1. Department of Chemical Engineering, KU Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium
2. National Engineering Research Centre of Coal Preparation and Purification, China University of Mining and Technology, Xuzhou 221116, Jiangsu, China
3. State Key Laboratory of Urban Water Resource and Environment, School of Environment, Harbin Institute of Technology, Harbin 150090, P. R. China