Hydrophobic polystyrene nanoparticles (latex) were evaluated as replacement collectors for pentlandite flotation with a view to improving processing of ultramafic ores. Nanoparticles adsorb onto pentlandite particles, rendering them sufficiently hydrophobic to induce flotation. Polystyrene nanoparticles bearing surface imidazole groups specifically bind nickel ions and appear to improve selectivity (i.e. nickel grade), presumably because of chelation interactions between the imidazole groups and the pentlandite surface. Very high nanoparticle concentrations were required for high pentlandite recoveries under the high ionic strength conditions typically used in industry because the nanoparticles were'coagulating. The path to commercially relevant nanoparticle flotation collectors involves increasing the colloidal stability of the nanoparticles while minimally impacting hydrophobicity. (C) 2013 Elsevier B.V. All rights reserved.