novedades en lixiviación, extracción por solventes y electro-obtención; intermín; antofagasta;...

Novedades en Lixiviación, Extracción por Solventes y Electro-obtención; Intermín; Antofagasta; Mayo 2005

NOVELTIES IN LEACHING, SOLVENT EXTRACTION AND

ELECTROWINNING

Carlos Avendaño V.


THE GENERAL OBJECTIVES OF TERRAL’S INNOVATIONS ARE:

The Specific Objectives are: Increase process efficiencies:

Obtaining higher recoveries, or quantities of recovered species, or decreasing reagents’ consumption.

Optimize the business approach:Discovering and analyzing the business risk factors.

Reduce investments:By means of plant and equipment configurations that take the best advantage of the knowledge, technology and available resources. Reduce exploitation costs:By decreasing consumptions, or improving rich solutions, or reducing errors.

Environmental improvements:To avoid remediations and generation of environmental liabilities.

Reduce risks and, Try to maximize economical benefits .



THE “TLM METHODOLOGY” (Targeted Leach Method) * The traditional steps to evaluate a heap leaching imply

performing mineralogical and chemical assays and other basic determinations, which are followed by column tests under different leaching conditions, to discover the ones that will bring the best results.

* However, the real experience shows the leaching conditions identified through these procedures are seldom effective when applied in practice.

* Terral’s Approach:- Recognizes the characteristics and the behavior of the ore, - Separates the conditions that must be observed and the available

degrees of freedom, - Conciliates both aspects and establishes an objective based on the economical criteria of an operation


THE “TLM METHODOLOGY” (Targeted Leach Method)* Analyzes the leaching driving forces of the ore, under

contexts different than the traditional ones,* Inserts preliminary “Iso-pH” column tests to establish the

mutual thermodynamic and kinetic interactions between copper metallurgical recoveries, impurity dissolution and acid consumption and their related leaching ratios,

* Defines the context of a complete LX-SX-EW plant, to evaluate the possible interactions between the various sections of a complete plant,

* Enables clients to define their target PLS quality conditions,

* Performs a mathematical modeling of the most optimal way to conciliate process conditions to achieve the clients’ objectives and to leach under optimal conditions, and

* Performs verification tests on the compliance of the objectives.


THE “TLM METHODOLOGY” (Targeted Leach Method)

Fig. Nº 1RECOVERY VS. IRRIGATION RATIO

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0 5 10 15 20 25 30 35 40 45 50 55 60 65

Leaching Time (days)

% Cu

Recovery

(Cab Rec)

Recovery Iso pH Recovery Modeled Col. Recovery Client Refer.

Terral-Estudios


THE “TLM METHODOLOGY” (Targeted Leach Method) Fig. Nº 2

RECOVERY VS. IRRIGATION RATIO

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0 0,5 1 1,5 2 2,5 3 3,5 4Irrigation Ratio (m3 /TM)

% C

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Recovery Iso pH Recovery Modeled Col. Recovery Client ReferenceAcid Cons. Iso pH Acid Cons. Reference Col. Acid Cons. Modeled Col.

Terral-Estudios

Aci

d N

et C

onsu

mpt

ion

kg/T

M

Additional Recovery

Acid Consumption Saving

Solution Pumping Saving

Other advantages:- Cleaner PLS - PLS with higher pH => Higher T.N. in SX- Less Impurities in PLS

Study Columna Iso-pH Estudio

Modeled Column

Column for Industrial Referencel



REFERENCES Is o pH Column Re fe re ntia l Co lumn S imula tion Co lumnTe s t Conditio n Mod. 1,2m: Cur./ PLS/ ref. p/5,5 g/ l

