a toheexc. ThandSMrtinbe

The introduction of lance technology has enabled the use of sta-tionary furnaces of simple design and very

ses intth inhp submto comtralia iDeveloand cd commnal lice

slag bath. The use of advanced process control systems results inthe furnace operation being largely automated. Being a vertical fur-nace, a very small footprint of oor space is required to accommo-date the plant and so it can generally be easily retro-tted intoexisting smelters to either augment or replace existing technology.The process concept is shown in Fig. 1.

ments have occurred in areas such as furnace design, feed prepara-

Mount Isa Mines Ltd. Testwork was also performed for AGIP Aus-tralia Pty Ltd., who owned the Radio Hill deposit in Western Aus-tralia Bakker et al. (2009). In 1991, AGIP decided to construct asemi-commercial ISASMELT plant to produce nickelcoppermatte from concentrate feed. This was the rst ISASMELT plantbuilt and commissioned for an external client. Earlier in 1991,the rst commercial-scale ISASMELT plant had been commis-sioned to produce lead bullion from concentrates in Mount Isa. Ayear later, two commercial-scale ISASMELT plants were commis-sioned to produce copper matte from concentrates; one in MountIsa and the other in Miami, Arizona.

Corresponding author.

Minerals Engineering 24 (2011) 610619

Contents lists availab

Minerals En

elsE-mail address: mbakker@xstratatech.com.au (M.L. Bakker).combined annual smelting capacity exceeding 9,000,000 tonnesof feed.

2. The ISASMELT process

ISASMELT technology is based on a furnace design which isreadily enclosed to eliminate emissions to the surrounding envi-ronment. It uses submerged lance injection technology to providehighly efcient mixing and reaction of feed materials in a molten

have been licensed to date.

3. Agip nickel ISASMELT plant

It is less well known that the ISASMELT process was alsoadapted for the treatment of nickel bearing feeds at a very earlystage of its development. A large amount of pilot-scale testworkwas completed during the 1980s on nickel deposits owned byprior art involved the injection of gapredominantly through tuyeres, witions and refractory problems. The tosmelting technology was developedMount Isa smelting complex in Aussubsequently called ISASMELT.has focussed on smelting of leadsecondaries over the last 30 years annaces operated by Xstrata and exter0892-6875/$ - see front matter 2010 Published bydoi:10.1016/j.mineng.2010.09.016high reaction rates. Theo liquid slags or matteserent design complica-erged lance (TSL) bathmercial success at then the early 1990s, andpment of the processopper concentrates orercial ISASMELT fur-nsees currently have a

tion systems, off-gas handling, operating and process controlstrategies, refractory management and operator training. The com-bined experience led to what is well recognised by the marketplacetoday as the ISASMELT technology package, a technology pack-age licensed to external clients Burford (2009). Many of theimprovements implemented by plant operators have been passedonto, and adopted by, other licensees. Exchange of ideas and tech-nical improvements occurs through ad hoc visits to fellow licenseesites and through regular licensee workshops arranged by XstrataTechnology. Fig. 2 shows the location of the commercial plants thattechnology on large scale plants, signicant technical improve-ISASMELT TSL Applications for nickel

M.L. Bakker a,, S. Nikolic a, P.J. Mackey baXstrata Technology, Level 4, 307 Queen Street, Brisbane 4000, Australiab PJ Mackey Technology Inc., Kirkland, Quebec, Canada

a r t i c l e i n f o

Article history:Available online 25 October 2010

Keywords:Extractive metallurgyPyrometallurgySulde oresOxide ores

a b s t r a c t

The ISASMELT process isoped and optimised over tSMELT technology willsmelters around the worldconverting nickel mattes,the features that make ISAnickel smelting and convefrom recent pilot plant and

1. Introduction

journal homepage: www.Elsevier Ltd.p submerged lance (TSL) bath smelting technology which has been devel-last 25 years. By the end of 2011, the total installed capacity of the ISA-eed 9,000,000 tonnes per year of feed materials in copper and leade technology is equally effective for smelting nickel sulde concentrates,producing ferronickel from lateritic ores. This paper demonstrates howELT attractive for copper and lead smelting may be applied equally tog operations. Conceptual owsheets are presented, supported by resultsnch-scale testwork.

