AU647898B2 - Bioleaching of cobalt and copper containing pyritic concentrates - Google Patents

Description

1 fi47RQR

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION 4' l FOR A STANDARD PATENT

ORIGINAL

Name of Applicant: 0 o0 Actual Inventors: o o 00 00 0 0 Address for Service: MOUNT ISA MINES LIMITED, A.C.N. 009 661 447 Mark Laurence Steemson, Gregory John Sheehan and David Arthur Winborne SHELSTON WATERS Clarence Street SYDNEY NSW 2000 "BIOLEACHING OF COBALT AND COPPER CONTAINING PYRITIC CONCENTRATES" Invention Title: Details of Associated Provisional Application No: PK5311 The following statement is a full description of this invention, including the best method of performing it known to us:- 1

C

i f i rir 2 The present invention relates to bioleaching of pyritic concentrates and in particular to bioleaching of cobalt and copper containing pyritic concentrates.

The invention has been developed primarily for use with cobalt containing pyritic concentrates and will be described hereinafter with reference to these materials, such as cobaltite and alloclasite. However, it will be appreciated that the invention is not limited to this particular field of use.

In the past, bioleaching has been known as a method of leaching a variety of concentrates. However, prior art methods of extraction have previously not been applicable to pyritic cobalt concentrates because cobalt is traditionally difficult to leach from the host minerals.

In accordance with the present invention there is provided a method of extracting cobalt by continuous microbial leaching of cobalt-containing pyritic concentrate comprising the steps of feeding a cobalt-containing pyritic concentrate feedstock into at least a first reactor unit, agitating and aerating the feedstock in the presence of microorganisms at a pH in the range of 1.2 to 2.5 and at a temperature in the range of 20 to 500C to produce a reaction product filtering the reaction product to recover cobalt.

In a preferred embodiment, there is provided a method of extracting cobalt by continuous microbial leaching of cobalt-containing pyritic concentrate wherein ,0\ t $1 (1r IL rL r L u- 3 the reaction product is fed to one or more reactor units including a final reactor unit at least one of the reactor units having means for agitation and aeration and recycling a reaction slurry product or a predetermined portion thereof to the first reactor unit wherein the reaction product from the final reactor unit is then filtered to recover cobalt.

The microorganisms may be a mixture of T. Ferrooxidans and L. Ferrooxidans. Preferably, the mixture is T. Ferrooxidans, L. Ferrooxidans and T. Thiooxidans. More preferably, the mixture includes T. Ferrooxidans, L. Ferrooxidans, T. Thiooxidans and mixed heterotrophic organisms. More preferably the temperature is 40 42 0

C.

Most preferably, the concentrate is cobaltite or I alloclasite in a pyritic background.

IIn a further aspect of the invention there is provided an apparatus for extracting cobalt from pyritic concentrates said apparatus including a series of reactor units including at least a first and final reactor unit, the first i and final reactor units including means for agitation and aeration; wherein feedstock is continuously fed into said first reactor unit and mixed in the presence of microorganisms at a temperature in the range of 20 to 0 C, at a pH in the range of 1.2 to 2.5 to produce a first reaction product; 4 the first reaction product continuously fed to at least a final reactor unit, for agitation therein to produce a final reaction product; a predetermined amount of the final reaction product recycled to the first reactor unit and the remainder of the reaction product filtered to recover the cobalt.

In a most preferred form the series of reactor units includes a first reactor unit, a final reactor and at least one intermediary reactor unit having means for agitation and aeration. In a preferred embodiment each reactor unit includes a medium of microorganisms at a temperature range of 200 to 50°C at a pH of 1.2 to In yet a further preferred form the microorganisms are a mixture of T. Ferrooxidans, and L. Ferrooxidans.

Preferably the mixture is T. Ferrooxidans, L.

i\ Ferrooxidans and T. Thiooxidans. Most preferably, the mixture is T. Ferrooxidans, L. Ferrooxidans, T.

Thiooxidans and mixed heterotropic organisms.

It was observed that the pH has a marked effect on I pyrite oxidation during bioleaching. The lower the pH i level, the more acidic, the higher bacterial i oxidation of the concentrate. The pH range is in the I range equal to or greater than 1.2 and equal to or less than 3.0. The preferred pH level for both chalcopyrite and cobaltite leaching is 1.5 2.0, a more preferred range is 1.5 1.7.

