AP379A

AP379A - Bacterial oxidation of metal containing materials.

Info

Publication number: AP379A
Application number: APAP/P/1992/000367A
Authority: AP
Inventors: Peter Andrew Spencer; Julia Rose Budden; Jack Barrett; Martin Neville Hughes; Robert Keith Poole
Original assignee: Bac Tech Industrial Pty Limited
Priority date: 1991-03-22
Filing date: 1992-03-20
Publication date: 1995-03-09
Also published as: ZA922051B; BG98117A; CA2132440A1; CA2132440C; US5429659A; BG61110B1; AP9200367A0; WO1992016667A1; ZW4692A1

Abstract

A processing

Description

DESCRIPTION in .'r.e present invent ton relates tt a nrttess :;r the cf metal containing materials cv bacterial oxidation.

RIELS GE THE INVENTION

It Is kncwr. that reccverv of metals especially precious metals ar.d case metals from refrectcrv sulphide material; car be enhanced by bacterial oxidation or leacrir.g. The bacterial treatment subjects the sulpnioo materia^ to a pre-oxidation. The refractory sulphide materials can ta.wide variety of forms including mineral sulphides, ea .ment :aroor.acecus sui:

I o r-ι r- Π s, sulphide ration concentrate .vem sulphide gravity concentrates, sulphide tailings, sulphide mattes ard 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 case metals such as copper, sine and nickel gc into solution and may be recovered directly by conventional sc' extraction and eiectrowinnir.g.

In the cast, bacterial oxidation of precious cr containing sulphide materials has typically been conducted using bacteria cf the Thiobacillus species. However, the Thiobacillus species car cnly operate it temperatures up to about 40°C. Further, the oxidation effected by Thiobacillus bacteria is ar exothermic reaction and it is sometimes necessary to cool the process reactors to prevent the

APO00379

- 3 bacteria can operate.

SUMMARY OF THE INVENTION

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 fcr recovering metals from particulate refractory precious or base metal containing sulphide materials which comprises contacting the sulphide material with an aqueous solution containing a thermotolerant bacteria culture (as herein defined) 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 metal therefrom.

DESCRIPTION OF THE INVENTION

The thermotolerant bacteria used in the present invention are as described in Thermophiles General, Molecular, and

Applied Microbiology edited by Thomas D. Brock and published by John Wiley & Sons (1986). In Chapter 1 of this l publication, there is illustrated in Figure 1(b) a graph shewing 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 bacteria is one which has an optimum growth temperature of 40 to 45°C and an operating temperature of 25 to 55’C.

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- 3a Thermotolerant bacteria are found in soil and water in certain locale. Any suitable method for isolation of the thermotolerant bacteria may be used, such as agar plating, critical end point dilution or solution growth, all of which are standard microbiology procedures.

The thermotolerant culture is preferentially acidophilic and operates most effectively in the temperature range of 40-45°C. An example of a thermotolerant acidophile is Sulfobacillus species. These bacteria are generally found in sulphide deposits and hot springs. Examples of the locale where such bacteria are found include hot springs located in Iceland and New Zealand.

Preferably, the aqueous solution used in the process of the

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- 4 present invention is acidic. It has been found that the optimum acidity of the aqueous Liquid for growth of the thermotoierant bacteria culture used in tne present invention ts ir. tne rance rrom ~r. l.j to 1.3, whilst the optimum acidity if the aqueous l^ruid for sceration of tne process of the present invention is in the range from pH

Z * z

The bacterial oxidation step tf tne process of the present invention is conducted in the presence of nutrients white arc typically cissem/cc sa_ts ~r 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 thermotoierant bacteria.

It is preferred that the thermetoierant bacteria be acidcphiiic in view of the pH conditions under which the process of the present invention is preferably conducted. Further, the thermotoierant 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 cf oxygen for the bacteria. Still further, it is found that the thermotoierant bacteria culture used in the precess cf the present invention is typically capable of autotrophic growth. Tot further, the thermotoierant bacteria culture typically does not require additional CO over and above that normally available from ambient air.

the present invention may be capable of oxidising arsenic (III) to arsenic (V) 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 tc sulphate ion in acidic aqueous solutions.