2010 Published by Elsevier Ltd.

During 30 years developing and operating submerged lancele at ScienceDirect

gineering

evier .com/ locate/mineng

EngiM.L. Bakker et al. /MineralsThe AGIP nickel ISASMELT commercial-scale plant was com-missioned in September 1991 and within 3 months was runningat design capacity of 7.5 t/h concentrate Arthur and Hunt(2005). It produced 45 wt% nickel/copper matte from a concen-trate containing approximately 7 wt% nickel and 3.5 wt% copper.Photographs of the plant are shown in Fig. 3 Bakker et al.(2009). At the time, the plant was deemed a technical and opera-tional success, however due to a large drop in nickel price, thefacility was forced to close near the end of 1991; the plant hassince been demolished.

Fig. 1. The ISASME

Umicore

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FreeportMiami

SouthernPeruCopper

MopaniCopperMines

Doe RunPeruCopper

BRM

YCC Chambishi

UmicoreFreeportMiami

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KEY: retlemSreppoCyramirP

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Primary Nickel Smelter

KEY: retlemSreppoCyramirP

retlemSreppoCyradnoceS

Primary Nickel Smelter

KEY: retlemSreppoCyramirP

retlemSreppoCyradnoceS

Primary Nickel Smelter

Fig. 2. ISASMELTneering 24 (2011) 610619 6114. The ISACONVERT process

A combination of pilot plant copper and nickelcopper continu-ous converting trials and the commercial batch copper convertingoperations show the ISASMELT furnace to be well suited to theduty of continuous converting the ISACONVERT furnace Ed-wards and Alvear (2007).

The ISACONVERT technology is based on the same design asthe ISASMELT furnace which allows it to be readily enclosed toeliminate emissions to the surrounding environment. It uses the

LT concept.

Mt Isa Mines CuMt Isa Mines Pb

ubis

Yunnan Copper

Vedanta

Kazzinc CuKazzinc Pb

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Mt Isa Mines CuMt Isa Mines PbVedanta

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YMG Qujing

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plant locations.

IP n

612 M.L. Bakker et al. /Minerals Engisubmerged lance injection technology to provide highly efcientmixing and reaction of solid matte and ux, which is dropped inthrough the roof of the furnace. As with the ISASMELT furnacethe ISACONVERT has a small footprint of oor space and can gen-erally be easily retro-tted into existing smelters.

The union between recent applied research and pioneering pilotplant work has made possible the industrial-scale implementationof the ISACONVERT process Nikolic et al. (2009). A cutaway im-age of an ISACONVERT plant is shown in Fig. 4.

Application of both the ISASMELT and ISACONVERT furnacetechnology to copper production allows for a very compact sitethat requires signicantly less area than a conventional coppersmelter. The fact that the smelting and converting processes arevery similar and easy to control via a proven robust process controlsystem also simplies operations and logistics within the smelter,allowing all operations to be carried out from one central control

Fig. 3. Photographs of AGroom. These factors lower the operating costs of a new smeltercompared with the conventional PeirceSmith technology. The sig-

Fig. 4. Cutaway of a design for the ISACONVERT furnace.nicantly reduced off-gas volume from the ISACONVERT processwill result in lower capital and operating costs for off-gas collectionand cleaning systems.

5. Nickel ISASMELT sulde smelting process concept

The feed to a nickel sulde smelter typically consists of a nick-elcopper concentrate, which may also contain minor amounts ofcobalt and platinum group metals. The smelting product from suchfeeds is generally a primary, high iron smelting matte which is fur-ther processed, typically in PeirceSmith converters, to producenished, high grade matte, often referred to as Bessemer matte.

The 2007 TMS survey of worldwide nickel sulde smelters re-ported that ash smelting accounted for approximately 70% ofnickel smelter output (based on 20042005 reporting data), with

ickel ISASMELT plant.

neering 24 (2011) 610619electric furnace smelting representing the balance Warner et al.(2007). However, the same features that make the ISASMELTprocess an attractive alternative for copper and lead smelting canbe equally applied to nickel smelting Bakker et al. (2009).

The basic process block diagram for a primary smelting nickelISASMELT plant is shown in Fig. 4. The nickel ISASMELT fur-nace continuously processes concentrate feed, uxes, and recycleddust. The product liquid matte and slag is tapped periodically fromthe ISASMELT vessel to a separate slag cleaning furnace via a sin-gle taphole. Off-gases from the ISASMELT furnace are directed toa waste heat boiler for heat recovery and de-dusted using an elec-tro-static precipitator before being sent to a sulfuric acid plant forsulfur capture. The primary smelting matte is transferred by ladlesfrom the settling furnace to the PeirceSmith converters for pro-duction of Bessemer matte; alternatively continuous convertingcould be used, refer below. Discard slag is also intermittentlytapped from the settling furnace for disposal. All dusts collectedfrom the gas handling systems are recycled to the ISASMELTfurnace.

