JOM • July 200540

Copper and Nickel ProductionOverview

Table I. Summary of Operating Features for BioNICTM, Intec, Activox®, and CESL

Process Developer

Typical Feed

GradeGrind Size

(µm) Temperature

(ºC) Pressure Additives

BioNIC5 BHP Billiton

4–12% Ni

P80 = 75 30–40 atmospheric Dilute H2SO

4

and bacteria

Intec6

Nickel Process

Intec Ltd. 3–6% Ni P80 = 25 80–90 atmospheric Aeration, acid pre-leach, and mixed halide

leach

Activox7 Western Minerals

Technology

4–12% Ni

P80 = 10 100 1,000 kPa Oxygen gas

CESL8 Nickel Process

Cominco Ltd.

8–15% Ni

P90 = 45 150 1,380 kPA O2, HCl

Metal-market analysts project a global nickel supply gap which will be fi lled by further high-pressure acid leach treatment of laterite ores and the commercialization of hydrometallurgi-cal refi neries to recover nickel from sulfi de ores. The Activox® process is one such hydrometallurgical technology developed to recover a range of base and precious metals from sulfi de ores and concentrates. The combination of ultrafi ne grinding and oxidative leaching extracted and enabled the recovery of 96.2% nickel, 88.3% cobalt, and 82.9% copper in the 310 kg/h Tati Hydrometal-lurgical Demonstration Plant.

INTRODUCTION

The hydrometallurgical demonstra-tion plant (HDP) commissioned at Tati Nickel Mine in Botswana in 2004 is the culmination of seven years of R&D. The fi rst-of-its-kind hydrometallurgical process facility represents a signifi cant step in the commercialization of Western Minerals Technology’s (WMT’s) pat-ented Activox® process. The successful operation serves to reduce the technical and economic risk of installing a full-

The Activox® Process: Growing Signifi cance in the Nickel Industry

C.M. Palmer and G.D. Johnson

scale Activox refi nery and consolidate its position as a leading nickel sulfi de hydrometallurgical technology. This article examines the place of Activox in the nickel industry by considering several competitive hydrometallurgical process technologies.

THE CASE FOR HYDROMETALLURGY

It is only worthwhile to grow a business in markets that present strong demand. The global supply/demand picture for nickel metal tells an encouraging story for all those involved in the supply of nickel. Nickel demand growth averaged approximately 7% per year in 2003 and 20041 and is expected to increase by 4.1% in 2005.2 The current growth has been fueled by worldwide stainless steel production, rapid growth in China, and strong growth in industrial economies of the United States, Europe, and Japan.1 Scott Hand, chief executive offi cer of Inco Ltd., Toronto, Canada, in 2004 compared the current industrial produc-tion growth with the vigorous global industrial production growth driven by Japan in the 1960s.1 Chris Pointon,

president of BHP Billiton’s Stainless Steel Materials Customer Sector Group, in 2003 suggested that the nickel supply defi cit may be the result of combined high entry barriers and insuffi cient capital returns in the 1990s.3

Eleven nickel smelters are responsible for producing approximately 60% of the world’s nickel supply from nickel sulfide concentrates.2 Metal-market analysts project a global nickel supply defi cit, yet environmental and economic pressures suggest that there is unlikely to be a 12th nickel smelter.2,3 The nickel supply gap will be fi lled by further high-pressure acid leach (HPAL) treatment of laterite ores and the commercialization of hydrometallurgical refi neries to recover nickel from sulfi de ores. There is a global shortage of traditional nickel sulfi de refi nery feed stock4 and a number of hydrometallurgical processes are being developed to recover nickel and other base metals from lower-grade sulfi de concentrates. These hydrometal-lurgical processes share relatively low capital cost compared to smelting, are relatively environmentally friendly, and each claim high recoveries when treating a range of concentrates.

THE TECHNOLOGY RACE

Four hydrometallurgical technologies share a similar stage of development: Activox, BioNICTM, Intec Nickel Process (INP), and Cominco Engineering Ser-vices Ltd. (CESL) nickel process. Each process has produced nickel metal from sulfi de concentrates through the opera-tion of a pilot plant. These processes are compared herein with operating features summarized in Table I.