Irriga tion S che dule Puls ing Continuous Pulse 50% and Resting 1d/ 2m

Ite m UnitCu grade Column % Cu tot. 0,97 1,01 1,02Tota l Fe Grade % Fe tot. 5,05 4,80 5,01Column Height m 1,01 1,20 1,20Appa rent Dens ity Kg/l 1,53 1,50 1,50Average Ins tant. Irriga tion Ra te l/h/m2 10,07 7,40 6,13Average Irriga tion Ra te l/h/m2 4,28 7,40 2,88Average Evapora tion l/m2/day 8,62 1,05Tes t Advance Tota l Pe riod days 29,00 34,00 60,00Tota l Irriga tion Ra te m3/TM 2,23 3,83 2,32Cu Recovery (solution) % 80,02 70,86 80,24Idem (re sp. Soluble Cu till CN-) % 82,45 77,52 82,68Tota l Contribution Free Acid Kg/TM 125,66 79,90 50,34Tota l Consum. Free Acid Kg/TM 124,51 77,55 49,26Tota l Acid Cons . (free /comb.) Kg/TM 80,81 60,96 146,26Gangue Acid Consumption Kg/TM 112,53 66,53 36,60Fe Recovery (tota l) % 25,56 -8,21 -6,89Fe Recovery (tota l) Kg/TM 12,91 -3,94 -0,03Al Recove ry (tota l) Kg/TM 6,93 0,37Mg Recovery (tota l) Kg/TM 5,35 1,38

Ite m Ave rag e Ave rage Ave rage[Free Acid] irriga tion gr/lt 45,22 13,04 14,55[Tota l Acid] irriga tion gr/lt 45,22 41,36 73,79[Cu+2] irriga tion gr/lt 0,00 1,01 1,28[Fe t.] irriga tion gr/lt 0,00 13,58 5,32[Fe+3] irriga tion gr/lt 0,00 3,35 2,70Eh irriga tioon mV 551 616 653,07[Free Acid] percol. gr/lt 0,56 0,69 0,49[Tota l Acid] percol. gr/lt 21,99 36,47 18,98[Cu+2]pe rc. Seg./solution gr/lt 3,81 2,96 5,09[Cu+2]pe rc. Seg./solids gr/lt 3,81 1,94 3,74[Fe t.]percola ted gr/lt 6,33 13,78 4,05[Fe+3]percola ted gr/lt 5,07 8,03 4,04De lta [Eh] (percola ted-irriga tion) mV 25 35 208,50De lta [Cu+2] (pe rcola ted-irriga t.) gr/lt 3,81 1,95 3,81



CONFIGURATION OF A BALANCED LX-SX-EW SYSTEM (BY RECIRCULATION OF ACIDULATED PLS)

Curing

Ore Acid (eventual)

PLS

Raffinate

Water

Raff. to PLS

PLS to PLS

Raff. to PLS

Water to PLS

Acid

Water (eventual)

Acid

Electrolyte Bleed

EW Plant Water

Acid

Water

SX Extraction Stages

Unloaded Org.

Org. Tk. Loaded Org.

SX Strip. Stages SX Org.

Wash Stage



Table 2 – Comparison of Objectives and Results

Table 2 – Comparison of Objectives and Results Simulation Analysis w/PLS Target Real Cu Recovery (per solutions) % 80,02 80,24 Total Acid Consumption Kg/MT 43,99 49,26 Gangue Acid Consumption Kg/MT 30,64 36,60 Total Irrigation Ratio gr/lt 2,21 2,32 Total Days Only Irrigation days 36,77 59,00 Irrigation Ratio w/PLS m3/MT 0,44 0,40 PLS Volume Total Drained l 33,17 34,42 [Cu+2]PLS to Irrigation gr/lt 5,65 5,25 [Cu+2]PLS to SX gr/lt 5,65 5,09 [Free Ac.]PLS to Irrigation gr/lt 0,10 0,10 [Free Ac.] PLS to SX gr/lt 0,50 0,49 [Fe tot.] PLS to SX gr/lt 5,00 4,05 pHPLS to SX 2,35 Irrigation Ratio with Raffinate m3/MT 1,76 1,84 Irrigation Days w/Raffinate days 26,43 49,00 [Cu+2]Raffinate to Irrigation gr/lt 0,45 0,45 [Ac. Libre]Raffinate to Irrigation gr/lt 17,83 17,56 [Fe tot.] Raffinate to Irrigation gr/lt 5,00 5,41


THE “BC” APPROACH (Business Configuration)

• This approach is located in the field of the project engineering methodologies.

