1. KEN Research Center, SeoKyeong University, Seoul 136-704, Republic of Korea
2. Department of Metallurgical and Materials Engineering, The University of Texas at El Paso, 500 West and University Avenue, El Paso, TX 79968-0520, USA
3. National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China