BioNIC

BioNIC employs bioleaching—the extraction of metals from sulfi de ores or

2005 July • JOM 41

concentrates using water, air, and micro-organisms. A typical stirred tank biole-aching system treats fl otation concentrate with no re-grind. Microorganisms exit the reactor with the residue and solu-bilized base metals requiring suffi cient microorganism growth rates to maintain the microbial concentration. Rorke et al.5 list the key factors to maintain rates of microbial growth: metal concentrations, nutrient addition, CO

2 addition, oxygen

supply, pH, temperature, presence of toxins, solids concentration, and agitator shear rate.5 In addition to microorganism growth there must be iron sulfi de spe-cies to provide a source of ferric ions. Gilbertson describes the process as “a ferric leach, with the re-oxidation of ferrous back to ferric, being catalyzed by microorganisms.”9 BioNIC was tested at a demonstra-tion facility at BPR in South Africa using ion exchange in 1996–199710 and later at Queensland Nickel’s Yabulu refi nery in Townsville, Queensland, Australia, using solvent extraction during 1998–1999.11Queensland Nickel decided to proceed with a plant at a scale of approximately 5,000 t/y nickel.

Intec Nickel Process

The INP incorporates membrane tech-nology, operates at atmospheric pressure and temperatures below 100°C, and uses a high-strength mixed halide circuit to treat bulk and low-grade nickel/copper/cobalt feed stock.6 The major differences between the INP and established smelt-ing-plus-chloride-leach processes are the Intec mixed halide electrolyte contains bromide as well as chloride and an acid pre-leach may be substituted for the smelting step.12

The ten-year development program of the generic Intec process has principally focused on the production of copper metal from copper sulfi de concentrates. Experience gained through a 350 t/y demonstration plant has confi rmed the commercial viability of the Intec Copper Process.6 A shorter development time for the INP is expected and promising test results have made the INP ready for testing on a demonstration scale.

CESL Nickel Process

Cominco Engineering Services Ltd. is a wholly owned subsidiary of Cominco Ltd., formed in 1992 in Vancouver to

treat copper sulfi des. The process has since been modifi ed to treat nickel and cobalt sulfi de concentrates. The CESL nickel process was developed in 1996 to treat Mt. Keith concentrates and involves the medium-temperature (150°C) and pressure (1,380 kPa) leaching of lightly re-ground fl otation concentrate in the presence of recycled acid and oxygen. A light regrind of the concentrate to 10% > 325 mesh (approximately P

90 = 45 µm)

increases the surface area of the feed and improves the reaction rate during pressure oxidation.8

Pilot testing of the CESL nickel process was conducted in 1996 and 2001–2003. A pre-feasibility cost esti-mate was carried out for a 1.1 million t/y bulk Ni/Cu/Co sulfi de concentrate refi n-ery using the CESL nickel process.13

The Activox Process

Activox is a hydrometallurgical pro-cess owned and developed by WMT for the oxidative leaching of sulfi de concentrates. The process incorporates ultra-fi ne grinding typically to a P80 of ~10 µm to activate the mineral surfaces (Figure 1), followed by a low-tem-

perature (100°C–110°C), low-pressure (1,000 kPa) oxidative leach to break down the sulfi de matrix. Base metals can then be recovered from solution while gold, silver, and platinum-group elements remain in the leach residue to be recovered by conventional treat-ment.14–17

WMT was formed in 1998 as a spe-cialist developer of hydrometallurgi-cal technology with a major focus on commercializing its patented Activox process. The shareholders of WMT are LionOre Mining International Ltd. (80%) and Aqueous Metallurgy Pty. Ltd. (20%). WMT has compiled a consider-able database of test results covering a wide range of different concentrates including nickel sulfi de ores, refractory gold ores, copper ores, and cobaltiferrous pyrite ores. Activox offers a number of mechanical and process advantages: • Mild conditions allow selective

oxidation of sulfi de minerals, and the formation of elemental sulfur instead of sulfate uses less oxygen

• Mild conditions allow quick shutdown and start-up

Figure 1. Three ultra-fi ne grinding mills.

Figure 2. Counter-current decantation.