The possibility of using the nickel ISASMELT process to pro-duce Bessemer matte with low iron content directly from concen-trate feed is also shown in Fig. 4, as a dotted line. This wouldobviate the need for PeirceSmith converting altogether. The directnickel ISASMELT process is similar to the Direct OutokumpuNickel (DON) process where the metal values in the smelting slagare recovered in the slag cleaning furnace. The DON process wasrst applied to the Harjavalta plant in Finland in 1995 and then

at a much smaller scale at the Fortaleza plant in Brazil in 1998 Mkinen and Taskinen (2006). The nickel ISASMELT thus hasthe exibility to produce either primary smelting matte (Fe inmatte greater than 15 wt%) or Bessemer matte (Fe in matte lessthan 4 wt%) depending on the customers requirements.

6. Nickel ISACONVERT process concept

Matte generated from the primary smelting of nickel concen-trate is almost exclusively processed to Bessemer matte using mul-tiple units of PeirceSmith converters. The exceptions are theAnglo PlatinumWatervale smelter in South Africa, where the AngloPlatinum Converting Process (ACP) is employed and StillwaterMining Company smelter in Montana, USA, where top blown ro-tary converters are used. In both cases, the respective convertingprocesses treat granulated primary smelting matte, however, ofthe two, only the ACP is fed continuously.

Continuous nickel converting is not a new concept and has beeninvestigated previously for improved productivity and emissioncontrol compared to the traditional PeirceSmith batch converters.As noted above the ACP plant has already commercialised the basicprocess concept. In addition, Vale Inco has for over a decade carried

basic process block diagram for a nickel ISACONVERT plant isshown in Fig. 5. It should be noted that the nickel ISACONVERTprocess is a truly continuous converting process with matte andair/oxygen continuously fed to the bath. The bath consists of theconverting products at all times, as the operating conditions effec-tively x the process at what is, for PeirceSmith converters, theend point of the converting reactions.

The nickel ISACONVERT furnace continuously processes pri-mary smelting matte feed, uxes along with recycled slag cleanermatte and dusts. The product liquid Bessemer matte is tapped peri-odically from the matte taphole to: (1) A granulation system or, (2)Slow cooling system (depending on renery). Slag is tapped from aseparate taphole from the ISACONVERT vessel to a separate slagcleaning furnace where metal values are recovered by addingreductant (coke and/or concentrate) to produce a separate matteand a cleaned slag phase. The matte from the slag cleaning furnaceis granulated and recycled to the ISACONVERT furnace, whereasthe slag is discarded. Off-gases from the ISACONVERT furnace aredirected to a waste heat boiler for heat recovery and de-dustedusing an electro-static precipitator before being sent to a sulfuricacid plant for sulfur capture. All dusts collected from the gas han-dling systems are recycled to the ISACONVERT furnace.

The presented nickel ISACONVERT process offers two impor-

Liquid Slag Cleaning/ ToReductant Matte

M.L. Bakker et al. /Minerals Engineering 24 (2011) 610619 613Clean Slag

MatteSettling Furnace

Bag

Offgas

+ Dust

StackDust

RefineryFlux

Offgas

Discardout a substantial research and development program investigatingcontinuous nickel converting Warner and Diaz (2003). Overabout this period, Vale Inco investigated three approaches for con-tinuous converting; their own ash converting (Victorovich(1993)), oxygen top blowing-nitrogen bottom stirring bath con-verting technology, and using Noranda/El Teniente type bath con-verting technology (Donald et al. (2005)). It is noted that theprimary goal in this work was to develop a continuous convertingtechnology applicable for the Copper Cliff, Ontario nickel plant,where downstream rening requires a very low, 0.5 wt%, iron inmatte. While technically feasible, in the tests (Donald et al. 2005)the more oxidized slag produced at this low iron content provedsomewhat problematic; instead preference was given to a two-stage approach involving continuous converting to about 23%Fe, followed by batch nishing for nal matte grade adjustment.