A further observation was the marked effect of m~m*l i 5 temperature on cobalt extractions. Higher temperatures led to improved cobalt recovery. The temperature is in the range equal to or greater than 20°C and equal to or less than 50"C. The preferred temperature level for cobaltite leaching in a pyritic background is 35-45 0 C, a more preferred range is 40-42°C.

The mixture of microorganisms is preferably a mix of multi-species population, such as a mix of T. Ferrooxidans and T. Thiooxidans, L. Ferrooxidans and mixed heterotrophic organisms.

Bioleach solutions contain a heavy contamination of iron (as ferrous and ferric ion) and arsenic in addition to cobalt (and copper or zinc if present) metal values.

In accordance with a further aspect of the present invention there is provided a method of extracting cobalt by continuous microbial leaching of cobalt-containing pyritic concentrate comprising the steps of: S:i) feeding a cobalt-containing pyritic concentrate feedstock into at least a first reactor unit, (ii) agitating and aerating the feedstock in the I, presence of microorganisms at a pH in the range of 00 1.2 to 2.5 and at a temperature in the range of to 50°C to produce a reaction product slurry, (iii) neutralizing the slurry to precipitate one or more impurities in a preferred form, (iv) removing the precipitate by filtration, oxidising further impurities to insoluble precipitates utilising an oxidant, 0._ i~l 4- I I~ i I-L -6- (vi) filtering the residual precipitate leaving a product liquor containing cobalt free of contaminants, (vii) recovering cobalt from the liquor.

In a preferred embodiment there is provided a method of extracting cobalt by continuous microbial leaching of cobalt-containing pyritic concentrate comprising the steps of: feeding a cobalt-containing pyritic concentrate feedstock into at least a first reactor unit, (ii) agitating and aerating the feedstock in the presence of microorganisms at a pH in the range of 1.2 to 2.5 and at a temperature in the range of to 50°C to produce a reaction product slurry containing cobalt, iron and arsenic, (iii) neutralising the slurry to precipitate ferric iron as ferric hydroxide and arsenic as ferric arsenate, (iv) removing ferric hydroxide and ferric arsenate by filtration, using unreacted pyrite and gangue present in the slurry to improve the filtration of a fine ferric hydroxide, i* oxidising any residual ferrous oxide to ferric iron with an oxidant, (vi) filtering the residual ferric hydroxide leaving a product liquor free of iron and arsenic, (vii) recovering cobalt from the product liquor.

Preferably copper is also recovered in step (vii).

Four examples of such recovery routes are given in SExample 4.

Ii ^-lil9llllii .Il_-LI 7 The preferred embodiment can be modified to recover part of the valuable metals (particularly copper) prior to step An example of this modification is given as Example In a preferred embodiment, hydrogen peroxide (H202), sulphur dioxide (SO 2 or air only may be applied as oxidants to remove ferrous iron in step The preferred reactions are: 2+ 3+ 2- 2Fe 2 SO 0 2Fe 3

SO

2 2 4 (using SO 2 2Fe 2 H202 2Fe 3 2H20 (using

H

2 0 2 or 2Fe 2 1/202 2H+--2Fe 3 (using oxygen or air) An appropriate pH the ferric iron will precipitate as insoluble ferric hydroxide.

Step (iii) can be conducted over a pH range of to 6 at temperatures of 25 60 0 C. However, to minimise copper losses and maximise iron precipitation, a pH range of 2.8 to 3 is preferable. Any appropriate neutralisation reagent in these steps can be employed, i _i I 7a although limestone or lime are both economically attractive and assist the filtration of products.

Step can be conducted over a pH range of 2.5 to 6 at temperatures of 25 to 60'C. If S0 2 /Air or hydrogen peroxide are used as oxidants, the conditions of oxidation are not critical, although copper losses can occur at pH levels greater than 3. If aeration only is to be used a pH range 4.5 to 5.5 is preferable, at i i

I

EL 8 temperatures of 40 0 C or higher.

Reaction times may be rapid (0.5 2 hours), resulting in small vessel sizes in a commercial plant.

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a graph of cobalt continuous bioleach temperature optimization at pH 1.6.

Figure 2 is a graph of copper continuous bioleach temperature optimization at pH 1.6.

Figure 3 is a graph of iron continuous bioleach temperature optimization at pH 1.6.

Figure 4 is a graph of cobalt continuous bioleach pH optimization at 40 0

C.

Figure 5 is a graph of iron continuous bioleach pH o" optimization at 40 0

C.

Figure 6 is a graph of copper continuous bioleach pH optimization at 40 0

C.

