 179,63 0,83 0,86 26,10 20,70

7 HOURS 20 3 180 6,00 0,36 179,64 0,92 1,00 27,50 21,30

8 HOURS 20 3 180 5,94 0,36 179,64 0,94 1,03 28,20 22,00

Figure 65 - Permeate Flow vs. Time Evolution.

Figure 66 Retentate Concentration Evolution vs. Time.

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Figure 68 Permeate Concentration Evolution vs. Time.

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b) GE Osmonics Duracid:

Table 33 Testing Parameters for GE O. Duracid membrane.

Table 34 Analytical results of the final solution obtained in the test.

Conditions

Temperatura inicial (ºC)

Pressure (Bar)

Test Time(H)

Membrane Active

Surface (m2)

Feed Flow

(L/min)

Feed Concentration

Permeate Total

Volume

21,6 20 8 GE-

OSMONICS DURACID

0,014 3 PLS_2 2,68

PLS (mg/L)

Retentate (mg/L)

Permeate (mg/L) %Concentration % Rejection

Cu 1695 2350 148 27,87 91,27

Fe 8100 10450 335 22,49 95,86

Ca 114 271 16 57,93 85,96

SO4 35400 44900 7040 21,16 80,11

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D4.5 |


Figure 72 Permeate Concentration Evolution vs. Time

D4.5 |

c) Dow Filmtec NF90:



Conditions

Temperatura inicial (ºC)

Pressure (Bar)

Test Time(H)

Membrane Active

Surface (m2)

Feed Flow

(L/min)

Permeate Total

Volume

16,1 30 11 Dow

Filmtec NF90

0,014 3 6,04

PLS (mg/L) Retentate

(mg/L) Permeate

(mg/L) %Concentratio

n %

Rejection

Cu 1845 3450 25 46,5 98,63

Fe 8230 15400 104 46,6 98,74

Ca 230 428 3 46,3 98,70

SO4 38400 69500 2280 44,7 94,06

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Figure 73 Permeate Specific Flow vs. Time Evolution.


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D4.5 |

3.4. Discussion

During the development of the BIOMOre project, the different technologies for iron removal have been reviewed to define the necessary treatment to be used for the project.

Experimental testing devoted to remove iron using alkali precipitation has showed high efficiency and sufficient information for process design has been gathered.

A prototype for water treatment using membranes technologies has been developed and constructed during the course of the project.

The testing campaign using membrane technology has produced very promising data, high separation factors for water impurities have been obtained with rather good concentration of the retentate. High metals rejection has been obtained using GE Osmonic, Dow Filmtec and TripSet membranes. The final selection of a membrane to be used in the project will be based on availability and prices, as they present similar process behaviours.

D4.5 |

Publication bibliography Bigham, J. M.; Carlson, L.; Murad, E. (1994): Schwertmannite, a new iron oxyhydroxysulphate from Pyhäsalmi, Finland, and other localities. In Mineralogical Magazine 58 (393), pp. 641–648. DOI: 10.1180/minmag.1994.058.393.14.

Bigham, J. M.; Schwertmann, U.; Carlson, L.; Murad, E. (1990): A poorly crystallized oxyhydroxysulfate of iron formed by bacterial oxidation of Fe(II) in acid mine waters. In Geochimica et Cosmochimica Acta 54 (10), pp. 2743–2758. DOI: 10.1016/0016-7037(90)90009-A.

BAFU (2015)- Bundesamt für Umwelt: Verordnung über die Vermeidung und die Entsorgung von Abfällen (VVEA)

Cornell, Rochelle M.; Schwertmann, Udo (2003): The iron oxides. Structure, Properties, Reactions, Occurences and Uses. 2nd, Completely Revised and Extended ed. Weinheim: Wiley-VCH. Available online at http://www.myilibrary.com/?id=56077.

HeGo Biotec (Ed.) (2015): Produktspezifikation FerroSorp DG.

Wilck, Stefan (2011): Veredlung von Eisenhydroxisulfaten aus Tagebauwässern durch Anwendung von Mikrowellenenergie. Dissertation. Technische Universität Berlin, Berlin. Fakultät III, Prozesswissenschaften.

J.E. Dutrizac (1996): B.A.Sc.; M.A.Sc., PhD., F.C.I.C., F.C.I.M. Mining and Mineral Sciences Laboratories. CANMET, Ottawa, Canada

Jukka Tannien, Mika Manttari, Marianne Nystrom (2006): Acid separation with nanofiltration - effect of electrolyte strength and Donnan forces.

Thien Trung Le, Angeli D. Cabaltica and Van Mien Bui (2014): Membrane separations in dairy processing.

Sterlitech Corporation, Sepa CF Cell: Asembly and Operation Manual.

Sterlitech Corporation: Crossflow Filtration Handbook.

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