JOM • July 200542

Table III. Reactions

Pentlandite

Nickel Extraction NiFeS2 +2H

2SO

4 + O

2 → NiSO

4 +FeSO

4 + 2H

2O + S

2

NiFeS2 + 4O

2 → NiSO

4 +FeSO

4

Cobalt Extraction CoFeS2 + 2H

2SO

4 + O

2 → CoSO

4 + FeSO

4 + 2H

2O + S

2

CoFeS2 + 4O

2 → CoSO

4 + FeSO

4

Copper Extraction CuFeS2 + 2H

2SO

4 + O

2 → CuSO

4 + FeSO

4 + 2H

2O + S

2

CuFeS2 + 4O

2 → CuSO

4 + FeSO

4

Pyrite

Iron Extraction FeS2 + O

2 → FeSO

4 + S

2Fe7S

8 + 14H

2SO

4 + 7O

2 → 14FeSO

4 + 14H

2O + 16S

2

Pyrrhotite

Iron Extraction 2Fe7S

8 + 14H

2SO

4 + 7O

2 → 14FeSO

4 + 14H

2O + 16S

2

Oxidation of Iron 4FeSO4 + 2H

2SO

4 + O

2 → Fe

2 (SO

4)

3 + 2H

2O

Production of Goethite and Acid 2Fe2 (SO

4)

3 + 8H

2O → 4FeOOH + 6H

2SO

4

refractory sulfi de gold concentrates,7 while its subsequent development has focused on treating poly-metallic base metal concentrates.14–17 WMT designed and constructed an Activox pilot plant in Osborne Park, Western Australia which has treated nickel/copper/cobalt concentrates from Yakabindie, Cosmos, and Emily Ann in Western Austra-lia; Nkomati in South Africa; Tati in Botswana; and Voisey’s Bay in Labrador, Canada. These campaigns demonstrate the viability of the Activox leaching tech-nology and a downstream process to produce nickel and copper metals and other saleable products showing the following extractions:

• >95% for nickel and cobalt • 75–90% copper • 40–80% S2- conversion to S0

The pilot plant is capable of treating a nominal rate of 20 kg/h; solution fl ow rates are typically 120 L/h into the downstream processes. The circuit includes ultra-fi ne grinding; autoclave leaching; iron removal; separate solvent extraction facilities for copper, cobalt, and nickel; counter-current decantation (CCD) (Figure 2) solid-liquid separation equipment; ammonia regeneration; and copper and nickel electrowinning (EW) facilities. See the sidebar for background on the Tati HDP.

INNOVATIVE ENGINEERING

The demonstration plant project won the Western Australia 2004 Engineer-ing Excellence Award for the Small Company Project and Overall category awards. The judging criteria included innovative plant design, sound engi-neering practices, and benefi t to the community.21

From the beginning, it was apparent that effi cient management of logistics would be the key to success. A distinction had to be drawn early in the design stage as to how far construction of the plant would progress in Perth before shipping it to and installing it in Botswana. The solution was a design that split the plant into modules conforming to process units, which were then laid out to fi t on 2.2 m wide steel skids for easy fi tting into standard sea containers (Figure 3). All plant modules were assembled in Perth, tested, and wet commissioned as far as possible before being disassembled and packaged by a crating company.22

Table II. Tati HDP Feed Grades; Target versus Actual for Run 5

Design Actual

Iron 33.60 46.2

Sulphur 21.70 30.1

Silica 12.29 3.64

Calcium 3.20 1.26

Magnesium 2.80 0.9

Nickel 4.22 4.2

Copper 2.53 1.71

Cobalt 0.127 0.07

Chromium 0.06 0.062

Manganese 0.05 0.018

Figure 3. The transpor-tation of the HDP in sea containers.

• Most of the iron precipitates selectively as hematite or goethite, which can be readily stabilized

• Recoveries of metals such as nickel, cobalt, and copper into solution exceed 95%

• Mild conditions allow the use of comparatively low-cost materials of construction

• Oxidation kinetics are relatively fast; reactions are essentially complete within 2 h, allowing more production per unit of equipment size

• Activox can operate with highly saline process water, and water contaminants that are detrimental to bacteria can be tolerated

The Activox process was originally developed in 1993 to recover gold from

Figure 4. The Tati HDP autoclave.

