AU736975B2 - Oxidation of metal sulfides using thermotolerant bacteria - Google Patents

Description

1riuu/Ui 1 28SI9 Regulation 3.2(2)

AUSTRALIA

Patents Act 1990 i r's

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Application Number: Lodged: Invention Title: OXIDATION OF METAL SULFIDES USING THERMOTOLERANT

BACTERIA

The following statement is a full description of this invention, including the best method of performing it known to us .EIP AUSTRALIjA

RECEIVED

2 4DEC 1998

MELBOURNE

OXIDATION OF METAL SULFIDES USING THERMOTOLERANT

BACTERIA

Field of the Invention The present invention relates to a process for the treatment of metal containing materials by bacterial oxidation.

Background Art It is known that recovery of metals especially precious metals and base metals from refractory sulphide materials can be enhanced by bacterial oxidation or leaching. The bacterial treatment subjects the sulphide material to a pre-oxidation.

The refractory sulphide materials can take a wide variety of forms including mineral sulphides, carbonaceous sulphide ores, sulphide flotation concentrates, sulphide gravity concentrates, sulphide tailings, sulphide mattes and sulphidic fume.

The precious metals and some base metals remain in the oxidised solid residue and can be recovered by conventional carbon in pulp or other chemical leaching processes. Some base metals such as copper, zinc and nickel go into solution and may be recovered directly by conventional solvent extraction and electrowinning.

In the past, bacterial oxidation of precious or base metal containing sulphide materials has typically been conducted using bacteria of the Thiobacillus species.

0 However, the Thiobacillus species can only operate at temperatures up to about 400C. Further, the oxidation effected by Thiobacillus bacteria is an exothermic reaction and it is sometimes necessary to cool the process reactors to prevent the temperature exceeding that at which the Thiobacillus bacteria can operate.

US 4729788 discloses the use of facultative or obligate thermophiles at temperatures in excess of about 450C and ranging up to about 900C for recovery of precious metals from refractory sulphidic material and refractory carbonaceous sulphidic material not including non-ferrous base metals. The Sulpholobus bacteria exemplified are viable at temperatures of 450C and above. Optimum growth temperature would be expected in the range 600C to 900C.

Australian Patent No. 592161 discloses leaching of gold from an arsenopyritic material in a temperature range of about 300C to about 350C.

Optimum growth temperature is not disclosed but would be expected to fall in this range, the classical range for bacterial leaching.

Australian Patent No. 583151 involves leaching of an ore containing 1i reducible manganese and a precious metal; and leaching of a precious metal containing metal suiphide ore. The leach temperature adopted is in the range about 200C to about 300C. Leaching is specifically exemplified at 220C. Optimum growth temperature is not disclosed but would be expected to fall in the range about 200C to about 300C.

US 3305353 discloses leaching of sulphuritic ores by Thiobacillus ferrooxidans in the range about 200C to about 450C. Leaching is most rapid at 350C suggesting a similar optimum growth temperature. This process may likewise be described as a "classical" leaching process.

Barrett et al have described leaching of gold from an arsenopyrite ore with an arsenic adapted moderately thermophilic mixed culture. Leaching of valuable non-ferrous base metals, present in substantial proportion within the ore, is not disclosed. In Barrett et al, "The Isolation and Characterisation of a Moderately Thermophilic Mixed Culture of Autotrophic Bacteria: Application to the Oxidation of Refractory Gold Concentrates". Proceedings of Randol Perth International Gold Conference 1988, no leaching of non-ferrous base metals is disclosed.

Nobar et al, "Isolation and Characterisation of a Mixed Microbial Community from an Australian Mine. Application to the Leaching of Gold from Refractory Ores".

Biohydrometallurgy: Proceedings of the International Symposium Warwick 1987, o 0. 530-531, describe leaching of gold from refractory ores after bacterial treatment for destruction of the sulphide lattice, comprising pyrite or pyrrhotite.

Summary of the Invention l: The present invention provides a process for the bacterial oxidation of metal containing sulphide materials using thermotolerant bacteria which can operate at higher temperatures than conventional Thiobacillus bacteria.

