1. The
Key Laboratory of Water and Sediment Sciences, Ministry of Education,
College of Environmental Sciences and Engineering, Peking University, Beijing 100871, P. R. China
2. Department
of Mineral Resources and Energy Engineering, Chonbuk National University, 567, Baekje-daero, Deokjin-gu, Jeonju, Jeonbuk 561-756, Republic of Korea