2005 July • JOM 43

Table IV. HDP Autoclave Performance Design versus Steady-State Operation

Unit Design Run 5

Feed Rate kg/h 310 230.6Acid Addition kg/t 42.6 50.8Absolute Autoclave Pressure kPa 1,100 1,099Compartment 1 Temperature °C 100–110 107.8Compartment 2 Temperature °C 100–110 108.8Compartment 3 Temperature °C 100–110 104.7Compartment 4 Temperature °C 100–110 108.6Compartment 5 Temperature °C 100–110 110.4Nickel in Autoclave Feed % 4.22 4.78Nickel in Autoclave Residue % 0.18 0.18Nickel Extraction % 95.6 96.2Copper in Autoclave Feed % 2.53 2.64Copper Extraction % 78.2 83.0

Process Overview

The HDP treats 310 kg/h Phoenix nickel rougher concentrate and produces London-Metal-Exchange-grade nickel and copper, and a cobalt carbonate pre-cipitate. A description of each process stage follows and plant performance will be discussed by comparing the target operating parameters to the per-formance data collected during fi ve days of a steady-state run number 5.23 Table II shows the difference between target and actual grade measured during run 5. High sulfur levels were common to most of the operation runs and caused consistently low throughput; feed rate was 25% lower than design in run 5 and sulfur levels were 35% higher.

Ultra-Fine Milling

The ultra-fi ne grinding of Phoenix rougher fl otation concentrate from 60 µm to 10 µm was carried out by one or two of three mills: the Bradken-Metprotech mill, Metso Minerals’ stirred media detritor mill, and Netszch’s IsaMill. Each mill conforms to common design bases: 500 kg/h concentrate, 50% solids, F

80 = 60 µm,

P80

= 10 µm, and power consumption = 45 kWh/t.23 The mills differ in such features as operating tip speed, media volume, and shell liner material. The Bradken-Metprotech Mill is vertically stirred with a high-aspect-ratio chamber; it has a 30 kW main motor drive. Other specifi cations include: operating tip speed: 2.5–3.0 m/s; media volume: 200 L; media: silica,

ceramic, or steel (2–4 mm); shell liner: metallic; and shaft and arms: metallic sleeves.23 The Netszch IsaMill is horizontally stirred, with a 37 kW motor, direct on line (fi xed speed). Other specifi cations are: operating tip speed: 10 m/s; media volume: 45 L; media: silica (2–4 mm); shell liner: nil; and shaft and disks: polyurethane.23 The Metso detritor mill is vertically stirred with a low-aspect-ratio milling chamber. Other specifi cations are: 18.5 kW motor, direct on line (fi xed speed); operating tip speed: 7.5 m/s; media volume: 100–200 L; media: silica, ceramic, or steel (2–4 mm); shell liner: natural rubber; and shaft and arms: polyurethane coated.24

Activox Leach

The fi nely ground feed for the auto-claves was diluted from 50% solids to 30% solids by the addition of copper

TATI HDP BACKGROUND The Tati hydrometallurgical demonstration plant (HDP) is adjacent to the existing con-centrator at the Phoenix mine site in Botswana. The Tati Nickel Mining Company (TNMC) is owned by LionOre Mining International (85%) and the Botswana government (15%).19

The TNMC Phoenix operation has been profi tably mined since 1996. The ore was ini-tially processed using dry magnetic separation techniques before a fl otation concentrator was commissioned in 2002 that produces 12,500 t payable nickel in concentrate per year. This nickel concentrate is sold to Bougainville Copper Ltd., an integrated nickel and cop-per concentrating and smelting operation located some 200 km from TNMC.19

The successful pilot operation of Activox using Tati’s Phoenix nickel concentrate be-tween 1998 and 2002 involved over 1,000 h of continuous piloting and led to the approval of $10.5 million for the construction and commissioning of the HDP. The development of the HDP represents scale-up ratio of 170. A defi nitive feasibility study on the construction of a full-scale commercial plant at Tati was completed in September 2003;20 this was a signifi cant stage in the commercialization of Activox. The aims of the HDP are to:

• Facilitate the training of operating and maintenance personnel• Optimize design and construction materials• Confi rm the economic viability of the Activox process at Tati• Showcase Activox to the mining industry19

• Demonstrate a complex hydrometallurgical process in Botswana

raffinate. The autoclave (Figure 4) operates at 100°C–110°C and absolute pressure of 1,100 kPa. The addition of 83 kg/h oxygen at pressure, 48 kg/t sulfuric acid to the autoclave feed, and 4 g/L chlorides in the form of a sodium chloride salt solution catalyze the oxida-tion of the sulfi de minerals as shown by the reactions in Table III.25

