METAL RECOVERY

RECUPERATION DE METAL

English Abstract

A method of extracting metal from sulphide ores, which includes the steps
of solubilizing the metal into a sulphate solution, and generating sulphide
by anaerobic bacterial action in the sulphate solution, thereby to cause
the metal in the solution to be precipitated as an insoluble sulphide, thus
upgrading the metal into a highly concentrated form.

Claims

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CLAIMS
1. A method of extracting metal from sulphide ores, which includes the
steps of solubulizing the metal into a sulphate solution which is generated
by means of an acid dissolution process, and generating sulphide by
anaerobic bacterial action in the sulphate solution, thereby to cause the
metal in the solution to be precipitated as an insoluble sulphide, thus
upgrading the metal into a highly concentrated form.
2. A method according to claim 1 wherein the sulphate solution is
passed through a bed of inert material to which bacteria become attached
and use is made of the bacterium Desulfovivrio Desulfuricans to effect
sulphide generation.
3. A method according to claim 1 wherein the ore is crushed and
treated by heap leaching with iron sulphate solutions which carry at least
one of the following bacteria: Thiobacillus ferrooxidans, Thiobacillus
thiooxidans, and Leptospirillum ferrooxidans.
4. A method according to claim 1 wherein the metal sulphates are
solubilized directly by at least one of the following bacteria: Thiobacillus
ferrooxidans, Thiobacillus thiooxidans, and Leptospirillum ferrooxidans.

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5. A method according to claim 1 wherein finely milled ore is treated
by froth flotation to form a metal sulphide flotation concentrate which is
treated in one or more tanks using at least one of the following bacteria:
Thiobacillus ferrooxidans, Thiobacillus thiooxidans, and Leptospirillum
ferrooxidans.
6. A method according to claim 1 in which the pH of the sulphate
solution is maintained within the range of from 1,2 to 3,0 during the step of
solubilizing the metal.
7. A method according to claim 6 wherein the pH is maintained within
the range of from 2,0 to 2,5 during the step of solubilizing the metal.
8. A method according to claim 1 wherein the precipitated metal
sulphide is separated from the solution and processed to recover the
metal.
9. A method according to claim 1 wherein the acid is generated by
bacterial leaching of the ore.

Description

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BACKGROUND OF THE INVENTION
This invention relates to the recovery of metal such as nickel, copper,
cobalt or the like, from sulphide ores.
SUMMARY OF THE INV~NTIION
According to the invention there is provided a method of extracting metal from
sulphide ores, which includes the steps of solubulizing the metal into a
sulphate solution which is generated by means of an acid dissolution process,
and generating sulphide by anaerobic bacterial action in the sulphate
solution,
thereby to cause the metal in the solution to be precipitated as an insoluble
sulphide, thus upgrading the metal into a highly concentrated form.
The sulphide is generated in a reactor. The sulphate solution may be
passed through a bed of inert material to which bacteria become attached
and use may be made of the bacterium Desulfovivrio Desulfuricans to
effect sulphide generation.
Nutrients may be used to enhance sulphide generation and inert gas such
as nitrogen may be used for maintaining the anaerobic environment.

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The method includes the step of generating the sulphate solution for example
by means of an aad dissalution process.
Acid may be generated by treating the ore by bacterial action.
In one embodiment of the invention the ore is crushed and treated by
heap leaching with iron sulphate solutions which, optionally, carry
bacteria. The bacteria may be Thiobacitlus ferrooxidans, Thiobacillus
thiooxidans, or Leptospiriilum ferrooxidans. Sulphuric acid is then
generated and the sulphate solution is formed.
Alternatively the metal sulphates are solubilized directly by bacterial action
using one or more of the aforementioned bacteria.
Sulphuric acid or an alkali such as lime may be added to the solution to
maintain the pH within the range of 1,2 to 3,0, and preferably within the
range of 2,0 to 2,5.
The metal sulphate solution may alternatively be generated by treating a
froth flotation concentrate. In this case a finely milled ore may be treated
by froth flotation to form a metal sulphide flotation concentrate. The
concentrate may then be treated to form the sulphate solution. This may,
for example, take place in a series of tanks with a solution containing one

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or more of the aforementioned bacteria.
The metal sulphide which is precipitated may be separated from the
solution by any physical separation method, for example filtration or the
like. The precipitation step may take place in the vessel in which the
sulphide is generated, or in a separate vessel. Thereafter the precipitate
can be processed in any suitable way, e.g. smelting, roasting or the like,
to recover the metal.
BRIEF DESCRIPTION OF THE DRAWING
The invention is further described by way of example with reference to the
accompanying flow sheet which illustratEa two methods of extracting
metal from sulphide ores according to they invention.
DESCRIPTION OF PREFERRED EMSODINBENTS
The process of the invention is applicable to the extraction of metal, in
particular nickel, copper and cobalt, contained in sulphide ores. The
following description is however made with reference to a nickel recovery
process only. It is to be understood though that the following principles

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can be applied equally to the recovery of copper and cobalt.
Referring to the flow sheet the mined ore is crushed at a stage 10 and the
crushed ore is piled on a prepared base and treated in a leaching process
12. In the leaching process 12, iron sulphate solutions carrying
Thiobacilius ferrooxidans, Thiobacillus thiooxidans, or l_eptospirillum
ferrooxidans, or a mixture of any two or all three of the bacteria, are
percolated through the heap. in this way nickel sulphate, iron sulphate
and sulphuric acid are generated.
According to the alkalinity of the ore further sulphuric acid or lime may be
added to maintain the pH within the preferred range of 1,6 to 2,5 in which
the viability of the bacteria is ensured.
The solution then passes to a biological sulphide reduction process 14
where, under anaerobic conditions and in a suitable reactor or in a series
of reactors, soluble sulphates are converted to sulphide. In the presence
of the soluble sulphide the nickel Is precipitated as an insoluble nickel
sulphide. Precipitation may be effected in the same reactor or reactors,
or in a separate vessel or vessels. Iron in the solution is reduced to the
ferrous state and does not precipitate with the nickel sulphide. This step
is more fully described in the specification of South African patent
No. 89/7731 issued July 25, 1990.

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In a stage 16 the precipitated nickel sulphide is physically separated by
means of filtration or any other appropriate method. This may be
accomplished in the vessel in which the sulphide is generated, or in a
separate vessel.
In a subsequent step 18 the nickel sulphide is further processed in any
appropriate way, such as smelting, roasting or the like, to recover the
nickel.
Where the grade of the deposit is sufficiently high to justify additional
mechanical processing costs the ore is finely milled in a step 20 and
subjected to a froth flotation process 22 whereby a nickel sulphide
flotation concentrate is produced. As is indicated by the numeral 24 this
concentrate is subjected to biological oxidation in one or more tanks
using one or more of the bacteria Thiobacillus ferrooxidans, Thiobacillus
thiooxidans and Leptospirillum ferrooxidans, thereby to dissolve the nickel
to form the sulphate solution. The oxidation step may take place at a pH
of from 1,2 to 3,0, and preferably the pH lies in the range of 2,0 to 2,5.
The sulphate solution can then be treated as described hereinbefore.

Representative Drawing