In accordance with one aspect of the present invention, there is provided a process for recovering metals from particulate sulphide materials containing a nonferrous base metal selected from the group consisting of copper, zinc, nickel and cobalt which includes contacting the sulphide material with an aqueous solution containing a thermotolerant bacteria culture having an optimum growth temperature of 400C to 450C capable of promoting oxidation of the sulphide S material at a temperature in the range from 25 to 550C, separating the oxidised residue from the aqueous liquid; and treating the oxidised residue and/or the aqueous liquid to recover the metal therefrom.

3 The process may most advantageously be conducted in an aerated reactor as described in the Applicant's co-pending Australian Provisional Patent Application No. PP6966, filed 6th November, 1998; and Provisional Patent Application NO. PP7180, filed 18th November, 1998, the contents of which are hereby incorporated herein by reference. The process may, however, be conducted in any reactors or tanks.

The thermotolerant bacterial culture may be isolated by conventional techniques, the preferred culture being isolated from sludge and liquor samples isolated from the sole coal mine in Western Australia, at Collie and being designated "MTC-1". Such thermotolerant bacteria have characteristics as described in "Thermophiles General, Molecular, and Applied Microbiology" edited by Thomas D. Brock and published by John Wiley and Sons (1986). In Chapter 1 of this publication, there is illustrated in Figure 1 a graph showing that thermotolerant bacteria grow at temperatures lower than those preferred by moderate and obligate or extreme thermophiles.

In the context of the present invention, a thermotolerant bacterium is one which has an optimum growth temperature of 40 to 450C and an operating or leaching temperature range of 25 to 55 0

C.

Preferably, the aqueous solution used in the process of the present invention S is acidic. It has been found that the optimum acidity of the aqueous liquid for growth of the thermotolerant bacteria culture used in the present invention is in the range from pH 1.3 to 2.0, whilst the optimum acidity of the aqueous liquid for the present invention is in the range from pH 0.5 to The bacterial oxidation step of the process of the present invention is conducted in the presence of nutrients which are typically dissolved salts of ::nitrogen, potassium and phosphorus. The nutrients may already be present in the aqueous liquid or they may be added thereto. The nutrient materials promote the growth of the thermotolerant bacteria.

It is preferred that the thermotolerant bacteria be acidophilic in view of the pH conditions under which the process of the present invention is preferably conducted. Further, the thermotolerant bacteria used in the process of the present *invention are typically aerobic and thus the aqueous liquid is preferably aerated during the operation of the process to ensure that there is an adequate supply of oxygen for the bacteria. Still further, the thermotolerant bacteria culture used in the process of the present invention is typically capable of autotrophic growth. Yet further, the thermotolerant bacteria culture typically does not require additional CO2 over and above that normally available from ambient air.

The thermotolerant bacteria culture used in the process of the present invention may be capable of oxidising arsenic (III) to arsenic in acidic aqueous solutions containing soluble iron salts. Further, the thermotolerant bacteria culture used in the process of the present invention may be capable of oxidising iron (II) to iron (III) in acidic aqueous solutions and may be capable of oxidising reduced sulphur species to sulphate ion in acidic aqueous solutions.

Also, the thermotolerant bacteria culture used in the process of the present invention is preferably capable of oxidising iron and sulphides in an aqueous liquid containing up to 20 grams/litre of sodium chloride, an unexpectedly high sodium chloride concentration, without the addition of special nutrients or employment of any special conditions. Thus, provided that the pH, temperature, oxygen, nitrogen phosphate and potassium levels are maintained as discussed above, oxidation will proceed.

A particular culture of thermotolerant bacteria, such as MTC-1, may contain one or more bacteria species as evidenced by the presence of rods and spherical organisms on microscopic examination of the culture.

After completion of the oxidation step, the oxidised solid residue and the aqeuous liquid are typically separated by filtration or thickening. In the case of precious metal recovery, the oxidised solid residue would preferably be washed and then the pH of a slurry of the oxidised solid residue adjusted to a level compatible with the use of a cyanide leaching agent. Alternatively, another reagent such as thiourea could be used under acidic conditions and so the need to adjust the pH is obviated.

Examples S"The present invention will now be illustrated by reference to the following examples.

