1. National Engineering Research Center of Coal Preparation and Purification, China University of Mining and Technology, Xuzhou 221116, Jiangsu, P. R. China
2. School of Chemical Engineering and Technology, China University of Mining and Technology, Xuzhou 221116, Jiangsu, P. R. China
3. Key Laboratory of Coal Processing and Efficient Utilization of Ministry of Education, China University of Mining and Technology, Xuzhou 221116, Jiangsu, P. R. China