Tests were conducted on pyritic cobalt concentrates in the form of cobaltite and alloclasite using appropriate bacteria.

EXAMPLE 1 Conditions: Batch Scale; 1.5L solution. Slurries of up to 20% w/w solids Composition: Cobaltite (CoAsS), Alloclasite ((CoFe)AsS), Chalcopyrite (CuFeS 2 Pyrite (FeS 2 and Pyrrhotite (FeS) i 1 C 'I r' 9 Concentration: 0.1-0.3% Co as cobaltite or alloclasite 2-4% Cu as chalcopyrite Temperature: 20-35 0

C

pHi 1.4 2.3 Bacteria: Mixture of T. Ferrooxidans, T.

Thiooxidans, L. Ferrooxidans and mixed heterotrophic microorganisms Three materials were tested a) retreat tailings, b) pre-float concentrate (PFC) and c) cleaned PFC.

Table 1 Results: Material a) b) c) Co extraction 80-90% 90-95% 90-95% Cu extraction 65-75% 30-50% 80-90%

A

In the temperature range studied, little effect was noticed on the rate of copper extraction but 35 0 C was the optimum temperature for cobalt and zinc extraction.

Cobaltite, alloclasite and chalcopyrite are normally difficult to bioleach and the effect of galvanic interactions between the bulk pyritic background and low concentrate cobaltite, alloclasite and chalcopyrite has been used to enhance leaching effect and rate of extraction.

It was observed that the temperature range of 20-35 0

C

had little effect on the rate of copper leaching in batch tests.

I 1111~ 10 EXAMPLE 2

I

Conditions: Batch Scale: 160 L Composition: 0.3% Co as Cobaltite (CoAsS), Alloclasite and glauconite, 3% Cu as chalcopyrite (CuFeS 2 dominant mineral pyrite (FeS 2 subdominant iron mineral pyrrhotite (FeS) Temperature: 30 0

C

PH. 1.8 Bacteria: Mixture of T. Ferrooxidans, T.

Thiooxidans, L. Ferrooxidans and mixed heterotropic microorganisms.

Results: Co extraction: 94% Cu extraction: After 15 days batch testing (70% Co and Cu extraction after 3 days bioleaching.) Pilot Scale Batch Testina During the construction and commissioning phase of a continuous bioleach pilot plant, a 160L scale batch bioleaching test was conducted using pyritic cobalt feed. The test was conducted at 30°C, pH 1.8 with a w/w well aerated slurry over a 15 day batching period.

The bacterial charge used in the test was a mixture of Thiobacillus Ferrooxidans, Leptospirillum Ferrooxidans, Thiobacillus Thioxidans and mixed heterotrophic organisms adapted to the pyritic cobalt I I 11 t ,d 9 4 D4 4 t I o *8J 44 I material by upgrading the solids level from 5 to 20% over a three week period.

Most cobalt and copper leaching occurred within 4 6 days of test commencement. Final cobalt and copper extractions were 94% and 55% respectively. After 3 days, however, the bulk of copper leaching had occurred. This early leaching phase was due to enhanced leaching due to close pyrite-chalcopyrite galvanic interaction. After this, the copper leaching rate deteriorated rapidly. A similar, but less marked trend was found in the cobalt behaviour. The drop-off in extraction, however, could be attributed to the reduction in mineral surface availability.

In summary, larger scale batch testing indicates that good cobalt liberation and partial copper extraction was attained. Evidence is apparent of enhanced leaching effect due to galvanic pyrite interaction.

EXAMPLE 3 Conditions: Continuous Scale: 3 x 200L (160L working volume) bioreactors Feed rate: 65-150g/min of 20-25% slurry Residence time: 2.5-6 days overall (20-48 hrs/vessel) Bacterial type: A mix of T. Ferrooxidans, T. Thiooxidans, Feed material: L. Ferrooxidans and mixed heterotrophs.

3 sources of pyrite (FeS 2 )/cobaltite (CoAsS)/alloclasite ((CoFe)AsS)/chalcopyrite and final reactor units including means for agitation and aeration; S12 (CuFeS 2 )/pyrrhotite (FeS) [0.3 0.6% Co, 1.8 4.5% Cu, 20 30% Fe] EXAMPLE 3.1 Pilot Operation 3.1.1 Bioleach Train A pilot plant was designed and constructed as a proving stage to the development of a commercial continuous bacterial leaching process for cobalt production. Bioreactors were 200L (160L working volume) SS316 vessels fitted with variable speed mixing units and aerators. Mixing was achieved using 1 hp DC motor coupled to two 80mm, 3 blade propellers. Aeration for the bioleach trains was supplied by an oil free blower, capable of supplying up to 1200 L/min of air at 20 psig.