• Every project is approached on the basis of profitable expectations, and whatever occurs against this objective should be considered as a risk.

• Both the success and risk factors are evaluated during the conceptual stages of the business study, under an economical point of view.


Sets up the general configurations of the heaps and plant processes and develops other detail aspects, and calculates the mass balances.


Designs equipment and facilities for the plant implementation according to the selected alternatives, limited by the precision level of the available data.

Calculates the demands of raw material, energy and services consumption, which are consistent with processes and configurations, to deduct direct costs from the considered alternatives.

Calculates investments in the plant configuration alternatives and infrastructures, using data banks or quotations to conciliate calculations with the precision level of the basis data.

Establishes the organization of each alternative – such as personnel and external services demands - in order to calculate indirect costs.

Calculates the econometric indexes of the project approach alternatives to compare them in the corresponding sceneries.


The “BC Approach” counts on calculation modules that transfer their information through links in order to keep it permanently coordinated, and to reduce revision arising from changes, to save time and costs:


* Configuration and Mass Balance Module.* Heap Leaching Configuration Module.* Pre-Sizing of Equipment and Facilities Module.* Investment Calculation Module.* Cost Calculation Module.* Econometric Indicators Calculation Module.* Design of Equipment Details Module.


Business Organization Stage:The objectives of the first calculation exercise are to show the project implementations to discover the risk factors caused by high investment costs or by other reasons.


* Project calculations are carried out with the available data, considering the desired production, or the estimated ore treatment rate, and metallurgical data or any other project conditioning aspect.

* The configuration alternatives are then parallely modeled, either regarding capacity or any other aspect, mainly related to mass balance and implementations for different process approaches.

* The important issue about the solution of the mass balance module (from the studied alternatives), relies on the fact that the decisions to solve and construct it are based on the project configuration.


THE “BC” APPROACH (Business Configuration)The comments, observations and corrections to the first exercise of the business organization lead us to new and consecutive calculation exercises, in order to:- Explain the project advances to the owner, in order to incorporate

his indications, restrictions, and perceptions on risk factors, and carry out the desired solution assays.

- Consider evaluation factors and start discarding, until the “best option” is selected upon the basis of objective factors.

- Even though the engineering is only an organizational factor in this stage, the project is conceptualized, the predictable risk factors are under control, with the flexibility degrees upon any unexpected events.

- Under the traditional engineering concepts, it will look as if a “conceptual engineering” at a very advanced stage in technical issues – between Basic and Detail Engineering – has taken place.


Design Stage:

The “BC Approach” elements can be perfectly used to formulate the official, traditional engineering documents, such as specification plans, reports and others.

Detail design modules are used in this stage, containing the information on the best alternative selected.



OTHER NOVELTIES IN LEACHING

Practically all the novelties are related to the “TLM Methodology”. In some cases they are part of its grounds and, in others, they are a consequence of such methodology.

Interfering Agents Control.

One of the “TLM” grounds is a more careful recognition of the mineral.

As a result of such recognition, we can find a series of natural species that interfere with the leaching process, such as:


Control of Interfering Agents

* Reductants: Species with the ability to precipitate copper, previously dissolved by the reagents, thus copper remains in the ore as a metallic precipitate, unlikely to re-dissolve, as a consequence of a loss of recovery capacity phenomenon.

