Geology Reference
In-Depth Information
Saprolite ores are smelted with sulphur in order to reduce the oxide to nickel
sulphide matte and the iron oxide is removed in the slag. Then the process continues
as in the case of sulphide ores by using either precipitation or solvent extraction
methods and finally electro-winning or hydrogen reduction.
Open heap leaching can offer a feasible alternative to rock laterites treatment.
The process consists of percolating sulphuric acid into crushed ore located in na-
tural heaps on an impervious liner. Such ore must have a low content of clay to
maintain permeability. First, acid is sprayed onto the heaps and left in-situ for sev-
eral months until the pregnant solution reaches a 60-70% nickel-cobalt-zinc-copper
content. Once this occurs, the solution is neutralised with limestone to produce the
hydroxide which can be conventionally smelted. The problem with this process is
that the acid consumption can be as high as 1000 kg per tonne of ore treated. As
ore grades decline, this fact limits its commercial possibilities. The plant and mine
infrastructure are however cheaper than the HPAL process. In fact, except for one
in Finland, for the treatment of sulphides (Kuck, 2003), there are no commercial
plants in operation for nickel heap leaching.
Fig. 8.6 shows in a diagram the processes associated with the production of
nickel from laterite ores.
Fig. 8.6 Nickel production from laterite ores (IPPC, 2009)
8.7.3 Energy and environmental issues
According to the IPPC (2009), the principal emissions to air of nickel and cobalt
smelting are carbon and sulphur dioxides, NO
x
and other acidic gases, metals and
their compounds including As, chlorine, VOCs, CO, carbonyls, dust and odours.
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