Each bioreactor was fitted with a 25mm SS 316 jacket coupled tc a recirculating water system for temperature control.

The cobalt bioleach pilot plant was a series of two continuous flow leach trains, each train operating as a cascade of up to three bacterial reactors.

In a single train, feed slurry was pre-aerated to lift slurry Eh levels to +400 mV (vs SHE). This pre-aeration was found necessary to prevent subsequent hydrogen sulphide generation. The slurry feed was then ;introduced to the first bioreactor continuously using a 25 peristaltic pump. The typical slurry density was solids. Feed to latter units occurred via the overflow (at the 160L mark) from the previous unit. The final reactor was fed to a collection vessel, with the contents r I 13 being periodically filtered after being neutralized to pH 2.8 3.0 for ferric iron removal. Part of the slurry contents of the final vessel were continuously recycled to previous units, the recycle rate varying with operating strategy. A small inocula was added to the first vessel on a semi-continuous basis.

3.1.2 Liquor Phase Inocula A liquid phase bacterial inoculator was operated on a batch basis separate from the operating bioleach train.

The batch inoculum served two purposes: To provide a steady supply of liquid phase bacterial which were introduced to the bioreactors on a semi-continuous basis. Such inocula were typically added at 3 4% of the feed slurry rate.

To maintain the bacterial population in case of j washout of the operating pilot trains and to Ithereby allow rapid reinoculation.

iThe liquid phase inoculator was a 200L scale batch reactor fitted with good aeration and temperature control facilities. The latter was enabled by the use of a 2 KW Incolloy heater. A 1% w/w solids addition was used to adapt the bacteria to pyritic substrate. Typically, the inoculator operated at pH 1.6, 40 0 C with 10 gpl Fe and 1 gpl Cu in solution. The iron and copper were maintained using periodic additions of fresh ferrous sulphate (Fe 2 +)/copper sulphate solution.

3.1.3 Slurry Filtration Following slurry neutralization to precipitate The following statement is a full description of this invention, including the best method of performing it known to us:-

I

W- i 4 14 u Pr Sp,

PP

p Ppt o~ P

IOI

p. 0 0s3 pa solution ferric onto the tailings solid surface, product solution was recovered via filtration. Four SS304 pressure filters were utilized on a batch basis. No major filtration problems were normally encountered, unless high ferric levels (>30 gpl/Fe3+) led to fine ferric hydroxide precipitate in solution.

3.2. Bioleach Optimization Tests During the course of continuous bioleach trials,samples of pyritic feed were inoculated with bacteria present in the pilot plant (a mixture of T. Ferrooxidans, L. Ferrooxidans, T. Thiooxidans and Heterotrophs) to determine the optimum pH and temperature. This optimization was determined using well aerated batch (1.5L scale) tests operating for up to 7 15 days at controlled temperature and pH. This procedure, by using bacterial present in the continuous pilot plant, provided rapid feedback as to optimal pH and temperature for continuous bioleaching.

Figures 1 to 3 present solution assay results for cobalt, copper and iron at temperatures in the range 35 0 C. The pH was maintained at 1.6 using powdered limestone additions. The optimal temperature for cobaltite and pyrite leaching was 40 45 0 C, preferably 0 C. The chalcopyrite optima was 45 50 0 C, preferably 50 0 C. These trials were conducted using flotation pyrite concentrate assaying 0.54% Co, 4.5% Cu and 32% Fe.

A further series of trials with varying pH levels using pyrite concentrate were conducted at a constant IL. -1 ieacning or coDait-containing pyritic concentrate wnerein i i0 II 15 temperature of 40 0 C. Figures 4 to 6 show the bioleaching behaviour from pH levels of 1.2 to 1.8 (in increments of pH 0.1).

Tests were again conducted using continuous pilot plant bacterial culture over a 6 day batching period. At 0 C, the optimal pH range for bioleaching was pH 1.5 1.7 for cobaltite, pH 1.5 1.6 for pyrite and pH 1.5 to 1.8 for chalcopyrite.

The preceeding trials were similarly repeated at a latter stage of continuous pilot plant testwork. The latter results gave simile" optima of 40 0 C and pH 1.5 1.7.