Alsc, the thermotolerant bacteria culture used in the *

precess 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 without the addition of special nutrients or employment of the special conditions. Thus, in this case extracting the pH, temperature, oxygen, nitrogen phosphate and potassium levels are maintained as discussed above, oxidation will proceed.

Typically, a particular culture of thermotolerant bacteria contains one or more bacteria species.

The process of the present invention can be operated in heaps, dumps, agitated systems or dams.

After completion of the oxidation step the oxidised solid residue and the aqueous liquid are typically separated. In the case of precious metal recovery, the oxidised solid residue would preferably be washed and then the pH of the oxidised solid residue adjusted tc 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.

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EXAMPLES

The present invention will· now ce illustrated by the following examples.

EXAMPLE 1

A pyrite - gold concentrate designated P 1 was treated in accordance with the present invention. The concentrate contained pyrite as the major sulphide mineral with minor amounts of cnalccpyrite, sphalerite, galena and arsenopvrite. Other minerals present were quartz,'sericite 10 and siderite.

The concentrate had the following assay.

Table 1

	Assay of Pyrite Concentrate ? 1
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	?b	160 ppm
Arsenic	As	3750 ppm
Silver	Ag	8 ppm
Samples of	the concentrate	were mixed	with a sulphuric
solution at	a pulp density	of 3% w/w	to provide a pH r

of 1.2 to 1.5. Nutrients included in the acid solution were ammonium-sulphate at 200 mg/L, di-potassium hydrogen phosphate at 200 mg/L and magnesium sulphate heptahydrate

X 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 1.0.

The slurry was inoculated with a thermotoierant bacteria culture designated MTC 1. 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 30 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

Untreated

Sacterial

Iron Extracted (by weight)

0%

80%

Gold Recovered

3v Cyanide

Leaching (by weight)

4%

92%

Oxidation

The cyanide solution employed to recover the gold contained sodium cyanide at a concentration of 2 g/L.

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AP Ο Ο Ο 3 7 9 '%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) 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 Ν 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 (NiAs).

Approximately 70%' 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 Ν 1

Element Symbol Assay (by weight)

Nickel Ni 2.74%

Iron Ee 18.7%

Samples of the ore were mixed with a sulphuric acid solution at a pulp density cf 13% w/w to provide a pH range of 1.2 tc

1.5. Nutrients included in the acid solution were ammonium sulphate at 200 mg/L, di-potassium hydrogen phosphate at 200 mg/L and magnesium sulphate heptahydrate at 400 mg/L.

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- 9 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 1.0.

The slurry was inoculated with the thermotolerant bacteria 5 culture designated MTC 1. The inoculated slurry was shaken ir.

conical flasks at a temperature of 47°c. Samples were removec periodically and analysed for iron and nickel extraction to determine the progress of the treatment.

At the completion of the bacterial oxidation treatment, 17 10 days, the solution was removed from the residual solids and the residual solids 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 50°C for 24 hours to extract *

nickel. Only 16% of the nickel was recovered in this process.

These results are summarized in Table 4.

Table 4

Nickel Recovery from Ore Ν 1

Treatment	Nickel in	Nickel
Method	Residue	Extraction

5 (by weight) (by weight)

Iron (III)	2.0 3 %	16%
Leaching
Bacterial	0.60%	78%

Oxidation

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- 10 Bacterial 0.19% 93%

Oxidation

S. Washing

The results of this rest showed -hat case metals in ore as sulphide minerals can be recovered 'ey the action of the thermotolerant bacteria culture MTC 1. The sulphidio minerals were oxidised to release the nickel into the acidic solution for conventional recovery.

EXAMPLE 3

A cold bearing arsenopyrite - pyrite concentrate was treated according to 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 5

Assay of Arsenopyrite Concentrate AP 1

Element

Assay (by weight

Symbol

L 0

Gold	Au	30 ppm
Arsenic	. As *	16.7%
Iron	Fe	23.1%
Sulphur	«»,	30.0%
Nickel	Ni	1. 5 %

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 1.0 to 1.3. Nutrients included in the acid solution were ammonium sulphate at 200 mg/L, di-potassium hydrogen

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2Q (

2Q 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 he significant with the final pH often less than 1.0.

