Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Patent
1993-10-21
1995-03-14
Rosenberg, Peter D.
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
C22B 111, C22B 304
Patent
active
053973801
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for recovering metal values from metal sulphide materials, and particularly from refractory materials, complex copper concentrates and nickel concentrates that contain precious metals.
2. Description of the Related Art
Sulphide material can be processed totally hydrometallurgically, for instance by means of a combination of leaching stages and a subsequent stage in which the leached metal values are recovered with the aid of such methods as liquid extraction, chemical precipitation or electrolysis (electrowinning). Leaching of sulphides can be carried out with oxidizing solvents, such as iron(III)sulphate. A leaching process of this kind, however, is extremely slow and requires considerable space, and is therefore preferably performed outdoors. The sulphides may also be leached subsequent to roasting the sulphides, which converts the valuable metal content to forms which are more readily dissolved and which can be carried out, for instance, in the form of a sulphating or chlorinating roasting process. Sulphide material can also be leached directly with atmospheric oxygen or an oxidation agent, for instance in a sulphuric acid environment under high temperature. A leaching process of this nature must therefore be carried out at elevated pressure in an autoclave. Two reactions occur when pressure leaching in a sulphuric acid environment, these being: is not normally possible to avoid reaction (2), and consequently the leaching product will contain elemental sulphur (S.sup.0), which is liable to complicate both the leaching process concerned and also continued leaching of the leaching residue, due to inactivation of the surface of the leached material by precipitated sulphur. Pressure leaching has not been used industrially to any appreciable extent, because of the problems indicated above.
Leaching of sulphidic material with atmospheric oxygen can also be carried out in the presence of bacteria as "catalyzing" auxiliaries. In general, these bacteria are comprised of Thiobacillus Ferrooxidans, which encourage the oxidation of both sulphur and iron. Bacteria-based leaching processes are normally carried out with the intention of recovering metals according to one of the following alternatives, both of which are applied on an operational scale in many places in the world.
1. Leaching with the intention of leaching out valuable metals, which are then recovered selectively from the leaching solution with the aid of conventional hydrometallurgical methods. Examples: copper, nickel, cobalt, uranium, zinc.
2. Leaching of so-called refractory minerals that contain precious metals (such as pyrite and arsenopyrite) so as to free the precious metals, which are then extracted from the leaching residue (e.g. cyanide leaching) by means of conventional hydrometallurgical methods.
Bacteria leaching affords certain advantages over pressure leaching, among other things because the bacteria encourage or favour oxidation of both sulphide sulphur and elemental sulphur to sulphate. The oxidation of Fe(II) to FE(III) is also encouraged. The bacteria-leached material can therefore be subjected to further leaching, e.g. with cyanide, to recover precious metals from the first leaching residue, without risk of problems caused by elementary sulphur. One serious drawback, however, is that bacteria leaching requires very long leaching times in order to achieve sufficiently high metal yields. This will be exemplified in the following with reference to the recovery, or winning, of precious metals from so-called refractory materials, although the problem applies generally to the majority of the sulphide materials in question.
Precious metals, particularly gold, are often present in the form of submicroscopic grains embedded in "host minerals" such as pyrite and arsenopyrite. Hydrometallurgical recovery of precious metals from these materials is attractive in most cases, and is preferred to pyrometallurgical processes, which, from a technical and
REFERENCES:
patent: 3293027 (1966-12-01), Mackiw
patent: 3954450 (1976-05-01), Kuhn
patent: 4362607 (1982-12-01), Ritcey
patent: 5232491 (1993-08-01), Corrans
patent: 5246486 (1993-09-01), Brierley
Petersson Stig A.
Sandstrom Ake
Boliden Mineral AB
Rosenberg Peter D.
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