Market Survey on Copper - Indian Bureau of Mines

c) Evaporation of water from the copper free electrolyte and precipitation of
nickel, iron and cobalt as sulphates from the concentrated solution. The nickel
sulphate is purified and sold for electroplating and other uses.
b) Hydrometallurgical Processes
Copper is most often found in form of sulphide minerals which undergo
pyrometallurgical operation to produce crude copper (blister copper) metal. But
the same is not true with copper oxide minerals. Oxide minerals when present
in sufficient quantity in the ore deposits can be smelted in blast furnace
economically as has been the practice in the past. However, oxide ores are too
low in copper to permit economical hydrometallurgical extraction. In addition,
many oxide minerals do not readily respond to froth flotation and therefore
need to be treated by non-pyrometallurgical route, preferably,
hydrometallurgical techniques. Hydrometallurgical extraction comprises
leaching, cementation/solvent extraction and electro winning.
Hydrometallurgical techniques are applied mainly to oxidised copper
ore, low grade oxide/sulphide mine wastes and roasted sulphide ores. Processes
have been developed to extract copper hydrometallurgically from sulphide
concentrates too.
Leaching Technology
Although leaching is a chemical process, physical factors play an important
role. The most important factor is the ingress of leach solution into the ore. There
are three types of voids in rocks - fractures, cleavage planes and fine pores. In most
copper bearing rocks, copper minerals are concentrated in fractures and cleavage
planes where solution can more readily come in contact with them than if they were
disseminated through the entire rock.
Diffusion is an important action in leaching. As the solution penetrates the
interior of the rock and dissolves copper minerals, a diffusion pressure is created and
soluble salts diffuse to a less concentrated solution at the surface of the rock.
The actual rate of dissolution depends upon the type of leaching and the
contacting conditions. Typical leaching cycles for oxidised ores are 5-12 hours for
fine concentrate with agitation leaching, 5-10 days for crushed particles in vat
leaching and 100-180 days in heap leaching. Factors favouring rapid leaching rates
are high acid strength, elevated temperature (up to 60 o C), large contact area and good
agitation.
Copper sulphide minerals dissolve mainly under extremely oxidising conditions
provided by high oxygen pressure.
The best solvent for oxidised minerals is sulphuric acid. It is cheap and can be
partly regenerated in leaching of sulphide/sulphite minerals. The best solvent for
sulphide minerals is acidified ferric sulphate.
In some cases, ammonia and hydrochloric acid are used for nickel-copper
sulphide ores/mattes. The leaching of sulphide ores with sulphuric acid as already
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