Leach extractions were consistently higher than design. Average leach recov-eries for runs four through six were 95% nickel, 88% copper, and 93% cobalt compared to the design extraction of 94% nickel, 78% copper, and 91% cobalt.20 The feed rate was frequently lower than design due to high levels of pyrrhotite; the extra sulfur affected the leach circuit by increasing the heat load, oxygen, and acid consumption.23 The autoclave feed rate was 320 kg/h when sulfur levels were at design levels. Table IV shows the autoclave performed in line with design despite the high pyrrhotite levels. The Activox autoclave proves to be simple to operate and reliable, with avail-ability at 93.5%. Starting and stopping the autoclave was straightforward with no need to cool the autoclave contents before depressurizing as it runs below the boiling point of the process liquor.25

The autoclave shell is constructed of Hastelloy C276; it is 3.9 m long (tan to tan) with an internal diameter of 1.04 m. The autoclave operates with 75% of 3.34 m3 fi lled and has a residence time of 2.6 h. The oxidation of sulfi de minerals under Activox conditions is exother-mic and heat is managed by vacuum fl ash cooling (VFC) on compartments one and two and the addition of direct quench (copper raffi nate) to compart-

JOM • July 200544

Copper PLS Tank

ments three, four, and fi ve. The VFCs operate at absolute pressure of 50 kPa and 83°C and operated 30% above the design heat load. The fl ash vessels are constructed of 2205 duplex steel lined with polyvinyl ester (corrocoat XT) with outside diameter of 0.757 m and length (tan to tan) of 1.827 m.24

The autoclave discharge slurry passes through the third fl ash vessel with the 30% solids residue rich in platinum group metals plus gold and free of valuable base metals (nickel, copper, and cobalt) and a sulfate solution containing valuable base metals: nickel, copper, and cobalt along with some iron, magnesium, manganese, calcium, sodium, and zinc. The HDP then follows conventional process circuits of solid/liquid separation, iron removal, solvent extraction, and EW according to the fl owsheet shown in Figure 5.

Counter-Current Decantation

The cooled autoclave discharge reports to thickener one of a seven-stage continuous counter-current decantation (CCD) circuit. The CCD circuit was designed to discharge 337 kg/h solids with thickener seven underfl ow density of 43% and the target soluble metal loss was 0.18% (116 ppm nickel soluble loss) with a wash water ratio of 3.0 kg/L and 95% wash effi ciency per stage.24

Underfl ow soluble metal grades fre-quently rose above design as wash water

was reduced to increase nickel. Grades at low autoclave throughput,23 however, were consistently under 100 ppm in the fi rst run in 2005. Flocculant SNF AN 920 is added at 200 g/t to thickener one and 40 g/t to thickeners two to seven. Thickener one is 2.0 m diameter, while thickeners two through seven are 1.6 m diameter with unit area requirement of 0.2 t/m2/h.24

Copper Solvent Extraction

The copper solvent extraction circuit operates with two extraction and two strip mixer settlers, one organic wash, and three after settlers (Figure 6). A

single mixing compartment per stage has a diameter-to-height ratio of 0.7 with 3.3 min. residence time. The settlers have dimensions of 1.6 m × 0.46 m; specifi c area is 4.6 m3/h/m2; and the organic space velocity is 1.03 cm/s at a depth of 0.1–0.25 m.24 In the extraction stage, the copper metal present in the PLS is recovered to the copper selective organic phase; 14% Acorga M5640 is dispersed within an organic carrier Shellsol D70. The copper solvent extraction circuit performs in line with design with strip effi ciency of 40% and extraction above 99%. Periodic phase disengagement problems (crud formation) occurred due

Figure 5. The Tati HDP Activox® process fl owsheet.

Figure 6. The HDP copper solvent extraction circuit diagram.24

2005 July • JOM 45

to the over fl occulation in the CCD circuit and the organic-to-aqueous interface level can be problematic to control on low-fl ow aqueous duty. The problematic interface is being overcome by operating with a higher organic inventory.

