1. 1Key Laboratory of Mine Disaster Prevention and Control, College of Mining and Safety Engineering, Shandong University of Science and Technology, Qingdao, Shandong 266590, China, Tel./Fax: +86 532 86057617
2. 2Key Laboratory of Mine Disaster Prevention and Control, College of Mining and Safety Engineering, Shandong University of Science and Technology, Qingdao, Shandong 266590, China
3. 3College of Resources and Environmental Engineering, Binzhou University, Binzhou, Shandong 256603, China, Tel.: +86 543 3191865, Fax: +86 543 3190000
4. 4College of Chemical and Environmental Engineering, Shandong University of Science and Technology, Qingdao, Shandong 266590, China
5. 5College of Resources and Environmental Engineering, Binzhou University, Binzhou, Shandong 256603, China
6. 6Institute of Safety and Science Engineering, Henan Polytechnic University, Jiaozuo 454000, China