Reverse flotation of a subbituminous coal/gangue mixture and the effect of various factors on the reverse flotation have been investigated. The results showed that the separation of coal from gangue by reverse flotation was possible and good selectivity was achieved, but up to 6 kg/t of DTAC (dodecyltrimethyl ammonium chloride) were needed. In addition, the separation could only be achieved through stage additions of DTAC. Otherwise, even higher dosages of the collector could not provide a good separation. Dextrin was needed to depress coal, so the selectivity was improved. The selectivity was further enhanced by addition of a ferric silicate hydrosol which activates calcite and dolomite in a cationic flotation. Conditioning with the ferric silicate hydrosol promoted the activation. The flotation was best in alkaline pH range. (c) 2005 Elsevier Ltd. All rights reserved.