3.3 Continuous Test Results Continuous pilot plant trials were conducted on three cobaltite and chalcopyrite pyritic feedstocks: Copper Concentrator Reverse Flotation Pyrite a Copper Concentrator Pre-Flotation Concentrate (PFC) and a Cleaned (or re-floated) PFC. The trials were monitored until steady state operation was obtained (determined from chemical leaching data).

Table 2 summarizes the overall extractions obtained using the three feedstocks operated over a range of overall residence times (2.5 6 days). At 4 days residence time (30 hrs/vessel) cobalt recoveries were 25 81% depending on the amount of pyrite and cobaltite present in the feed material.

I TABLE 2 Cobalt Bioleach Pilot Plant Extraction Results Feed Overall Operating Re-cycle Head Grade(%) Overall Resi- Temp (OC) Extractions dence Time (days) Co* Cu Fe Co Cu Fe Reverse 6 40 20 0.54 4.5 32 84 23 44 Flotation 4 42 50 0.62 2.0 32 81 28 27 Concentrate 3 42 20 0.61 2.6 31 64 28 Cleaned Pre- 4 41 50 0.42 1.9 27 75 24 Flotation 3 40 50 0.38 2.7 30 70 23 17 Concentrate Pre- 6 40 50 0.30 1.8 25 75 25 24 Flotation Concentrate *mixture of cobaltite and alloclasite L 17 3.4 Key Continuous Plant Concepts The following key concepts were determined from continuous pilot plant trials to maximise cobalt extraction from pyritic feedstocks.

The use of galvanic interaction to enhance the bioleaching of both cobaltite and chalcopyrite Enhanced leaching of cobaltite using multiple bacterial populations An optimization of continuous bioleach temperature and pH conditions for the leaching of cobaltite, alloclasite and chalcopyrite from pyritic feedstocks The use of slurry recycle and a separate inoculator to enhance biological numbers in cobaltite or chalcopyrite leaching The use of Eh measurements as a process control/bacterial viability measure SThe use of a number of continuous leaching vessels in series to leach cobaltite, alloclasite and chalcopyrite Feed slurry conditioning using Eh control to I prevent biocide production EXAMPLE 4 Cobalt and Copper Recovery from Bioleach Product Liquors Scale: 1.5L of bioleach product slurry at 20% w/w solids Temperature: 40 0

C

18 Stage 1: Ferric Neutralization A 1.5L sample of bioleach product slurry was agitated at 40°C. Over a 1 2 hour period, powdered limestone (<75 um) was added to the slurry to adjust the pH gradually to pH 3. The initial solution was at pH 1.67, assaying at 1.4g Co/kg of soln, 2.3g Cu/kg, 19.9g Fe/kg and 2.9g As/kg. At pH 3 (after neutralization), the solution assayed at 1.5g Co/kg, 2.3g Cu/kg, 3.7g Fe/kg and less than 10 ppm As. All the residual iron was ferrous iron (Fe2+).

o° The limestone consumption was 27 kg of limestone/tonne of slurry.

Stage 2: Ferrous Removal using Oxidants 0 i S* Samples of ferric neutralized liquor were filtered 15 and the filtrate collected. Two ferrous removal schemes were trialed using 1.5L of separate samples: one using hydrogen peroxide (H 2 0 2 after 30 minutes of aeration, the other employing S0 2 /air. The results are presented in Tables 3 and 4. Both tests were performed at pH 3 using limestone as an acid production neutralizing agent. Using both schemes, a substantially iron free liquor was obtained, retaining the cobalt and copper in solution. No arsenic was measured in the final liquors.

Stage 3: Cobalt and Copper Recovery from Iron Free Liquors A number of recovery schemes have been developed to 1 t-91UJ- J. l3 .LOt.. 1 IC. UV 1 .11 J-CJ 1 V LI.) Four examples of such recovery routes are given in *Example 4.

19 recover copper and cobalt from iron free bioleach liquors. Four such routes are presented by way of example.

Case 1: Solvent Extraction of Copper/Oxidative Chlorination of Cobalt Copper was extracted using a suitable commercial organic extractant (10% LIX 984 diluted with Escaid 110 in this example) from a pH 3 bioleach liquor assaying at l.lg Co/L, 1.2 Cu/L and 25 ppm Fe. After a single extract phase at a total organic to aqueous ratio of 1:1, the copper was reduced to ppm. The final raffinate contained all of the cobalt and iron. Copper in the organic was removed by contact with 200 gpl H 2

SO

4 to produce a liquor suitable for copper electrowinning.