It is in the production of Bessemer mattes, down to less than4 wt% iron, where the ISACONVERT is seen to have a niche. The

OffgasWHB

Nickel

ISASMELT

Furnace

Air

Oxygen

Fuel

Offgas

+ Dust

ESP

Slag + Matte

Concentrate

Stockpile StackAcid

Plant

Peirce Smith

Converter(s)

Offgas

Bessemer

Slag toISASMELT/

Slag Cleaning/Settling Furnace

Air Flux

Dust

Recycle

FluxCoal

Dust RecycleFilterRecycle

Fig. 5. Process block diagram for a nickel ISASMELT plant.tant advantages compared with the traditional batch PeirceSmithConverting.

The rst advantage of the ISACONVERT process is the genera-tion of a constant volume of high strength SO2-containing gasesthat can be treated in a conventional sulfuric acid plant. This isan important benet considering current and future stringent envi-ronmental regulations affecting both plant emissions and in-planthygiene. While tting tight converter hoods remains the option tomaintain adequate SO2 levels in converter off-gas, this approachcoupled with the additional need for secondary hooding to controlfugitives emissions all add to the overall cost of PeirceSmith con-verters. The ISACONVERT offers a one-step converting processthat can utilize high levels of oxygen enrichment coupled withminimal air dilution, thus producing a lower volume off-gas readilyamenable to treatment in a sulfuric acid plant.

A second advantage is the exibility offered by the use of solidmatte as the feed material, thus eliminating ladle transfers, and

Dust

Recycle

OffgasWHB

Nickel

ISACONVERT

Furnace

FluxCoal

Dust Recycle

Clean Slag

Air

Oxygen

Fuel

Cleaner Matte

ESP

Slag

Matte

Stockpile

Slag Cleaning

Furnace

Bag

Filter

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+ Dust

Stack

Stack

Recycled to

ISACONVERT

Bessemer

Matte

Acid

Plant

Matte

Granulation/

Slow cooling

To

Refinery

Reductant

Flux

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Offgas

Discard

Dust

Offgas

+ DustRecycle

Fig. 6. Process block diagram for a nickel ISACONVERT plant.

further lowering opportunities for fugitive emissions with theresulting improvement in-plant hygiene. Further, the use of so-lid/granulated feed allows decoupling of the smelting and convert-ing steps, giving added exibility and simplies the maintenanceand operational aspects of the smelter.

7. Nickel ISASMELT laterite smelting process concept

The 2007 TMS survey of worldwide nickel laterite smelters re-ported that the Rotary Kiln-Electric Furnace technology (RKEF) isalmost exclusively used for the smelting/reduction of nickel-bear-ing laterites Warner et al. (2006). The RKEF process typicallytreats a low-iron magnesiumaluminiumsilicate saprolite mate-rial (or sometimes a transitional material); the electric furnace(EF) products are a ferro-nickel alloy for the market (after rening)and a discard slag. In some cases, sulfur is added at the reductionkiln, thus producing a low sulfur matte at the EF which is nishedto a Bessemer matte by conventional converting. The ISASMELTtechnology has recently been investigated for the smelting of thesetype of nickel laterite ores.

The basic process block diagram for a nickel laterite smeltingISASMELT plant is shown in Fig. 7. The ISASMELT furnace con-

An alternative option to this owsheet involves the addition of a

The main objectives of these tests were to determine the prod-

and collecting the materials in cast iron ladles. The process off-

Nickel MatteSlag Cleaning/

Settling FurnaceFlux Refinery

614 M.L. Bakker et al. /Minerals EngiClean Slag

Bag

Filter

Offgas

+ Dust

StackOffgas

Discard/

Heat Recovery

Dusttinuously processes dried laterite feed and recycled dust, with thesmelting heat provided by coal and oxygen-enriched air; ux addi-tion may be considered depending on the ore used. The product li-quid alloy and slag are periodically tapped via a single tapholefrom the ISASMELT vessel to a separate slag settling/cleaning fur-nace. Alternatively the ISASMELT furnace can be used for smelt-ing/pre-reduction, maximising fuel energy usage, with themajority of the reduction, and therefore nickel alloy generation,completed in the slag cleaning furnace. Another variation wouldbe to include a calcination step, for example, using a ash calcinerbefore the ISASMELT unit. ISASMELT off-gases can be post-combusted in the upper section of the furnace (with the additionof some oxygen-enriched air as required), imparting heat to theincoming feed. Off-gases from the top of the ISASMELT furnaceare then directed to a waste heat boiler for heat recovery and de-dusted using an electro-static precipitator before being sent tothe site stack. The product liquid ferro-nickel alloy is periodically

OffgasWHB

Nickel

ISASMELT

Furnace

FluxCoal

Dust RecycleFeSx/S

Air

Oxygen

Fuel

Offgas

+ Dust

Laterite

Ore Stockpile

Acid

Plant

Ferro Nickel Alloy/

Slag +

Alloy/MatteReductant To

Offgas Stack

Dust

RecycleDryer

ESPRecycle

Fig. 7. Process block diagram for a nickel laterite ISASMELT plant.gases are cooled and de-dusted before being directed to a causticsoda scrubber for removal of any sulfur-containing gases prior toventing to stack.