Example 1 A pyrite-gold concentrate designated P1 was treated in accordance with the present invention. The concentrate contained pyrite as the major sulphide material with minor amounts of chalcopyrite, sphalerite, galena, being sulphides of nonferrous base metals, and arsenopyrite. Other minerals present were quartz, sericite and siderite. The concentrate had the following assay.

Table 1 Assay of Pyrite Concentrate P1 Element Symbol Assay (by weight) Gold Au 52.0 ppm Iron Fe 26.0% Sulphur S 27.5% Nickel Ni 113 ppm Copper Cu 880 ppm Zinc Zn 320 ppm Lead Pb 160 ppm Arsenic As 3750 ppm Silver Ag 8 ppm Samples of the concentrate were mixed with a sulphuric acid solution at a pulp density of 3% w/w to provide a pH range of 1.2 to 1.5. Nutrients included in the acid solution were ammonium sulphate at 200 mg/L, dipotassium hydrogen phosphate at 200 mg/L and magnesium suphate heptahydrate at 400 mg/L.

The acid level (pH) may vary from the start value and may either rise and then fall; or fall from the outset. In most tests, the variation can be significant with the final pH often less than The slurry was inoculated with a thermotolerant bacteria culture designated MTC-1 in conventional manner with respect to bacterial leaching. The inoculated slurry was shaken in conical flasks at a temperature of 43°C. Samples were removed periodically and analysed for iron and arsenic extraction to determine the progress of the treatment. The sample was treated by bacterial oxidation for days to achieve 80% oxidation of the pyrite mineral. The solids weight loss due to the oxidation process was 52%. The solid residue was then separated from the residual acid solution. Leaching of the solid residue using alkaline cyanide solution recovered 92% of the gold. In comparison, cyanide leaching could recover only 74% of the gold from the concentrate in the untreated state. These results are summarised in Table 2.

Table 2 Gold Recovery from Untreated and Oxidised Concentrate Sample Iron Extracted Gold Recovered by (by weight) Cyanide Leaching (by weight) Untreated 0% 74% Bacterial Oxidation 80% 92% The cyanide solution employed to recover the gold contained sodium cyanide at a concentration of 2 g/L.

The iron in the solution from the bacterial oxidation process can be removed by adjusting the pH to above 5.0 by the addition of lime, limestone, alkaline tailings or sodium hydroxide.

The results of this test show that gold encapsulated with pyrite (FeS 2 can be released from the sulphide lattice by at least partial oxidation of the sulphur and iron by the thermotolerant bacteria culture MTC-1 to render the gold accessible to cyanide solution.

Example 2 A nickel sulphide ore designated N 1 was treated in accordance with the present invention. The ore contained both sulphidic nickel and non-sulphidic nickel minerals including violarite, lizardite and niccolite (NiAsS). Approximately of the nickel was present as sulphidic nickel. Other minerals were siderite, goethite, pyrite, chlorite and quartz. The ore had the following assay.

Table 3 Assay of Nickel Ore N1

C.

C

S

SC

5@

CS

Element Symbol Assay (by weight) Nickel Ni 2.74% Iron Fe 8.7% Samples of the ore were mixed with a sulphuric acid solution at a pulp density of 13% w/w to provide a pH range of 1.2 to 1.5. Nutrients included in the acid solution were ammonium sulphate at 200 mg/L, dipotassium hydrogen phosphate at 200 mg/L and magnesium sulphate heptahydrate at 400 mg/L.

The acid level (pH) may vary from the start value and may either rise and then fall; or fall from the outset. In most tests, the variation can be significant with the final pH often less than The slurry was inoculated with the thermotolerant bacteria culture designated MTC-1. The inoculated slurry was shaken in conical flasks at a temperature of 470C. Samples were removed periodically and analysed for iron and nickel extraction to determine the progress of the treatment.

At the completion of the bacterial oxidation treatment, 17 days, the solution was removed from the residual solids and the residual solids were washed with sulphuric acid solution to remove any residual nickel. The nickel recovery was 93% after the residual nickel was washed out of the solids residue.

The nickel could be recovered from the solution by raising the pH to a value of about 8.5, by the addition of lime or sodium hydroxide.

For comparison, the ore was also treated with iron (III) sulphate solution at pH 1.0 and 500C for 24 hours to extract nickel. Only 16% of the nickel was recovered in this process. These results are summarised in Table 4.