The de-copperized bioleach liquor contained appreciable quantities of calcium and magnesium in addition to the cobalt values.

An oxidative chlorination was employed to remove cobalt from these impuraties according to the reaction: 2Co 2 C12 6H20 -2Co(OH) 3 +201 6H L

I

LJ.L 'eC U C) L.A. L L 1 -Y neutralisation reagent in these steps can be employed, -p 20 TABLE 3: The Use of Hydrogen Peroxide for Ferrous Removal from Bioleach Liguors

H

2 0 2 Addition Metal Concentration (as a stoichiometric (ci/L) ratio to the initial Fe 2 level) CO Cu Fe 2 Initial 1.4 2.8 After 30 minutes of aeration 1.14 1.4 1.4 stoic H 2 0 2 1.14 1.4 0.50 0.9 stoic H 2 0 2 1.14 1.4 0.13 1.3 stoic H-202 1.13 1.4 0.01 TABLE 4: The Use of S0 2 -/air for Ferrous Removal from Bioleach Liauors (0.1 L/L min of 4% S0 2 in air, 400C) Time Metal Concentration (mins) (alL) CO Cu Fe 2 0 1.13 1.26 2.53 1.12 1.28 0.43 1.10 1.23 0.03 1.08 1.22 0.02 1.08 1.24 0.01 0' A

EL

i- Case 2: 0 00 0000 0 00 000 0 0 Do 60 0 00 00 C *0 00 0 0 000 0 0 00 21 At 40 0 C and pH 4.0, using twice the stoichiometric requirement of chlorine, over 99% cobalt recovery was obtained. The chlorine was added as sodium hypochlorite solution, containing 10% available chlorine.

The final dried cobaltic oxide solid product assayed at 41% cobalt.

Direct Oxidative Chlorination Ferrous removed bioleach liquor assaying 1.13g Co/L, 1.45g Cu/L was subjected to direct oxidative chlorination at pH 3 using five times the stoichiometric requirement of chlorine to the cobalt present. Testwork was performed at 40 0 C. The cobalt recovery was 97% with the final dried product assaying at 32% Co and 3% Cu.

The final liquor (containing copper) was a suitable feed to a copper solvent extraction or iron cementation plant after the cobaltic oxide product was filtered. This recovery route has advantages in minimizing capital expenditure, but does entail some copper loss.

Selective Precipitation of Cobalt and Copper Bioleach liquor at a similar initial concentration as that of Case 2 was neutralized to pH 6 at 40 0 C using sodium carbonate (Na 2

CO

3 to precipitate any copper present.

Case 3: 22 A blue copper carbonate product was formed which was readily filterable. The dry precipitate assayed at 36% Cu, 2% Co and contained 97% of the copper and 6% of the cobalt.

After filtration of the copper product, the liquor was subsequently neutralized using sodium hydroxide to pH 8.6. The final dried precipitate assayed at 30% Co, 0.7% Cu and contained 98% of the remaining cobalt. Both products contained less than 3% gypsum.

Case 4: Production of a Cobalt Hydroxide as suitable feed to a Cobalt Electrowin Plant A sample of de-copperized bioleach liquor (post copper solvent extraction in Case 1) assaying l.lg Co/L was neutralized to pH 8.6 at 40 0 C using commercial grade hydrated lime. All of the cobalt was removed from the liquor. The final dried solids precipitate assayed 10% Co (as cobaltous hydroxide (Co(OH) 2 with the bulk of the remaining precipitate being gypsum. Lime consumption was 4.6 kg of lime/kg of cobalt in solution.

The solids product produced using lime precipitation is an ideal feed to a cobalt electrowin circuit, whereby the cobaltous hydroxide is redissolved at solution levels of greater than 30g Co/L and then tests.

-23 electroplated onto stainless steel cathodes.

In this example, lime was used as a neutralization agent, owing to its economic advantages. However, sodium carbonate or caustic soda are equally effective.

EXAMPLE Recovery of Copper Prior to the Production of a Cobalt Hydroxide Product Scale: 200cc of ferric neutralised bioleach liquor (as per Stage 1 of Example 4) assaying at 2g Co/kg, 2.3g Cu/kg, 2g Fe/kg (all as ferrous) with a pH of Stage 1: Solvent Extraction of Copper As per Case 1 of Example 4, copper was extracted using 10% LIX 984 diluted with Escaid 110. After a jsingle 10 minute contact at an organic to aqueous ratio of 1:1, the copper was reduced to less than 30 ppm. The final raffinate contained all of the cobalt and iron.

