The possibility of cleaning a lignite by the froth flotation method was studied. Laboratory tests were carried out and the influence of various surfactant additions, feed particle size, pulp density and system pH on process performance was investigated. The feasibility of separating coal and refuse was determined from the coal recovery-ash reduction curves, while the quality of the products was evaluated by proximate and ultimate analyses, as well as mineralogical and chemical analyses of the ashes. The phenomenon of reverse flotation was observed through the whole work. Within the range studied, the optimum particle size was - 300 + 75 mum, the pulp density was 15% and the froth dosage was 0.4 g/kg coal. The use of kerosene alone as a collector neither improved the total recovery nor enhanced the selectivity. In contrast, addition of surfactants without any kerosene resulted in lower product ash levels. The ash/yield performance of cationic, non-ionic and anionic surfactants was higher in acidic, neutral and alkaline solutions, respectively, however the overall performance of cationic surfactants was better. Zeta potential measurements contributed to the understanding of these effects. (C) 2001 Elsevier Science B.V. All rights reserved.