Copper Electrowinning

The EW circuit performs in line with a 146.8 kg/day design copper produc-tion: three polypropylene EW cells in series, each consisting of fi ve 316 SS blank cathodes of 1.16 m × 1.17 m; and six Pb/Ca/Sn alloy anodes in custom-designed anode bags.24

The EW process involves the applica-tion of a cell voltage of 2.2 V and cell current of 3,300 A (330 A/m2) to facilitate the reduction of copper to copper metal at the cathode and the oxidation of water at the anode. The sulfuric acid formed in this reaction is returned to the copper solvent extraction stripping circuit in the spent electrolyte and consumed in the stripping process. The copper metal is plated onto stainless steel cathodes which are periodically removed from the EW cell, stripped, and returned to the cell for further metal deposition. Guar gum dosing started in run three improved the cathode surface fi nish. Acid mist was eliminated through the use of WMT-designed anode bags (Figure 7). Iron removal is essential as the abun-dant iron present would cause unman-ageable fouling of downstream solvent extraction processes if not removed. The iron-removal process involves the oxida-tion of ferrous (Fe2+) iron in solution to ferric (Fe3+) iron and subsequent ferric iron precipitation as ferric hydroxide [Fe(OH)

3] and goethite (FeOOH). The

precipitation process relies on elevated temperature above 60°C and elevated pH of 3.5–5 in the presence of oxygen. The precipitation process is con-

ducted in two stages.25 Stage 1 operates at pH 3–3.5 and is designed to produce a disposable-quality iron precipitate; approximately 70% of the soluble iron precipitates in stage 1 with negligible co-precipitation of valuable metals. The product slurry from stage 1 is thickened, the residue is pumped to waste, and the overfl ow is pumped to stage 2. Stage 2 operates at pH 4–5 and is designed to produce iron-free liquor suitable for cobalt solvent extraction. The remaining 30% soluble iron is precipitated along with significant amounts of nickel, which demands the re-leaching of stage 2 thickener underfl ow while the stage 2 thickener overfl ow feeds the cobalt solvent extraction circuit.

Cobalt Solvent Extraction

The cobalt solvent extraction circuit operates three extraction and two strip mixer settlers, one organic wash, one diluent wash, and three after settlers. A single mixing compartment per stage has a diameter-to-height ratio of 0.7 with 4.4 min. residence time. The settlers have dimensions of 1.6 m × 0.46 m; specifi c

area is 1.8 m3/h/m2, and the organic space velocity is 0.40 cm/s at a depth of 0.1–0.25 m. The solvent system is 5% Cyanex 272 in 95% Shelsol D70.24 The cobalt solvent extraction cir-cuit (Figure 8) operated at pH 5.5 and extracted 98.8% cobalt in line with design parameters. Initial phase disengagement problems occurred due to the incorrect fl occulant selection in iron removal.

Cobalt Carbonate Precipitation

The cobalt carbonate precipitation circuit is a batch operation producing 9 kg/day cobalt as cobalt carbonate. The cobalt-rich loaded strip liquor from the solvent extraction circuit is transferred to the cobalt precipitation circuit where soda ash and steam are added to increase pH and temperature, respectively. Cobalt and impurity metals such as nickel, iron, and copper are precipitated to a solid carbonate product under elevated temperature and pH.

Nickel Solvent Extraction

The nickel solvent extraction circuit operates with fi ve extraction and two strip mixer settlers, two scrubbers, one organic recovery, and four after settlers. A single mixing compartment per stage has a diameter-to-height ratio of 0.7 with 4.4 min. residence time. The settlers are 1.6 m × 0.46 m with a specifi c area of 4.6 m3/h/m2 and organic space velocity of 0.40 cm/s at a depth of 0.1–0.25 m. The solvent system is 20% Versaitc 10 in 80% Shelsol D70.24

The nickel solvent extraction circuit operated at pH 6.5 and extracted more than 95% nickel in line with design

Figure 7. Anode bags in a copper electrowinning cell.

Figure 8. The HDP cobalt solvent extraction circuit fl ow diagram.25

JOM • July 200546

parameters. The nickel solvent extraction circuit fl ow is presented in Figure 9.

Nickel Electrowinning

The nickel electrowinning circuit comprised a series of six cells, each consisting of fi ve 316 SS blank cathodes of 1.16 m × 1.17 m, and six Pb/Ca/Sn alloy anodes in custom-designed anode bags. The circuit operated reliably by the end of the third cycle after overcoming some initial problems. Peeling of the starter-sheet blanks was overcome by minimizing changes to current settings and regularly cleaning cathode and anode contacts. The nickel circuit design included the following features: cell voltage: 3.2 V; design current density: 230 A/m2; cell current: 2,300 A; rectifi er consumption: 3,180 kW/t; operating temperature: 60°C; rich electrolyte grade: 80 g/L; and spent electrolyte grade: 50 g/L.24 The HDP produced nickel in line with the design 295 kg/d and the harvesting of 600 kg of commercial nickel cathode in August 2004 marked the fi rst nickel metal ever produced in Botswana.