Copper in the loaded organic was removed by contact with 200 gpl H2SO 4 to produce a liquor suitable for copper i electrowinning.

Stage 2: Ferrous Iron Removal using Air Oxidation The de-copperized bioleach liquor contained appreciable amounts of ferrous iron in addition to the cobalt values. This ferrous would both contaminate the final product and increase neutralisation agent usage.

L 24 The ferrous iron was removed by oxidative aeration at pH 5 and 40 0 C for up to 90 minutes in a well mixed, baffled, well aerated reaction vessel. The results are presented in Table 5. The pH was controlled at 5 using limestone or 2M H 2

SO

4 additions.

i Using this scheme, the ferrous level was reduced to less than 40 ppm in 60 minutes. Overall cobalt losses, based on solids precipitate assays were This cobalt can be partially recovered by recycling the solids residue to the bioleach stage.

TABLE 5: The Use of Oxidative Aeration for Ferrous Removal from De-copperized Neutralised Bioleach Liquors 40 0

C)

i Time Metal Concentration (q/L) (mins) Co Fe 2 0 2.16 1.90 2.32 0,171 60 2.35 0.039 90 2.48 0.001 Stage 3: Production of a Cobalt Hydroxide Product A final cobalt hydroxide product can be produced by neutralising the product liquor from the ferrous removal stage (after filtering and recycling the solids precipitate produced) to a pH 9 using a suitable alkaline agent (for example caustic soda, lime or ammonia). In this example, caustic soda was employed.

25 In a typical experiment, caustic soda was added to an agitated reactor containing post ferrous removed bioleach liquor, and the pH adjusted to 9.0. The final solids product was filtered from the residual liquor, dried, and assayed. With a pH 5, 40 0 C ferrous oxidation for 90 minutes, a final dry cobalt product was produced assaying at 22 33% Co. The caustic usage was 1.4 to 2.8 kg caustic/kg cobalt precipitated, the caustic usage depending on the level of zinc co-precipitated with the cobalt.

Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other

Claims (24)

1. A method of extracting cobalt by continuous microbial leaching of cobalt-containing pyritic concentrate comprising the steps of feeding a cobalt-containing pyritic concentrate feedstock into at least a first reactor unit, agitating and aerating the feedstock in the presence of microorganisms at a pH in the range of 1.2 to 2.5 and at a temperature in the range of 20 to 50'C to produce a reaction product and filtering the reaction product to recover cobalt.

2. A method in accordance with Claim 1 wherein the reaction product is fed to one or more reactor units including a final reactor unit to produce a final reaction slurry product which is then filtered, at least one of the reactor units having means for agitation and aeration, and wherein a portion of a reaction slurry product from one or more of the reactor units is recycle to the first reactor unit.

3. A method in accordance with claim 1 or 2, wherein the microorganisms include a mixture of T. Ferrooxidans and L. Ferrooxidans.

4. A method in accordance with claim 3 wherein the mixture includes T. Ferrooxidans, L. Ferrooxidans and T. Thiooxidans. A method in accordance with claim 3 or 4 wherein the mixture includes T. Ferrooxidans, L. Ferrooxidans, T. Thiooxidans and mixed heterotrophic organisms. d 4 4* 4 *r 4 I ,iil 27

6. A method in accordance with any one of claims 3 to wherein the temperature is 40 420C.

7. A method in accordance with any one of claims 1 to 6 wherein the concentrate is cobaltite, chalcopyrite or alloclasite in a pyritic background. i 8. A method in accordance with claim 7 wherein the pH Sis 1.5

9. A method in accordance with claim 7 wherein the pH is 1.5 1.7. A method in accordance with any one of claims 7 to 9 wherein the temperature is 35 450C.

11. A method in accordance with any one of claims 7 to 9 wherein the temperature is 40 420C.

12. An apparatus for extracting cobalt from pyritic concentrates said apparatus including a series of reactor f units including I at least a first and final reactor unit, the first and final reactor units including means for agitation and aeration; i wherein feedstock is continuously fed into said first reactor unit and mixed in the presence of i microorganisms at a temperature in the range of 20 to 50 0 C, at a pH in the range of 1.2 to 2.5 to produce a first reaction product; the first reaction product continuously fed to at least a final reactor unit, for agitation therein to produce a final reaction product; 28 an amount of the final reaction product recycled to the first reactor unit and the remainder of the reaction product filtered to recover the cobalt.