CopperPrecipitate from the

solution by ore-extracted reductants

Remaining reductant

Cu precipitate


Control of Interfering Agents * Ion Exchangers: Usually consist of clays that exchange their

ions with the copper ions dissolved by reagents; thus, the metal remains in the gravel as a complex unlikely to re-dissolve

Those interfering compounds (or the possibility that they appear from the dissolved species) are identified by means of mineralogy and preliminary tests, and are controlled through: oxidation (reductants) or by pre-impregnation with ions with no value (exchangers) or by the adoption of unfavorable conditions to silicate dissolution, to avoid further formation of silicates.

* Complex Silicates: Complex compounds formed during leaching, starting from previous dissolution of silicates, which form colloidal compounds with similar properties to those of the ion exchanging clays, able to fix cations and previously dissolved copper.


The Redox potential is highly significant in sulphide leaching. It also controls the mineral reductants and iron oxidation states in oxide mineral leaching, and thus determines the type of secondary compounds they form. For example, within a reductant environment, the iron will be in ferrous state and will not form colloidal precipitates from hydroxides or from jarosites, and will not interfere in the ore bed porosity.

Identification of the Redox Potential as a Driving Force in Leaching.

In case of an oxidizing environment, the acid consumption increases to keep the ferric ions in the solution; however, it appears the risk of jarosite formation, which can affect the ore bed porosity as well as diffusion inside its own particles.


The ferrous to ferric oxidation in low acidity environments, has the capacity to return free acid to the system and reduce its consumption.


Terral uses diverse mechanisms for air injection, for addition of reagents, and for irrigation and resting pulses to activate the oxidizing mechanisms and the change of state of jarosites, to affect positively the leaching metallurgical results and develop specific leaching techniques:

Also the controlled formation of jarosites represents a mechanism to abate impurities in a virtually permanent form to control its concentration in the solutions, provided that once this compound is formed, its structure can be changed from the “gel” colloidal state to the permeable “sol” state.


Sulphide Leaching Bacteria-assisted leaching techniques use the mechanisms associated to their activity to generate ions and conditions for sulphide leaching. Given the large extent of this topic and abundant bibliography available, we will not present it in this opportunity.


Cleaning of precipitation solutionsTerral has developed an alternative process based on the recirculation of the precipitation ferrous solutions to the irrigation of the exhausted gravel, in order for oxidizing and precipitating the ferric ions to recover up to about 85% of the water with purity compatible with leaching.


Acid generation.The high price and consumption of some minerals encouraged Terral to incorporate sulphur to oxidize it in heaps to sulphuric acid.This research is at an initial promisory stage, still solving the issue on bacteria adaptation to changing environments in the heap, due to the recirculation of the leaching solutions to adjust the copper concentration in the PLS, based on the “TLM” concepts.


Leaching of Gold and Other Metals in Acid Environment.Upon inclusion of oxidizing ions in leaching, to reach gold oxidizing potentials and to supply the anions that can keep the ore in solution within an acid environment, recoveries of around 80% have been achieved from samples containing 3 gr gold/MT (and 0,6 % total copper, in mixed ores), verifying gold recovery from the solutions through any of the existing techniques. Also, the response of other metals to this same methodology is being explored.


Control of the PLS Characteristics The “irrigation ratio” is a leaching driving force, which activates the physical-chemistry of dissolution. An interpretation in terms of a countercurrent extraction unit operation, infers the possibility of adjusting the concentration of species at will, by means of recirculations.In copper: conditioned by recovery, kinetics, and recirculations. It is independent from the heap height and the irrigation rate, provided that the other factors have been adjusted; the cycle durations remains as a variable depending from all of them.In acid: conditioned by the controlled acid contribution from different sources and by the mineral consumption during the PSL generation stage, by irrigation with recirculation and with raffinate until reaching the “irrigation ratio”. In impurities: conditioned by the controlled acid contribution, by redox environments, by iron and jarosite handling, and other chemical complexes.


