Pentlandite and serpentine specimens were obtained from a sample of an ultramafic deposit to explore interactions that might be factors in processing by flotation. Zeta potential was measured under conditions designed to progressively approach the environment under which flotation will be attempted: viz. pentlandite and serpentine alone with indifferent background electrolyte; pentlandite conditioned in the presence of serpentine with indifferent background electrolyte; pentlandite conditioned in the presence of serpentine with supernatant derived from an ore suspension as background electrolyte. The "single mineral" experiments showed that hetero-aggregation is expected and was confirmed in the "mixed mineral" experiments. In the presence of supernatant uptake of Mg(OH)(2) precipitates was detected and confirmed by tests using solutions doped with Mg ions and by surface analysis using scanning electron microscopy. (C) 2015 Elsevier Ltd. All rights reserved.