8.2. Nickel ISASMELT smelting trials

Nickel concentrates were successfully smelted to producemattes over a wide range of iron contents; from 1.6 wt% Fe to20.0 wt% Fe. The purpose of the testwork was to demonstrate theprocess exibility for the production of matte at any grade requiredby the customer, ranging in composition from primary smeltinguct nickel matte/alloy and slag compositions, elemental partitionratios between matte/alloy and slag (particularly nickel and co-balt), and generate slags for subsequent slag cleaning testwork.

8.1. The ISASMELT pilot plant

The pilot ISASMELT facilities consist of a stationary cylindricalfurnace with an internal diameter (within refractory) of approxi-mately 400 mm and a height of approximately 2000 mm. The ves-sel is lined with chromemagnesite refractory bricks, and is backedby high alumina insulation bricks. During operation, the furnacecontains a molten bath having a maximum depth of about600 mm. Controlled amounts of air and oxygen are injected intothe bath via either a 32 mm (1.25 inch) or 38 mm (1.5 inch) stain-less steel lance. The feed is added in known amounts to a calibratedvariable speed conveyor belt which drops the feed through a chuteat the top of the furnace at a rate typically between 100 kg/h and250 kg/h. Fuel oil is injected down the lance to control bath tem-perature. In some cases, solid coal may also be added. Removalof molten products can be achieved by opening one of two tapholessulfur-bearing feed (refer to dotted lines and process units inFig. 6), that can be added to the ISASMELT furnace bulk feed toallow for the production of a low-iron matte.

8. Nickel ISASMELT pilot plant trials

Several more recent campaigns of trials using an ISASMELTpilot plant have been conducted to provide further data regardingthe operability of the:

(i) ISASMELT process involving the smelting of nickel/copperconcentrates to either a high iron primary smelting matte orBessemer matte;

(ii) ISACONVERT process involving the converting of primaryhigh iron smelting nickel/copper matte to Bessemer matte;and

(iii) ISASMELT process involving the smelting of nickel lateriteores to a ferro-nickel alloy, involving both pilot and bench-scale tests.tapped from the electric furnace to: (i) A granulation system, or(ii) A casting system (depending on product specications), or(iii) A hot metal ladle for further rening as needed. Discard slagis also intermittently tapped from the settling furnace for disposal;and advantageously if required, heat recovery. All dusts collectedfrom the gas handling processes are recycled to the ISASMELTfurnace.

neering 24 (2011) 610619matte (Fe in matte greater than 15 wt%) to Bessemer matte (Fe inmatte less than 24 wt%) from feed concentrates. The typical nick-el/copper concentrate feed composition is shown in Table 1.

The concentrate was pelletised with pre-determined amountsof silica ux (according to the planned slag composition) and

Fluid slags were produced under all test conditions. The ironsilica ratio in ISASMELT slag generated during the tests rangedfrom 0.9 to 1.4. Compositional ranges for the ISASMELT slag forthe tests are shown in Table 2.

The distribution coefcients for nickel, as dened by Eq. (1) be-low, are shown as a function of iron content in bulk matte in Fig. 7,both for the ISASMELT and ISACONVERT tests (discussed laterin the ISACONVERT trials section). The bulk matte and slag wereanalysed from spoon samples taken during tapping.

Ls=mX wt% in slag=wt% in matte 1Included in Fig. 7 for comparison are the laboratory results of

Henao (2003) and the results obtained during a sampling cam-paign of a PeirceSmith blow on nickel-copper matte at the XstrataNickel (XNi) Falconbridge smelter (Bustos et al. (1988)) and at theVale Inco Thompson smelter (Diakow et al. (1975)). In Henaoswork, a matte-slag melt was equilibrated at 1500 C or 1600 Cfor a given time period at a specic xed oxygen (Po2) and sulfurdioxide (Pso2) atmosphere (set by S2/SO2 and CO/CO2 ratio control).At the end of each equilibrated test, quenched samples of matteand slag were taken for assay. The XNi Falconbridge and Vale IncoThompson smelter data were obtained by sampling the matte andslag in the converter at the end of each individual blow. Interest-ingly, all the data in Fig. 7 compare very well.

