Geology Reference
In-Depth Information
Nickel carbonyl also provides an alternative option for the refining process. It
is gas formed by the reaction of carbon monoxide with nickel at low temperature
and pressure and nickel is selectively separated from its solid impurities. Nickel
carbonyl itself decomposes via a simple heating process and one of its constituents,
CO can be recycled for yet further production of nickel carbonyl (IPPC, 2009).
Fig. 8.5 shows diagrammatically the processes associated with the production
of nickel from sulphide ores.
Fig. 8.5 Nickel production from sulphide ores (IPPC, 2009)
8.7.2 Nickel laterites process
Limonite laterites are made up of iron oxides (goethite) composed of 47-59% Fe,
0.8- 1.5% Ni and a valuable trace Co content. Saprolite laterites, form beneath the
limonite zone and are of the silicate type. They typically contain 1.5-2.5% nickel.
The high content of iron and magnesium oxides or silica in both laterites make the
upgrading concentration process di
cult, as does their high moisture content that
must be dried off (Dalvi et al., 2004; Schellmann, 1983; Golightly, 1981). Therefore,
a rotary kiln furnace is used to preheat, dry and calcine the high magnesium content
of the ore. Then the process continues, as in the case of sulphide ores,with smelting
electric furnace, converter, ferric chloride leaching and electro-winning treatments.
Due to the high iron content in the matte, a converter is commonly used to pro-
duce ferronickel. High temperature ammoniacal leaching with hydrogen reduction
(the Caron process) and high pressure sulphuric acid leaching (HPAL) are two al-
ternative routes as already described above. HPAL plants are very versatile, though
more complex and expensive. They necessitate intensive amounts of energy to heat
the ore and produce the acid. Moreover, the maintenance of equipment given its
contact with hot acid and their environmental impact (they produce salts of heavy
metals as byproduct) are also important issues.
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