The presence presence of ions in plant water is believed to be having an effect on the flotation process as ions are able to modify the chemistry of the system. This study investigated the interactive effects of ionic strength, depressant dosage and depressant type on the recovery of copper and nickel sulphides, water, floatable and entrained gangue as well as grade of the valuable sulphides in the flotation of a Pt bearing ore from the Merensky reef. Batch flotation results showed no change in Cu recovery, but Ni recovery decreased dramatically when a polysaccharide depressant was charged at 500 g/t. Water recovery increased with increasing ionic strength, indicating that there exist ions in the water system which have a froth stabilising effect. (C) 2012 Elsevier Ltd. All rights reserved.