The distribution coefcients for cobalt, as dened by Eq. (1), are

Table 1Nickel/copper concentrate feed composition.

Element Average content (wt%)

Ni 17.1Cu 4.3Co 0.4Fe 31.0S 27.0SiO2 9.8MgO 6.5Al2O3 1.0CaO 0.7

Table 2Range of ISASMELT slag compositions.

Element Range (wt%)

Ni 0.87.0Cu 0.31.5Co 0.20.3Fe 32.037.6SiO2 25.634.9MgO 6.710.3Al2O3 3.85.1CaO 1.42.5

M.L. Bakker et al. /Minerals Engineering 24 (2011) 610619 615charged to the furnace at a rate equivalent to 150 kg/h of wet con-centrate. Granular coal was typically added to the feedbelt at a rateequivalent to 5% of the concentrate feedrate to provide additionalsmelting heat, due to the heat loss term associated with the sizeof the pilot-scale furnace. Smelting air and oxygen were meteredthrough separate rotameters at a ratio to yield 4045 v/v% totaloxygen. Fuel oil was injected down the lance as trim fuel to main-tain the bath temperatures between 1310 C and 1450 C, depend-ing on the test conditions.Fig. 8. Nickel in slag as a functionshown in Fig. 8 as a function of the iron content of matte for theISASMELT and ISACONVERT tests. Included in Fig. 8 for com-parison are the laboratory results of Font (1999) and, as perFig. 7 the industrial data from Bustos et al. (1988) and Diakow etal. (1975). In Font (1999)s work, a matte-slag melt was equili-brated (as in Henao (2003)s later work noted above) for a giventime at a specic xed oxygen (Po2) and sulfur dioxide (Pso2)atmosphere (set by S2/SO2 and CO/CO2 ratio control). At the endof each test, quenched samples of matte and slag were taken forassay.of iron in ISASMELT matte.

ncti

616 M.L. Bakker et al. /Minerals Engineering 24 (2011) 610619The XNi Falconbridge and Vale Inco Thompson smelter datahere were obtained by the same method as described for Fig. 7.

Fig. 9. Cobalt distribution as a fuAs with Fig. 7, it is of interest to note that all data in Fig. 8 for cobaltdistribution between slag and matte compare very well.

Figs. 7 and 8 shows that with decreasing iron levels in matte,both the nickel and cobalt slag/matte distribution coefcients in-crease. This is as expected due to the higher oxygen potential(Po2) of the system associated with lower iron levels in matte. Fur-ther as noted, the data in Figs. 7 and 8 shows that there is goodagreement between the pilot plant results for both the ISASMELTand ISACONVERT trials and previously published data for some-what similar matte-slag systems.

In order to provide information on the slag liquidus tempera-tures for slags encountered in the pilot plant trials, the FactSage(Bale et al. (2002)) package was used to evaluate phase equilibriain the NiOMgOFeOFe2O3SiO2Al2O3CaO slag system. The re-sults of the FactSage calculations at the conditions of:Po2 = 107.6 atm, Al2O3 = 4 wt%, CaO = 1.5 wt% and MgO = 10 wt%are shown on the pseudo-ternary NiOFeOSiO2 diagram inFig. 9. The FactSage liquidus calculations and slag compositionsfrom the pilot trials were plotted by normalising to the axes ofthe pseudo-ternary graph. It can be seen that all slags encounteredin the tests were predicted to lie within the olivine primary phaseeld (p.p.f.).

Table 3Primary smelting nickel matte composition.

Element Average content (wt%)

Ni 44.5Cu 9.7Co 2.9Fe 25.3S 17.2SiO2 0.38.3. Nickel ISACONVERT trials

on of iron in ISASMELT matte.The purpose of the converting testwork was to demonstrate theISACONVERT process for converting solid high iron primarysmelting matte feed to low iron Bessemer mattes. The typical pri-mary smelting matte composition is shown in Table 3. As will beshown, the primary smelting mattes were successfully convertedto produce nished mattes with iron contents from 2.2 wt% Fe to9.6 wt% Fe.