Table 4 Nickel Recovery from Ore N 1 Treatment Method Nickel in Residue Nickel Extraction (by weight) (by weight) Iron III Leaching 2.03% 16% Bacterial Oxidation 0.60% 78% Bacterial Oxidation and Washing 0.19% 93% The results of this test showed that base metals in ore as sulphide minerals can be recovered by the action of the thermotolerant bacteria culture MTC-1. The sulphidic minerals were oxidised to release the nickel into the acidic solution for conventional recovery.

Example 3 A gold bearing arsenopyrite pyrite concentrate was treated in accordance with the present invention. This concentrate was designated AP 1. The major sulphide minerals were pyrite, 30% by weight and arsenopyrite, 35% by weight.

Other minerals present were calcite, quartz and chlorite. The gold was present almost completely in the arsenopyrite. The concentrate had the following assay.

Table Assay of Arsenopyrite Concentrate AP 1 Element Symbol Assay (by weight) Gold Au 80 ppm Arsenic As 16.7% Iron Fe 28.1% Sulphur S 30.0% Nickel Ni Samples of the concentrate were mixed with a sulphuric acid solution at pulp density of 3% w/w to provide a pH range of 1.0 to 1.3. Nutrients included in the acid solution were ammonium sulphate at 200 mg/L, dipotassium hydrogen phosphate at 400 mg/L and magnesium sulphate heptahydrate at 400 mg/L.

The acid level (pH) may vary from the start value and may either rise or fall; or fall from the outset. In most tests, the variation can be significant with the final pH often less than The slurry was inoculated with the thermotolerant bacteria culture designated MTC-1. The inoculate slurry was shaken in conical flasks at a S temperature of 400C. Samples were removed periodically and analysed for iron and arsenic extraction to determine the progress of the treatment. The sample was treated by bacterial oxidation for 12 days to achieve 90% dissolution of the arsenopyrite mineral. The solids weight loss due to the oxidation process was 30%. The residual solids were then separated from the acid solution. Leaching of the separated solid residue using alkaline cyanide solution recovered 95% of the gold. In comparison, cyanide leaching could recover only 21% of the gold from the concentrate in the untreated state. These results are summarised in Table 6.

Table 6 Gold Recovery from Untreated and Oxidised Concentrate Sample Arsenic Extracted Gold Recovered by (by weight) Cyanide Leaching (by weight) Untreated 0% 21% Bacterial Oxidation 90% The cyanide solution employed to recover the gold contained sodium cyanide at a concentration of 2 g/L.

The arsenic and iron in the solution from the bacterial oxidation process can be removed by adjusting the pH to above 5.0 by the addition of lime, limestone, alkaline tailings or sodium hydroxide.

The results of this test show that gold encapsulated with arsenopyrite (FeAsS) can be released from the sulphide lattice by at least partial oxidation of the arsenic, sulphur and iron by the thermotolerant bacteria culture MTC-1 to render the gold accessible to cyanide solution.

Example 4 A gold bearing arsenopyrite-pyrite concentrate was treated according to the present invention. This concentrate was designated AP 2. The major sulphide minerals were pyrite, 90% by weight and arsenopyrite 9% by weight. Other minerals present were calcite, quartz and chlorite. The gold was distributed in both the arsenopyrite and the pyrite. The concentrate had the following assay.

Table 7 Assay of Arsenopyrite Pyrite Concentrate AP 2 Element Symbol Assay (by weight) Gold Au 54 ppm Arsenic As 4.2% Iron Fe 35.7% Sulphur S 40.0% S Samples of the concentrate were mixed with a sulphuric acid solution at a pulp density of 10% w/w to provide a pH range of 1.0 to 1.3. Nutrients included in the acid solution were ammonium sulphate at 200 mg/L, dipotassium hydrogen phosphate at 400 mg/L and magnesium sulphate heptahydrate at 400 mg/L.

