Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Reexamination Certificate
2002-07-19
2004-12-21
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
C075S743000, C205S580000, C266S079000, C423SDIG001
Reexamination Certificate
active
06833020
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the recovery of copper from copper bearing sulphide minerals.
Commercial bioleach plants which are currently in operation treating sulphide minerals, typically operate within the temperature range of 40° C. to 50° C. and rely on sparging air to the bioleach reactors to provide the required oxygen. Operation at this relatively low temperature and the use of air to supply oxygen, limit the rate of sulphide mineral oxidation that can be achieved. For example carrolite and enargite are relatively slow leaching at temperatures below 50° C., and treatment at or below this temperature would result in poor and sub-economic metal extraction.
The use of high temperatures between 50° C. and 100° C. greatly increases the rate of sulphide mineral leaching.
The solubility of oxygen is however limited at high temperatures and the rate of sulphide mineral leaching becomes limited. In the case of using air for the supply of oxygen, the effect of limited oxygen solubility is such that the rate of sulphide mineral leaching becomes dependent on and is limited by the rate of oxygen transfer from the gas to the liquid phase.
The bioleaching of secondary copper bearing sulphide minerals is similarly problematic and to the applicant's knowledge no commercial copper bioleach plants are in operation.
More particularly chalcopyrite has long been known to be generally refractory to bioleaching using mesophiles. A major challenge is the leaching of chalcopyrite, on an industrial scale, using thermophilic microorganisms.
SUMMARY OF THE INVENTION
The invention provides a method of recovering copper from a copper bearing sulphide mineral slurry which includes the steps of:
(a) subjecting the slurry to a bioleaching process,
(b) supplying a feed gas which contains in excess of 21% oxygen by volume, to the slurry, and
(c) recovering copper from a bioleach residue of the bioleaching process.
The method may include the step of pre-leaching the slurry prior to the bioleaching process of step (a). The pre-leaching may be effected using an acidic solution of copper and ferric sulphate.
The method may include the step of removing ferric arsenate from the bioleach residue before step (c). The ferric arsenate may be removed by precipitation.
The bioleach residue may be subjected to a neutralisation step which produces carbon dioxide which is fed to the feed gas of step (b), or directly to the slurry.
In step (c) copper may be recovered using a solvent extraction and electrowinning process. Oxygen which is generated during the copper electrowinning may be fed to the feed gas of step (b), or directly to the slurry.
Raffinate, produced by the solvent extraction, may be supplied to at least one of the following: the bioleaching process of step (a), and an external heap leach process.
Oxygen generated during the electrowinning process may be fed to the feed gas of step (b), or directly to the slurry.
The said slurry may contain at least one of the following: arsenical copper sulphides, and copper bearing sulphide minerals which are refractory to mesophile leaching.
The slurry may contain chalcopyrite concentrates.
As used herein the expression “oxygen enriched gas” is intended to include a gas, eg. air, which contains in excess of 21% oxygen by volume. This is an oxygen content greater than the oxygen content of air. The expression “pure oxygen” is intended to include a gas which contains in excess of 85% oxygen by volume.
Preferably the feed gas which is supplied to the slurry contains in excess of 85% oxygen by volume ie. is substantially pure oxygen.
The method may include the step of maintaining the dissolved oxygen concentration in the slurry within a desired range which may be determined by the operating conditions and the type of microorganisms used for leaching. The applicant has established that a lower limit for the dissolved oxygen concentration to sustain microorganism growth and mineral oxidation, is in the range of from 0.2×10
−3
kg/m
3
to 4.0×10
−3
kg/m
3
. On the other hand if the dissolved oxygen concentration is too high then microorganism growth is inhibited. The upper threshold concentration also depends on the genus and strain of microorganism used in the leaching process and typically is in the range of from 4×10
−3
kg/m
3
to 10×10
−3
kg/m
3
.
Thus, preferably, the dissolved oxygen concentration in the slurry is maintained in the range of from 0.2×10
−3
kg/m
3
to 10×10−3 kg/m
3
.
The method may include the steps of determining the dissolved oxygen concentration in the slurry and, in response thereto, of controlling at least one of the following: the oxygen content of the feed gas, the rate of supply of the feed gas to the slurry, and the rate of feed of slurry to a reactor.
The dissolved oxygen concentration in the slurry may be determined in any appropriate way, e.g. by one or more of the following: by direct measurement of the dissolved oxygen concentration in the slurry, by measurement of the oxygen content in gas above the slurry, and indirectly by measurement of the oxygen content in off-gas from the slurry, taking into account the rate of oxygen supply, whether in gas enriched or pure form, to the slurry, and other relevant factors.
The method may include the step of controlling the carbon content of the slurry. This may be achieved by one or more of the following: the addition of carbon dioxide gas to the slurry, and the addition of other carbonaceous material to the slurry.
The method may extend to the step of controlling the carbon dioxide content of the feed gas to the slurry in the range of from 0.5% to 5% by volume. A suitable figure is of the order of 1% to 1.5% by volume. The level of the carbon dioxide is chosen to maintain high rates of microorganism growth and sulphide mineral oxidation.
The bioleaching process is preferably carried out at an elevated temperature. As stated hereinbefore the bioleaching rate increases with an increase in operating temperature. Clearly the microorganisms which are used for bioleaching are determined by the operating temperature and vice versa. As the addition of oxygen enriched gas or substantially pure oxygen to the slurry has a cost factor it is desirable to operate at a temperature which increases the leaching rate by an amount which more than compensates for the increase in operating cost. Thus, preferably, the bioleaching is carried out at a temperature in excess of 40° C.
The bioleaching may be carried out at a temperature of up to 100° C. or more and preferably is carried out at a temperature which lies in a range of from 60° C. to 85° C.
In one form of the invention the method includes the step of bioleaching the slurry at a temperature of up to 45° C. using mesophile microorganisms. These microorganisms may, for example, be selected from the following genus groups:
Acidithiobacillus
(formerly
Thiobacillus
);
Leptosprillum; Ferromicrobium
; and
Acidiphilium.
In order to operate at this temperature the said microorganisms may, for example, be selected from the following species:
Acidithiobacillus caldus
(
Thiobacillus caldus
);
Acidithiobacillus thiooxidans
(
Thiobacillus thiooxidans
);
Acidithiobacillus ferrooxidans
(
Thiobacillus ferrooxidans
);
Acidithiobacillus acidophilus
(
Thiobacillus acidophilus
);
Thiobacillus prosperus; Leptospirillum ferrooxidans; Ferromicrobium acidophilus
; and
Acidiphilium cryptum.
If the bioleaching step is carried out at a temperature of from 45° C. to 60° C. then moderate thermophile microorganisms may be used. These may, for example, be selected from the following genus groups:
Acidithiobacillus
(formerly
Thiobacillus
);
Acidimicrobium; Sulfobacillus; Ferroplasma
(
Ferriplasma
); and
Alicyclobacillus.
Suitable moderate thermophile microorganisms may, for example, be selected from the following species:
Acidithiobacillus caldus
(formerly
Thiobacillus caldus
);
Acidimicrobium ferrooxidans; Sulfobacillus acidophilus; Sulfobacillus disulfidooxidans; S
Basson Petrus
Dew David William
Miller Deborah Maxine
Andrews Melvyn
Billiton Intellectual Property B.V.
Jones Tullar & Cooper P.C.
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