1. School of Chemical Engineering and Technology, China University of Mining and Technology, Xuzhou 221116Jiangsu ,China
2. National Engineering Research Center of Coal Preparation and Purification, China University of Mining and Technology, Xuzhou 221116Jiangsu ,China
3. Department of Earth Resources Engineering, Faculty of Engineering, Kyushu University, 744 Motooka, Nishiku, Fukuoka 819-0395, Japan