The acid level (pH) may vary from the start value and may either rise and then fall; or fall from the outset. In most tests, the variation can be significant with the final pH often less than The slurry was inoculated with the thermotolerant bacteria culture designated MTC-1. The inoculated slurry was shaken in conical flasks at a temperature of 530C. Samples were removed periodically and analysed for iron and arsenic extraction to determine the progress of the treatment. The sample was treated by bacterial oxidation for 12 days to achieve 90% oxidation of the arsenopyrite mineral and an additional 21 days for 70% pyrite oxidation as well as arsenopyrite oxidation. The weight loss due to the oxidation process was 25% for the arsenopyrite and 78% for the 100% arsenopyrite plus 70% pyrite. The solids residue was then separated from the acid solution.

Leaching of the solid residue using alkaline cyanide solution recovered 79% of gold for the oxidation of 90% arsenopyrite and 87% for complete oxidation of the arsenopyrite and 70% of the pyrite. In comparison, cyanide leaching could recover only 53% of the gold from the concentrate in the untreated state. These results are summarised in Table 8.

Table 8 tt 0l Gold Recovery from Untreated and Oxidised Concentrate Sample Arsenic Iron Gold Extracted Extracted Recovered (by weight) (by weight) (by weight) Untreated 0% 0% 53% Bacterial 90% 25% 79% Oxidation Bacterial 100% 70% 87% Oxidation The cyanide solution employed to recover the gold contained sodium cyanide at a concentration of 2 g/L.

S The arsenic and iron in the solution from the bacterial oxidation process can be removed by adjusting the pH to above 5.0 by the addition of lime, limestone, alkaline tailings or sodium hydroxide.

The results of this test show that gold encapsulated with arsenopyrite (FeAsS) and in pyrite (FeS 2 can be released from the sulphide lattice by at least partial oxidation of the arsenic, sulphur and iron by the thermotolerant bacteria culture MTC-1 to render the gold accessible to cyanide solution. This example also shows that the MTC-1 culture is able to operate according to the invention at 530C.

The thermotolerant bacteria culture MTC-1 was isolated from the sole coal mine, that is the Collie mine, in Western Australia using well established isolation techniques developed in the late 1940s by Colmer and Hinkle. Sludge and water samples were taken and used to inoculate volumes of a modified 9K medium containing yeast extract. The samples were incubated at 300C, growth was observed after 7 days. These samples were then sub-cultured in modified 9K medium without yeast extract.

Procedure for Examples 5 to 8 In this example, a process used to test the thermotolerant bacteria was applied according to the following procedure.

Approximately one hundred and fifty grams of the mineral sulphide concentrate or ore was placed in a container with a capacity of a minimum of one and a half litres. Water was added to the container until the volume reached approximately half the required volume. A means of stirring the mixture of solids and the water was employed and the slurry mixed. An aliquot of 10ml of inoculum containing thermotolerant bacteria was added to the container and the remaining water added. The acidity of the slurry was adjusted using sulphuric acid such that the final pH was in the range 1.0 to 2.0, but usually between 1.2 and 1.6 a nutrient mixture containing ammonium sulphate, magnesium sulphate, and potassium orthophosphate was added at a level of 4, 8 and 2 grams of nutrient per kilogram of S solids. The slurry containing all the materials was placed in a hot room such that a temperature of the slurry remained at 43-440C. A pipe was then placed into the container such that air could be added to the container at a controlled rate. This was normally set at 1 litre per minute per litre of slurry to ensure that excess air was available for the process to proceed. Samples of the slurry were taken daily and the solution separated from the solids using physical methods. A sample of the solution was then analysed to determine the amount of the metals of interest that had been dissolved into the solution. The remaining slurry and solids were returned to the container. The process was allowed to continue for the time necessary for the maximum amount of the metals to be dissolved. At the end of the test, the complete contents of the container were removed and the solution separated from the solids using filtration. The solution and solids were both analysed for their metal contents and the percentage extraction determined.

Where the quantity of material varied, the amount of solids and solution was adjusted accordingly to maintain the same or similar solids densities. In some tests the concentrate was ground to a specific size before processing.

Example Three different copper concentrates were treated in accordance with the process described. The concentrates were designated C1, C2, and C3 and each contained various copper minerals.

Concentrate C1 The copper in this concentrate was contained solely in the mineral chalcopyrite (CuFeS 2 The iron sulphide mineral, pyrite, was also present as well as non-sulphide minerals, such as silicates.