13. An apparatus in accordance with claim 12 wherein the series of reactor units includes a first reactor unit, a final reactor and at least one intermediary reactor unit having means for agitation and aeration.

14. An apparatus in accordance with any one of claims 12 or 13 wherein each reactor unit includes a medium of microorganisms at a temperature range of 200 to 50°C at a pH of 1.2 to

15. An apparatus in accordance with any one of claims |E 12 to 14 wherein the microorganisms are a mixture of T. Ferrooxidans and L. Ferrooxidans.

16. An apparatus in accordance with claim 15 wherein the mixture is T. Ferrooxidans, L. Ferrooxidans and T. Thiooxidans.

17. An apparatus in accordance with claim 16 wherein the mixture is T. Ferrooxidans, L. Ferrooxidans, T. Thiooxidans and mixed heterotrophic organisms.

18. A method of extracting cobalt by continuous microbial leaching of cobalt-containing pyritic concentrate comprising the steps of: feeding a cobalt-containing pyritic concentrate feedstock into at least a first reactor unit, (ii) agitating and aerating the feedstock in the presence of microorganisms at a pH in the range of 1.2 to 2.5 and at a temperature in the range of r^ TP 29 to 500C to produce a reaction product slurry, (iii) neutralizing the slurry to precipitate one or more impurities in a preferred form, (iv) removing the precipitate by filtration, oxidising further impurities to insoluble precipitates utilising an oxidant, (vi) filtering the residual precipitate leaving a product liquor containing cobalt free of contaminants, (vii) recovering cobalt from the liquor.

19. A method of extracting cobalt by continuous microbial leaching of cobalt-containing pyritic concentrate comprising the steps of: feeding a cobalt-containing pyritic concentrate feedstock into at least a first reactor unit, (ii) agitating and aerating the feedstock in the i° presence of microorganisms at a pH in the range of 1.2 to 2.5 and at a temperature in the range of ~to 500C to produce a reaction product slurry 20 containing cobalt, iron and arsenic, (iii) neutralising the slurry to precipitate ferric iron as ferric hydroxide and arsenic as ferric arsenate, (iv) removing ferric hydroxide and ferric arsenate by filtration, using Unreacted pyrite and gangue 25 present in the slurry to improve the filtration of a fine ferric hydroxide, S oxidising any residual ferrous oxide to ferric iron with an oxidant, 30 (vi) filtering the residual ferric hydroxide leaving a product liquor free of iron and arsenic, (vii) recovering cobalt from the product liquor. A method in accordance with claim 19 wherein at step (iii) the pH is 2.5 6 and the temperature 25

21. A method in accordance with claim 19 or 20 wherein the pH is 2.8 to 3.

22. A method in accordance with any one of claims 18 to 21 wherein limestone or lime is used to neutralize the slurry.

23. A method in accordance with claim 19 wherein copper is recovered in step (vii).

24. A method in accordance with claim 19 wherein copper is recovered prior to step (v) A method in accordance with any one of claims 19 to 24 wherein hydrogen peroxide (H 2 0 2 sulphur dioxide (SO 2 or air are applied as oxidants to remove ferrous iron in stage (v)

26. A method in accordance with any one of claims 18 to i 24 wherein the pH at stage is 2.5 to 6 at a iK temperature of 25 to i 27. A method in accordance with claim 25, wherein if aeration is used the pH is 4.5 to 5.5 and the temperature 400C or higher.

28. A method in accordance with claim i, substantially in accordance with the Examples.

29. A method in accordance with claim 12 substantially 31 in accordance with the Examples. A method in accordance with claim 18 substantially in accordance with the Examples.

31. A method in accordance with claim 19 substantially in accordance with the Examples. DATED this 17th Day of January 1994 MOUNT ISA MINES LIMITED Attorney: IAN T. ERNST Fellow Institute of Patent Attorneys of Australia of SHELSTON WATERS t nuui U. Lecovery scnemes have been developed to I I -9' 4 VP '3 ABSTRACT A method of extracting cobalt by continuous microbial leaching of cobalt-containing pyritic concentrate comprising the steps of feeding a cobalt-containing pyritic concentrate feedstock into at least a first reactor unit, agitating and aerating the feedstock in the presence of microorganisms at a pH in the range of 1.2 to 2.5 and at a temperature in the range of 20 to 50 0 C to produce a reaction product and filtering the reaction product. 4d~d,