[Wang, Shuyun] Univ South China, Sch Environm Protect & Safety Engn, Hengyang 421001, Peoples R China.^[Xie, Xionggang] Guizhou Univ, Min Coll, Guiyang 550004, Peoples R China.^[Chen, Xi] Univ South China, Chuanshan Coll, Hengyang 421001, Peoples R China.