Control of the PLS Characteristics RECOVERY AND CONCENTRATIONS

VS. IRRIGATION RATIO

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Rec. Col. Modeled Rec. Mod. 15g/l Acid Cons. Col. Mod. Acid Cons. Mod. 15g/l

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Terral-Estudios N

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“Transtec” Proposal (Technological Transfer) “Transtec” is a business proposal consisting of:

* Terral evaluates a leaching operation, assuming the corresponding costs and risks; determines the applicability of its “TLM” methodologies and evaluates the prospective improvements and their economical value. Delivers a report to the company on the results obtained, but not on the used methodologies.* If the results are interesting; Terral will submit a “Transtec” program, which implies the transference of its methodologies under confidentiality terms, and the development of all the required tests - to be charged to Terral. Protocols state that the implementation of the methodologies will take place once the company’s success criteria have been satisfied.* At the same time, it is agreed on:- the objective forms of measurements of the results obtained,- the partition of the resulting benefits between the Company and Terral, and- the validity period of the agreement.* The program is approached under the compromise that the modifications will only affect the leaching processing aspects and will have minimum effect on the plant implementation; thus, there will be practically no new investments.


Maintenance of Clean OrganicAn impure PLS may induce contaminate the organic with micelles, which affect the separation times of the phases and increase the tendency to “crud” formation. The operational strategy turns to maintaining the organic phase as clean as possible, by means of a preventive treatment over an organic flow, parallely to the circuit in the normal operation.

Novelties in Solvent Extraction Topics on Processes

Use of Impregnated Extractant in Inert Substrate The mixer-settlers are not adequate to recover elements with concentrations within the ppm range.Terral has started tests with a 100% pure extractant impregnated in an inert porous medium to apply the operational concepts and unitary processes of the ionic exchange resins, in order to recover the elements under such conditions.


Configuration of SX Equipment Mixers:

Crossing bafflesbetween boxes


* Terral adopts permanent changes in the direction of the phases’ flows that gradually separate in settlers; the phases move separately both horizontally and vertically from the interphase.

Configuration of SX Equipment

* The concept on specific flows is modified and becomes “apparent” , while the real settling surface becomes larger when distributed both vertically and horizontally.

* The real specific flow becomes substantially smaller than the “apparent” one, and also changes into specific for each of the phases as they can adjust to a longer vertical path, to favor settling of the phase that should be recovered cleaner.



Settlers:

Picket fences

RecirculationsLaunder w/windows and baffle

Coalescence Baffles



After-Settlers

Flotation Chamber flotación

Coalescence Baffles

Accumulation Zone


Configurations of SX Equipment Organic Tank

Baffles and Coalescence MediaIncoming

Chamber

Water Collection Tank

Pumping Chamber



Electrolyte Filters


Agitated and Ventilated Cell.This cell shows the characteristics to improve the technical, economical and environmental performance of the electrowinning process.

Novelties in Electrowinning

The development and design objectives are:* To operate at very high current densities, up to 600 Amp/m2,

to reduce the considerable investment required in this plant section.* To produce better quality cathodes than those obtained under conventional current densities, due to evident market reasons.

* To solve the maximum operational problems to facilitate the operations performed during electrowinning.

* To solve problems caused by acid mist, to improve the environment

and reduce the tankhouse corrosion* Allow update of the existing cells, which will be easier if this technology is implemented in an existing unit

* To combine with other operations, so that it is possible to comply with the new electrolyte feed requirements, and to transfer the benefits gained in this cell to other sections.


Agitated and Ventilated Cell


Agitated and Ventilated Cell Electrolyte to over flow box

Inlet for sparging air

Electrolyte Inlet

Electrolyte to slugs blowing

Suction of Electrolyte with slugs


Agitated and Ventilated Cell Inlet andcell level adjustment

Narrow Weir flowmeter

Oulet chamber External

discharge pipe

Siphon Pipe (Internal-External)


Descenso(Al tapar la única celda abierta)

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Time (min)

Agitated and Ventilated Cell

novedades en lixiviación, extracción por solventes y electro-obtención; intermín; antofagasta;...

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