In the tests, matte with a pre-determined amount of high silicaux (set according to the target iron to silica ratio in slag) wascharged to the furnace at a rate equivalent to 200 kg/h of as re-ceived solid matte. Granular coal was added to the feedbelt at arate equivalent to 5% of the matte feed rate, due to similar consid-erations as mentioned in pilot-smelting. Converting air and oxygenwere metered through separate rotameters at a ratio to yield 3540 v/v% total oxygen enrichment. As with the smelting tests, fueloil was injected down the lance as trim fuel to maintain the bathtemperatures between 1310 C and 1380 C depending on the testconditions.

It was found that uid slags were produced under all test con-ditions over a range of ironsilica ratios in ISACONVERT slagfrom 1.1 to 2.3. Compositional ranges for the ISACONVERT slagfor the tests are shown in Table 4.

Table 4Range of ISACONVERT slag compositions.

Element Range (wt%)

Ni 2.26.4Cu 0.61.2Co 1.32.5Fe 37.848.0SiO2 25.634.9

As noted above, the level of nickel in slag and the slag/matte co-balt distribution coefcient for the ISACONVERT tests are in-cluded in Figs. 7 and 8. The nickel ISACONVERT tests aimed toachieve low iron content in matte. As evident in Fig. 7, the Ni levelin slag rises signicantly towards the low Fe matte composition.On account of the more oxidized conditions at low iron levels inmatte, the slag under these conditions has a higher liquidus. How-ever in this case, the Fe/SiO2 can be trimmed to lower the liquidustemperature.

As with the smelting tests, the FactSage (Bale et al. (2002))package was also used for the converting conditions to predictthe liquidus temperatures in the slag system using the simpliedNiOFeOFe2O3SiO2Al2O3CaOMgO system. The predictionswere projected, through normalisation of the data, onto the pseu-do-ternary NiOFeOSiO2 system in Fig. 10. The following condi-tions were used for the FactSage calculations: Po2 = 107.6 atm,Al2O3 = 2.5 wt%, CaO = 1.5 wt%, and MgO = 2.5 wt%. The composi-tions of the nal ISACONVERT slags are plotted together withthe liquidus predictions in Fig. 10. Similar to the ISASMELT slags,most of the ISACONVERT slags were within the olivine primaryphase eld (p.p.f.).

8.4. Nickel laterite ISASMELT trials

the bath was reduced with the addition of coal over time. Due tothe preliminary nature of the tests, a ux high grade silica and/or limestone was added to the ore to ensure the formation of aliquid slag. It is recognised that in practice, uxing would not nor-mally be carried out. For the pilot-scale trials, the laterite ore withsilica and limestone ux were charged to the furnace at a rateequivalent to 150200 kg/h of ore. Solid coal was added to thefeedbelt for both reduction and to provide a portion of the requiredsmelting energy. The balance of the heat to maintain the moltenbath was supplied by fuel oil injected down the lance.

It was found that uid slags were produced under all test con-ditions; the compositional ranges for the slags for both the bench-

Table 5Nickel laterite feed compositions.

Element Bench-scale testwork Pilot-scale testworkAverage content (wt%) Average content (wt%)

Ni 0.61.8 0.33.6Fe 5.025 8.420.9SiO2 2246 4046MgO 1225 1222Al2O3 2.58.5 0.73.0CaO 0.11.1 0.22.5

M.L. Bakker et al. /Minerals Engineering 24 (2011) 610619 617The purpose of the laterite smelting testwork was to demon-strate the production of a ferro-nickel alloy at both the benchand pilot-scale. The campaigns were undertaken on two separatelaterite deposits that were not related by geographical location.The typical compositional ranges for the two laterite ores usedfor the work are shown in Table 5. These laterite ores were success-fully smelted in the tests under reducing conditions to produce aferro-nickel alloy and a low nickel slag. The bench-scale trials pro-duced ferro-nickel alloy grades between 15 and 40 wt% Ni with astarting SiO2/MgO and Fe/Ni ratios between 1.23.1 and 1020respectively. On the other hand, the pilot-scale trials produced fer-ro-nickel alloy grades between 60 and 85 wt% Ni with a startingSiO2/MgO and Fe/Ni ratios between 2.03.6 and 512 respectively.

The bench-scale tests were carried out batch-wise in small cru-cibles (holding approximately 1 kg of melt). After initial melting,Fig. 10. Liquidus in the system NiOFeOSiO2Al2O3CaOMgO at Poscale tests and the pilot-scale trials are shown in Table 6.The trend of weight percent nickel in slag as a function of time,

as the coal was added to the crucible melt, in the bench-scale testsis shown in Fig. 11. The bench-scale trials were targeted to achieveselected ferro-nickel grades, whilst at the same time producing lownickel contents in the slag. It was also found that the nickel level inslag was highly affected by the settling time. Operating tempera-ture and ux addition can be optimized to minimise the settlingrequirement and maximise ferro-nickel alloy recovery.

