Flotation of a low grade pentlandite ore containing large amounts of serpentine minerals from Western Australia was conducted with process water having high ionic strength. Nickel recovery was low in the flotation of both fine and coarse fractions. X-ray photoelectron spectroscopy (XPS) analysis indicated that oxidation occurred on both fine and coarse pentlandite particles. To reduce pentlandite oxidation, sodium hydrosulphide (NaHS) and dithionite (Na(2)S(2)O(4)) were added during grinding. It was found that NaHS improved both pentlandite and serpentine mineral flotation and deteriorated pentlandite separation from serpentine, whilst Na(2)S(2)O(4) improved pentlandite flotation without affecting serpentine flotation and therefore increased pentlandite separation from serpentine. (C) 2010 Elsevier Ltd. All rights reserved.