Pentlandite-lizardite interactions and implications for their separation by flotation

Magnesium silicate bearing minerals, such as lizardite, are known to cause problems in the flotation of nickel sulfide ores (e.g. pentlandite), by adhering to the valuable mineral particles. Addition of the polymeric dispersant, carboxymethyl cellulose (CMC), has been found to improve nickel recovery during flotation. The interaction between lizardite and pentlandite has been directly investigated using the atomic force microscope (AFM) and electro-kinetic zeta potential determinations, as a function of pH and in the presence of CMC. The lizardite mineral was positively charged, with the zeta potential independent of pH. The magnitude and sign of the pentlandite particles were pH dependent and were negative for pH values above 4.5. At pH values larger than 9, where flotation of nickel sulfide ores is routinely performed, the two minerals are oppositely charged and therefore attract through an electrostatic mechanism. Direct interaction force measurements between pentlandite and lizardite surfaces as a function of pH demonstrate this attractive interaction. Adsorption of CMC at the lizardite/solution interface overcompensates the positive charge on the lizardite particle and its zeta potential is rendered negative. In the presence of CMC, a repulsive interaction force between lizardite and pentlandite was measured in the AFM, which was concluded to be of electro-steric origin. The results explain the flotation behaviour of the minerals performed in this, and previous, studies.