The FactSage (Bale et al. (2002)) package was used to predictthe liquidus temperatures for the laterite smelting slag condi-tions. The simplied FeOFe2O3SiO2Al2O3CaOMgOCr2O3 sys-tem was used to represent these slags. Due to the low levelsof nickel oxide in the slag after reduction, nickel was not taken intoaccount in the FactSage calculations. The predictions were pro-jected, through normalisation of the data, onto the pseudo-ternary2 = 107.6 atm, Al2O3 = 4.0 wt%, CaO = 1.5 wt% and MgO = 10 wt%.

MgOFeOSiO2 system in Fig. 12. The following conditions wereused for the FactSage calculations: Po2 = 1011.1 atm, Al2O3 = 4.0wt%, CaO = 0.2 wt%, and Cr2O3 = 1.0 wt%. The range of laterite cruci-ble-scale and pilot-scale compositions for the ISASMELT slags areplotted as a grey circle togetherwith the FactSage liquidus predic-tions in Fig. 12. Depending on bulk slag composition and tempera-ture, the primary phase eld of the slag system in the highlightedregion can be pyroxene, olivine or tridymite/cristobalite (see Fig. 13).

9. Future development

Xstrata Technology has demonstrated to date that the ISA-SMELT process is an attractive option for both primary and sec-ondary copper and lead smelting. More than 9,000,000 tonnesper year of feed materials are processed in these ISASMELT fur-naces in copper and lead smelters at smelters around the world.The features that make ISASMELT attractive for copper and leadsmelting can be applied equally to nickel smelting and convertingoperations. The use of the ISASMELT process for copper/nickelsmelting has already been successfully demonstrated on a com-mercial scale.

Recent ISASMELT and ISACONVERT pilot and batch-scaletestwork described here has been successfully completed on the:

(i) ISASMELT process for producing primary high iron smelt-ing matte and Bessemer matte directly from concentrates;

(ii) ISACONVERT processes for production of Bessemer mattefrom high iron matte; and

Table 6Range of ISASMELT nickel laterite slag compositions.

Element Batch-scale testwork Pilot-scale testworkAverage content (wt%) Average content (wt%)

Ni 0.030.3 Fe 7.121 1825SiO2 3550 4450MgO 2027 1418Al2O3 5.06.9 2.63.3CaO 2.88.6 0.22.3

t Po

618 M.L. Bakker et al. /Minerals Engineering 24 (2011) 610619Fig. 11. Liquidus in the system NiOFeOSiO2Al2O3CaOMgO aFig. 12. Reduction of nickel from sla2 = 107.6 atm, Al2O3 = 2.5 wt%, CaO = 1.5 wt% and MgO = 2.5 wt%.g bath from Bench-scale testing.

3 at

M.L. Bakker et al. /Minerals Engi(iii) ISASMELT process for producing ferro-nickel alloys of var-ious grades from nickel laterite ores.

Future development of the nickel ISASMELT process may re-quire additional improvements to be made to the existing furnacedesigns. These include:

Fig. 13. Liquidus in the system FeOFe2O3SiO2Al2O3CaOMgOCr2O(i) Furnace cooling operation at temperatures above 1300 Cwill require furnace cooling systems to ensure sufcientlylong campaign life;

(ii) Tapping blocks tapping of nickel matte/alloy will requireimproved tapping block design;

(iii) Pneumatic injection exploitation of dry concentrate injec-tion through the ISASMELT lance to minimise fuel require-ments; and

(iv) Optimisation of the ISASMELT slag cleaning process tomaximise payable metal recoveries.

These development issues are currently being addressed.

Acknowledgement

The authors would also like to thank Xstrata Technology forpermission to publish this paper.

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ISASMELT TSL Applications for nickelIntroductionThe ISASMELT processAgip nickel ISASMELT plantThe ISACONVERT processNickel ISASMELT sulfide smelting process conceptNickel ISACONVERT process conceptNickel ISASMELT laterite smelting process conceptNickel ISASMELT pilot plant trialsThe ISASMELT pilot plantNickel ISASMELT smelting trialsNickel ISACONVERT trialsNickel laterite ISASMELT trials

Future developmentAcknowledgementReferences