The slurry was inoculated with the thermotolerant bacteria culture designated MTC 1. The inoculate slurry was shaken tn conical flasks at a temperature of 40°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 12 days tc achieve 90% break down 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

Gold Recovered

Untreated

Extracted by Cyanide ( by weight)

Leaching (by weight)

0%

3acterial Oxidation 90%

The cyanide solution employed to recover the gold contained

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- 12 sodium cyanide at a concentration of 2 g/L.

The arsenic and iron in the solution frcm 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 shew 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 created according to the present invention. This concentrate was designated AP 2. The major sulphide minerals were pyrite, 90¾ 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	5 4 ppm
Arsenic	As	4.2%
Iron	Fe	2 5.7%
Sulphur	S	40.0%
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

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- 13 were ammonium sulphate at 200 mg/L, di-potassium hydrogen phosphate at 400 mg/L and magnesium sulphate heptahydrate at 400 mg/L.

The slurry was inoculated with the thermotolerant bacteria culture designated MTC 1. The inoculated slurry was shaken .in conical flasks at a temperature of 53°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 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 3

Gold Recovery from Untreated and Oxidised Concentrate

Sample Arsenic Iron % Gold

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- 14 Recovered

Extracted weight) (hy weight)

Untreated 0%

53%

Bacterial Oxidation 90%

79%

Bacterial Oxidation 100%

Extracted (by (by weight)

0%

25%

70%

37%

The arsenic and iron in the solution from the bacterial oxidation process can be removed by adjusting the pH to '15 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 (FeS2) 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

53°C.

The thermotolerant bacteria culture MTC 1 was isolated from a coal mine in Western Australia. Sludge and water samples

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V

Basal Salts (NH₄)₂SO₄ k₂hpo₄

MgSO₄7H₂0

FeSO₄

H,S0₄ to reduce pH to 1.2

- 15 from the mine which contained acidophilic, thermotolerant bacteria were taken and used to inoculate volumes of a modified 9K medium containing yeast extract. The modified 9K medium had the following composition:Concentration

0.2 g/L 0.2 g/L 0.4 g/L to 9.000 mg/L iron

The samples were incubated at 30°C in a mineral salts solution containing 400mg/L (NH₄)₂SO₄, 200 mg/L MgSO₄ 7H₂O, lOOmg/L K₂HPO₄, lOOmg/L KC1, and pyrite 1.0 g/L at a pH of 2.0. Growth was observed after 7 days. These samples were then sub cultured in modified 9K medium without yeast extract.

Modifications and variations such as would be apparent to a skilled addressee are deemed within the scope of the present invention.

Claims

1. A process for recovering metals from particulate refractory precious or base metal containing sulphide material characterised in that it comprises contacting the sulphide material with an aqueous solution at a temperature in the range from 25 to 55°C, the

5 aqueous solution containing a thermotolerant bacteria culture having an optimum growth temperature of 40 to 45 °C and 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 metal therefrom.

/10

2. A process according to claim 1, characterised in that the aqueous solution is acidic.

3. A process according to claim 2, characterised in that the aqueous solution has a pH in the range from 0.5 to 2.5.

4. A process according to any one of claims 1 to 3, characterised in that the thermotolerant bacteria is acidophilic.

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5. A process according to any one of the preceding claims, characterised in that the thermotolerant bacteria is aerobic.

6. A process according to claim 5, characterised in that the aqueous liquid is aerated during the operation of the process.

7. A process according to any one of the preceding claims, characterised in that the

20 thermotolerant bacteria is capable of autotrophic growth.

/

8. A process according to any one of the preceding claims, characterised in that no CO, is supplied to the thermotolerant bacteria during the operation of the process other than that available from ambient air.

9. A process according to any one of the preceding claims, characterised in that the 25 aqueous liquid contains sodium chloride in an amount up to 20 grams per litre.