Base metal recovery

Details Base metal recovery Base metal recovery

1999-05-06

2001-08-28

King, Roy (Department: 1742)

Specialized metallurgical processes, compositions for use therei

Processes

Free metal or alloy reductant contains magnesium

C075S744000, C423S041000, C423S109000, C423S150100

Reexamination Certificate

active

06280501

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to extracting the base metals copper, nickel, cobalt or zinc from materials containing them.
2. Description of the Related Art
Copper sulphide concentrates are typically processed to metal by smelters. Although very efficient, smelters generate substantial quantities of sulphur dioxide gases (SO
2
) that must be captured to protect the environment. The SO
2
captured is normally converted to sulphuric acid. The capture of SO
2
and the generation of sulphuric acid significantly increase the costs of smelting copper sulphide concentrates and generates a by-product, sulphuric acid, that has a very weak market because of surplus and transportation costs.
Some gold ores or concentrates containing cyanide-soluble copper minerals cannot be treated economically because of the high operating costs due to the consumption of cyanide by copper.
Various hydro-metallurgical processes have been developed to replace smelters for treating copper sulphide concentrates. Among others, these processes include pressure leaching (either at high, medium or low temperature), ferric ion (Fe
3+
) leaching, and bacterial leaching.
The ability of ferric ion to attack metal sulphides is generally known. In the case of Chalcopyrite (CuFeS
2
), Coveilite (Cu
2
S), or Chalcocite (CuS) concentrates, the oxidation/leaching reactions with ferric can be written as:
CuFeS
2
+4Fe
3+
→Cu
2+
+5Fe
2+
+2S
0
  (1)
 Cu
2
S+4Fe
3+
→2Cu
2+
+4Fe
2+
+S
0
  (2)
CuS+2Fe
3+
→Cu
2+
+2Fe
2+
+2S
0
  (3)
The ferric can be added either as ferric chloride or ferric sulphate, although it is known that ferric chloride is kinctically favored over ferric sulphate.
Reactions (1) and (2) indicate that, for example, to dissolve 20 g/L Cu in solution, the leach solution needs at least 70 g/L Fe
3+
and 17.4 g/L Fe
3+
for Chalcopyrite and Covellite concentrates respectively. Though useful as a replacement for smelters, ferric ion reaction processes are undesirable, in some cases, because they generate leach solutions containing high levels of dissolved salts and are difficult to process further. Chalcopyrite is known to be a copper mineral which is refractory to chemical dissolution in typical leach conditions, and the reaction (1) indicates that it requires a relatively high dosage of ferric to be dissolved in acid solutions.
One alternative is to regenerate the ferric during the leaching process, that is by oxidizing the ferrous ion to its ferric state. Conventionally either chlorine gas or pure oxygen are used as oxidants in this case, the former in the following reaction:
FeCl
2
+½Cl
2
→FeCl
3
  (4)
However, chlorine gas is expensive and relatively dangerous to handle and the reaction using pure oxygen gas is too slow to be a feasible oxidant.
Copper heap leaching has become the method of choice, particularly for treating low grade oxidized copper ores, The method is only partially successful in treating copper ores containing secondary copper minerals such as Chalcocite and Covellite, unless the dissolution of these copper minerals is bacterially assisted by organisms such as
Thiobacillus Ferroxidans
and
Thiobacillus Thiooxidans
. The practical application of these bacteria strains is delicate because they require a precise range of temperatures and acidity as well as a range of specific nutrients in order to function properly.
It is an object of the present invention to obviate or mitigate the above mentioned problems.
It is another aspect of the present invention to provide a novel technique for extracting a base metal from a material.
It is still another object of the present invention to provide a novel technique for extracting a base metal from a sulphide material.
It is still another object of the present invention to provide a process by which copper sulphide concentrate can be efficiently leached by ferric sulphate solutions using lower overall ferric ion concentrations than in prior art processes.
SUMMARY OF THE INVENTION
In one of its aspects, the present invention provides a process for recovering a base metal from a material, the base metal being selected from cobalt, copper, nickel and zinc, the process comprising the steps of:
reacting the material with a ferric ion species in a leach solution, at conditions sufficient to cause at least a portion of the base metal to be oxidized by the ferric ion species, thereby causing the ferric ion species to be converted to a ferrous ion species, and
oxidizing the ferrous ion species with an oxidation mixture of SO
2
and oxygen to form the ferric ion species for subsequent reaction with the material.
In another aspect of the present invention, there is provided a process of treating a material containing a base metal selected from cobalt, copper, nickel and zinc, comprising the steps of:
a) exposing the material to a leach solution including a first ferric ion species therein, at conditions sufficient to liberate at least a portion of the base metal, thereby causing the first ferric ion species to be reduced to a first ferrous ion species,
b) reacting the first ferrous ion species with an oxidation mixture of SO
2
and oxygen, at conditions sufficient to oxidize the first ferrous ion species to a second ferric ion species;
c) exposing the material to the leach solution including the second ferric ion species at conditions sufficient to liberate a base metal ion, thereby causing the second ferric ion species to be reduced to a second ferrous ion species, and
d) repeating step b) for the second ferrous ion species,
In another embodiment, the base metal-bearing material is in a heap and wherein steps (a) and (c) include the step of directing the oxidation mixture through the heap. The step of directing may include the step of blowing the sure through pipes located in, or at the bottom of, the heap, although the oxidation mixture may also be directed, as an aqueous mixture, through the heap by percolating the mixture there through, for example.
In another embodiment, the mixture is aqueous and steps (a) and (c) include the step of establishing SO
2
in the mixture by sparging SO
2
gas there through.
In still another embodiment, the mixture is aqueous and steps (a) and (c) include the step of mixing a metabisulphite therewith.
In still another embodiment, the mixture is aqueous and steps (a) and (c) include the step of establishing SO
2
in the mixture by mixing H
2
SO
3
therewith.
The term ‘oxidation mixture’ refers to a mixture of sulfur and oxygen, whose proportions are sufficient to cause ferrous ion to be converted to a ferric ion, for example at a range of conditions set out herein below.
Thus, the present invention provides a process by which materials, preferably sulphide materials, containing a base metal can be leached using ferric ion species, requiring relatively smaller quantities of ferric ion species by the use of oxidation mixtures of SO2 and oxygen to regenerate the ferric oxidant. Moreover, this can be achieved either in a one-step process or a two-step process. The two-step process can also be applied for heap or dump leaches. The present invention may also be applied to other materials such as those containing non-sulphide forms of the base metals such as naturally or non-naturally occurring materials containing the base metals in their metallic form.
In still another aspect of the present invention, there is provided a process of treating a base metal bearing host material comprising the steps of:
reacting the metal-bearing host material with a ferric ion species in a leach solution, thereby forming a ferrous ion species and transferring said metal to said leach solution; and
oxidizing the ferrous ion species with an oxidation mixture of SO
2
and oxygen to form the ferric ion species for subsequent reaction with the metal bearing host material.
In another aspect of the present invention, there is pr

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