In sulfide nickel deposits throughout the world, pentlandite and pyrrhotite
are commonly found together along with varying amounts of chalcopyrite and
platinum group minerals (PGMs). The mafic or ultramafic host silicates
associated with the sulfide mineralisation commonly exhibit a complex assemblage
of magnesium bearing silicates, many of which themselves contain significant
nickel. Four types of ore are proposed, each presenting their own processing
challenges. These are:
- economic grades of Ni, Cu and PGE (platinum group element) in a
pyrrhotite-bearing sulfide deposit, with low pyrrhotite to pentlandite
- economic grades of Ni, Cu and PGE in a pyrrhotite-bearing sulfide deposit, with moderate to high pyrrhotite to pentlandite ratios
- uneconomic high pyrrhotite: low tenor deposits
- low-grade low sulfide, high MgO ± PGE deposits that can sometimes be
economically mined and processed.
The grades and recoveries of nickel concentrates produced from sulfide ores can be significantly impacted by the ore mineral texture, the nickel tenor of the sulfides, and the polytype of pyrrhotite which may be either hexagonal (non-magnetic) or monoclinic (magnetic). The mineralogy of the silicates is also of great importance, especially the magnesium silicates and those which tend to produce particles which are asbestiform or which affect slurry viscosity. Other magnesium silicates such as serpentine carry nickel in solid solution, limiting the recovery entitlement of nickel by flotation because serpentine is not amenable to sulfide flotation mechanisms. Differences in plant flow sheets and reagent assemblages are required to effectively separate these minerals.
Experience from a variety of plant
operations and from extensive flow sheet development programs are discussed.
Examples are given of where significant improvements in nickel circuit
performance can be made by adjusting plant physical processing conditions or
process chemistry to compensate for measurable ore properties and
Lawson, V, Hill, G, Kormos, L and
Marrs, G, 2014. The separation of pentlandite from chalcopyrite, pyrrhotite and
gangue in nickel projects throughout the world, in Proceedings 12th AusIMM
Mill Operators’ Conference 2014, pp 153–162 (The Australasian Institute of
Mining and Metallurgy: Melbourne).