Ammonia Regeneration

Ammonia regeneration is used in the demonstration plant to recycle ammonia from nickel and cobalt sulfate raffi nate solutions, reducing the amount of anhy-

drous ammonia required to maintain pH in the nickel and cobalt solvent extraction circuits. WMT developed an ammonia regeneration process involving the addition of quicklime to the ammonium sulfate solution in a vibrating reactor to liberate the ammonia. Ammonia is then recovered in a stripping vessel that is connected to a vapor condensation and scrubbing system.26

The demonstration plant reactor operates continuously up to 180 L/h and recovers 15–23% ammonia in solu-tion.

COMMERCIAL IMPLICATIONS

Environmental and economic benefi ts of hydrometallurgical technology are gaining attention in the mining industry. Development companies like WMT are investing resources in developing innova-tive process and engineering solutions to supply the expanding base metals market. In addition, the Activox process is attracting increasing interest from mining companies around the world, as demonstrated by pilot runs conducted for a large Canadian nickel producer and visitors to the HDP representing large international mining companies. The expansion of LionOre’s Activox and hydrometallurgical processing busi-ness has the potential to generate signifi -

cant profi ts and royalties to LionOre and its stakeholders. The feasibility study for developing the old Bulong nickel laterite plant into the Avalon Activox plant will be complete by the second half of 2005 and construction is expected to commence in late 2005. The Avalon feasibility study considers the design of 40,000 t/y nickel metal production.

CONCLUSIONS

The Tati HDP is realizing its objec-tives by: • Providing suffi cient data to

optimize design and construction materials

• Facilitating the effective training of operations and maintenance personnel

• Reducing the technical risk of installing a full-scale hydrometallurgical refi nery

• Showcasing the Activox process to the mining industry

• Demonstrating a complex hydrometallurgical process in Botswana

As developer and implementer of the Activox technology, WMT has increased its intellectual property in the operation and construction of hydrometallurgical processes at a time when hydrometal-lurgy is becoming a more fi nancially and environmentally attractive way forward

Figure 9. The HDP nickel solvent extraction circuit fl ow diagram.

in the processing of base metals. The success of the Tati HDP strength-ens the position of the Activox process and approval to build the 40 kt/y nickel Avalon Activox refi nery places Activox at the front of the nickel sulfi de hydro-metallurgical technology race.

References

1. S. Hand, (London: UBS, 8 June 2004), www.ubs.com. 2. Brook Hunt Nickel Metal Service (Surrey, England: Brook Hunt Consultants, January 2005), www.brookhunt.com/bhweb/cda/homepg.aspx.3. C. Pointon, “Stainless Steel Materials” (Melbourne, Australia: BHP Billiton Ltd., 3 February 2005), www.bhpbilliton.com/bbContentRepository/Presentations/SSMSAPresentationJune2003.pdf.4. Kalgoorlie Nickel Project Information Memorandum (Kalgoorlie, Western Australia, Australia: Heron Resources Ltd., 3 February 2005), www.heronresources.com.au/downloads/KNP.pdf.5. G.V. Rorke, P. Basson, and D.M. Miller, ALTA 2001 Nickel/Cobalt–7 Technical Proceedings (Melbourne, Australia: ALTA Metallurgical Services, 2005).6. J. Moyes and F. Houllis, ALTA 2003 Nickel/Cobalt–9 (Melbourne, Australia: ALTA Metallurgical Services, 2001).7. G.D. Johnson, I. Corrans, and J. Angove, Randol ’93 (Golden, CO: Randol, 1993).