Concentrate C2 The concentrate comprised a mixture of copper containing sulphide minerals being chalcopyrite, chalcocite, bornite, as well as native copper and the iron sulphide pyrite.

Concentrate C3 The concentrate contained the following copper containing sulphide minerals being chalcopyrite, covellite, chalcocite, tennantite, digenite, enargite, bornite; and cubanite. The iron sulphide, pyrite, was also present.

All three concentrates contained gold that was in recoverable quantities.

Oxidising the concentrate using the thermotolerant bacteria allowed for improved °extraction of the gold from the residue after the extraction of the copper.

Table 9 Copper and Gold Recovery from Concentrates Cl to C3 Conditions C1 C2 C3 Copper Content Head Assay 25.3 27.9 14.9 Copper Extraction Acid Leach Only 17 N/A Copper Extraction Bacterial Oxidation Leach using 97 93 81 thermotolerant bacteria Gold Content Head Assay 6 71 24 Gold Extraction No bacterial oxidation of the 10 84 N/A concentrate Gold Extraction Bacterial Oxidation Leach using 90 99 83 thermotolerant bacteria Silver Extraction Bacterial oxidation Leach using 81 N/A N/A thermotolerant bacteria Effect of Particle Size In this series of tests, particle size was controlled in various size ranges.

Table Effect of Particle Size on Copper Recovery from Concentrates CI to C3 Size (pm) 80% Conditions C1 C2 C3 passing Cu Extraction 50-60 Bacterial Oxidation Leach using 67 53 thermotolerant bacteria Bacterial Oxidation Leach using 82 83 N/A thermotolerant bacteria Bacterial Oxidation Leach using 97 93 81 thermotolerant bacteria a a a a.

Effect of Pulp Density In this series of tests, additional concentrate was added to increase the pulp density. All the material was pre-ground to Table 11 Effect of Pulp Density on Copper Recovery from Concentrate Cl1 Pulp Density Solids Conditions C 1 Cu Extraction Bacterial Oxidation Leach 98 using thermotolerant bacteria Bacterial Oxidation Leach 97 using thermotolerant bacteria Three additional copper concentrates, C4 to C6, were tested. These had lower amounts of copper but also contained the metal cobalt.

Table 12 Copper and Cobalt Recovery from Concentrates C4 to C6 Conditions C4 C5 C6 Copper Content 1.0 13.0 5.8 Cobalt Content Head Assay 0.66 0.21 0.25 Copper Extraction Bacterial Oxidation Leach using 80 93 68 Cobalt Extraction thermotolerant bacteria 61 95 79 Two concentrates C7. and C8. that nredominantlv contained thA metal C.nhnlt

S..

SSSS

were also tested in accordance with the process.

Table 13 Copper and Cobalt Recovery from Concentrates C7 and C8 Conditions C7 C8 Copper Content 0.43 0.12 Cobalt Content Head Assay 0.84 0.48 Copper Extraction Bacterial Oxidation Leach using N/A N/A Cobalt Extraction% thermotolerant bacteria 79 94 Example 6 Zinc Concentrates Two zinc concentrates, Z1 and Z2, containing the zinc mineral sphalerite were tested according to the process.

Table 14 Zinc Recovery from Concentrates Z1 and Z2 Conditions Z1 Z2 Zinc Content Head Assay 62.0 14.0 Zinc Extraftion Bacterial Oxidation Leach using 90 88 thermotolerant bacteria xample 7 a a a a.* a a a *o *o oo* *oooo* o* o o Polymetallics Concentrates A polymetallic concentrate, M1, containing a mixture of mineral sulphides was treated to extract nickel, copper and cobalt. The concentrate contained the nickel mineral pentlandite, as well as nickel contained within the structure of the mineral pyrrhotite, the main copper mineral was chalcopyrite. The metal cobalt was associated with the nickel minerals.

