In this work, physical, physicochemical and biological processes were combined to decrease the sulfur and ash content of finely ground coal. Two separation methods - flotation and a multigravity separator (MGS) - were studied to determine the optimum conditions of separation. The results showed that it is possible to obtain clean lignite that contains 34.36% ash and has a 77.39% combustible recovery by using MGS and 39.22% ash with a 37.38% combustible recovery by using flotation techniques. When the MGS and flotation products were treated by biological methods, the total sulfur contents of lignite were reduced by 54.39% and 47.08%, respectively, whereas the ash contents of MGS and flotation product were decreased by 67.61% and 60.95%, respectively. (C) 2014 Elsevier Ltd. All rights reserved.