The flotation of millerite — A single mineral study

While pentlandite is the dominant nickel sulphide mineral recovered from nickel ores, other nickel sulphide minerals can often be present. One such rare but important nickel sulphide mineral is millerite (NiS). There is very little information in the literature about the flotability of millerite, in particular its flotation behaviour relative to that of pentlandite under different flotation conditions. This paper details a single mineral investigation into the flotability of millerite, and compares its flotability with that of pentlandite and other nickel arsenides often present in nickel sulphide ores.Millerite was found to be strongly flotable with xanthate collector at pH 9 but there was a noticeable decrease in recovery at pH 10 and a further decrease at pH 10.5. Size-recovery data suggests the recovery of millerite decreases at sizes above 75 μm and below 10 μm. In particular, fine millerite floats poorly in a similar fashion to fine pentlandite.At pH 9 with xanthate collector millerite exhibits a lower limiting threshold potential at about − 100 mV SHE, about 300 mV below the lower limiting threshold potential for pentlandite.Millerite is not readily depressed by cyanide at pH 9 and further, cyanide doses required to affect depression are much higher than those required to depress the nickel arsenide mineral gersdorffite. Cyanide should therefore be a suitable depressant for the separation of gersdorffite from other nickel sulphide minerals such as millerite and pentlandite.

Research Highlights► Little literature on the flotation behaviour of millerite. ► Its behaviour in single mineral flotation tests has been identified. ► Parameters considered include Eh, pH, particle size and added depressants. ► Suggestions for separating penalty minerals from millerite proposed.