Table Copper, Nickel and Cobalt Recovery from Concentrate M1 Conditions M1 Copper Content Head Assay Nickel Content 3.6 Cobalt Content 0.27 Copper Extraction Acid Leach only 12 Nickel Extraction Cobalt Extraction 13 Copper Extraction Bacterial Oxidation Leach using thermotolerant 82 Nickel Extraction bacteria 99 Cobalt Extraction 98 Effect of Particle Size Table 16 Effect of Particle Size on Copper, Nickel and Cobalt Extraction from Concentrate M1 Conditions Size (gmr) M1 Head Assay 80% passing Copper Extraction Bacterial Oxidation Leach using 50-60 44 Nickel Extraction thermotolerant bacteria 56 Cobalt Extraction 57 Copper Extraction Bacterial Oxidation Leach using 10 82 Nickel Extraction thermotolerant bacteria 99 Cobalt Extraction 98

S

S. S S SS 5 Aampl o Polymetallic Concentrate A concentrate, M2, containing a mixture of mineral sulphides was treated to extract copper, zinc and cobalt. The concentrate contained the copper containing sulphide minerals covellite, chalcopyrite (CuFeS 2 and bornite; the zinc sulphide sphalerite; and the nickel mineral pentlandite, as well as nickel contained within the structure of the mineral pyrrhotite. The metal cobalt was associated with the nickel minerals.

Table 17 Cobalt, Zinc. Cobalt and Nickel Recovery from Concentrate M2 Conditions M2 Copper Content Head Assay Zinc Content Cobalt Content 1.1 Nickel Content 0.8 Copper Extraction Bacterial Oxidation Leach using thermotolerant Zinc Extraction bacteria 99 Cobalt Extraction Nickel Extraction 93 All four metals were recovered from bacterial oxidation solution using solvent extraction. Modification of the pH was necessary to achieve the separation of the metals.

Table 18 Copper, Zinc. Cobalt and Nickel Recovery from Concentrate M2 by Solvent Extraction Conditions Solvent pH M 2 Extraction Extraction Reagents Copper Extraction Solvent LIX 984N 2.0 99 Zinc Extraction Extraction Cyanex 272 2.8 94 Cobalt Extraction Cyanex 272 5.0 98 Nickel Extraction Versatic Acid 6.2 93 17a Example 9 Zinc Tailings Two samples of zinc flotation tailings Z3 and Z4 containing the zinc material sphalerite were leached according to the procedure above described for Examples to 8. No prior leaching had been undertaken. The iron sulphide pyrite was also present.

Table 19 Zinc Recovery from Flotation Tailings 23 and 24 Conditions Z3 Z4 Zinc Content 0.84 0.62 Zinc Extraction Bacterial Oxidation Leach using 100 89 moderately thermophilic bacteria Modifications and variations may be apparent to the skilled reader or review of this disclosure. Such modifications and variations fall within the scope of the present invention.

9* 9* 9999 9 9 9* 9 *9 *99.

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Claims (6)

1. A process for recovering metals from particulate sulphide materials containing a non-ferrous base metal selected from the group consisting of copper, zinc, nickel and cobalt which includes contacting the sulphide material with an aqueous solution containing a thermotolerant bacteria culture having an optimum growth temperature of 400°C to 450°C capable of promoting oxidation of the sulphide material at a temperature in the range from 25 to 55°C, separating the oxidised residue from the aqueous liquid; and treating the oxidised residue and/or the aqueous liquid to recover the metal therefrom.

2. The process of claim 1 wherein said particulate sulphide material is selected from the group consisting of pentlandite, sphalerite, chalcopyrite, chalcocite, bornite, digenite, enargite, cubanite, covellite, tennantite, violarite, millerite or an ore containing one or more of the materials.

3. The process of claim 1 or claim 2 wherein said recovered metal is copper.

4. The process of any one of the preceding claims wherein said recovered metal is zinc. *l o S The process of any one of the preceding claims wherein said recovered metal is nickel.

6. The process of any one of the preceding claims wherein said recovered metal is cobalt. S S7. The process of any one of the preceding claims wherein final pH is less than 1 *.So

8. The process of any one of the preceding claims wherein said thermotolerant bacteria culture is designated MTC-1. 9 The process substantially as herein before described with reference to Examples 1 to 9. DATED this 29th day of December, 1998. BACTECH (AUSTRALIA) PTY. LTD. WATERMARK PATENT TRADEMARK ATTORNEYS 4TH FLOOR "DU RACK CENTRE" 263 ADELAIDE TERRACE PERTH WA 6000 VAX DOC 023. AU002864.WPC RHB:JN