8. D. Jones and R. Moore, ALTA 2002 Copper–7 (Melbourne, Australia: ALTA Metallurgical Services, 2002).9. B.P. Gilbertson, Mineral Processing and Extractive Metallurgy, 109 (2) (2000), pp. 61–67.10. D.M. Miller et al., Nickel/Cobalt 97 (Montreal, Canada: The Metallurgical Society of CIM, 1997).11. T. Heinzle, D. Miller, and V. Nagel, BioMine 99 and Water Management in Metallurgical Operations (Glenside, South Australia: Australian Mineral Foundation, 1999).12. “Intec Nickel Process” (Sydney, Australia: Intec Ltd., 30 March 2005), www.intec.com.au/html/Technology/Nickel.shtm.13. “The CESL Nickel Process,” (Vancouver, Canada: Cominco Engineering Services Ltd., 2004). 14. I.J. Corrans, J.E. Angove, and G.D. Johnson, Randol Gold Forum ’95 (Golden, CO: Randol International Ltd., 1995).15. H.A. Evans and G.D. Johnson, “Activox® Technology for the Treatment of Copper-Gold Concentrates” (Presentation at Oretest Colloquium ’99, 10 November 1999).16. G.D. Johnson, H.A. Evans, and J.H. Turner, Alta 2000 Nickel/Cobalt–6 (Melbourne, Australia: ALTA Metallurgical Services, 2000).17. M. Adams and G. Johnson, ALTA 2001 Nickel/Cobalt–7 (Melbourne, Australia: ALTA Metallurgical Services, 2001).18. O. Kloiber et al., ALTA 2005 Nickel/Cobalt–9 (Melbourne, Australia: ALTA Metallurgical Services, 2005).19. LionOre Mining International Limited 2003 Annual

Report (Toronto, Canada: LionOre, 2003).20. Hydrometallurgical Refi nery Defi nitive Feasibility Study (Perth, Australia: GRD MinProc, September 2003).21. “Engineering Excellence Awards Past Winners List” (Perth, Australia: Engineers Australia Western Australia Division, 30 March 2005), www.wa.engineersaustralia.org.au/engineering_excellence_awards/past_winners.shtml.22. “2004 Engineering Excellence Awards—Tat Hydrometallurgical Demonstration Plant” (Osborne Park, Australia: Western Minerals Technology, 2004).23. O. Kloiber et al., ALTA Nickel/Cobalt–9 (Melbourne, Australia: ALTA Metallurgical Services, 2005).24. “Tati Nickel Project: Hydrometallurgical Plant—Process Design Criteria” (Osborne Park, Australia: Western Minerals Technology, 26 October 2004).25. “Tati Demonstration Plant Project Operating Manual” (Osborne Park, Australia: Western Minerals Technology, 2004).26. G. Johnson and Y. Zhuang, ALTA 1999 Nickel/Cobalt Pressure Leaching and Hydrometallurgy Forum (Melbourne, Australia: ALTA Metallurgical Services, Melbourne, 1999).

C.M. Palmer and G.D. Johnson are with Western Minerals Technology Pty. Ltd. in Osborne Park, Australia.

For more information, contact C.M. Palmer, Western Minerals Technology Pty. Ltd., 1/45 Edward Street, Osborne, WA, 6017 Australia; +61-8-9444-2611; fax +61-8-9444-2715; e-mail cpalmer@wmt.com.au.

THEME: Light Metals

November 2005 Aluminum: Titanium: The Metal with Manuscripts Deadline: Cast Shop and Alloys the Bright Image August 1, 2005

THEME: Nanotechnology

December 2005 Carbon-Nanotube- Surface Engineering Manuscripts Deadline: Containing Material and Nanotechnology September 1, 2005

THEME: High-Temperature Resistance

January 2006 Materials for High-Temperature Superalloys and Coatings for Manuscripts Deadline: Protection High-Temperature Applications October 3, 2005

THEME: Energy Effi ciency

February 2006 Aluminum: Bauxite-Alumina- Metal Hydrides: Manuscripts Deadline: Carbon-Reduction The State of the Art November 1, 2005

THEME: Materials Characterization, Part I

March 2006 Neutron Scattering Applied Industrial Applications of Manuscripts Deadline: to Traditional Materials Problems Advanced Electron Microscopy December 1, 2005

THEME: Nanotechnology

April 2006 Nanostructured Materials: Nanoelectronics, Magnetics, Manuscripts Deadline: From Lab to Commercialization and Photonics January 2, 2006

THEME: Metals Fabrication

May 2006 Aluminum: Rolling and Recent Developments in History and Manuscripts Deadline: Extrusion Magnesium Production Archaeology of Materials February 1, 2006

T E C H N I C A L E M P H A S I S C A L E N D A R

UPCOMING EDITORIAL TOPICS

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