1. School of Chemical and Metallurgical Engineering, Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, South Africa
2. Department of Energy Resources Engineering, Inha University Yong-Hyun Dong, Incheon, Korea
3. Department of Mining Engineering, Federal University of Technology, Akure, Nigeria
4. Department of Civil and Mining Engineering, University of Namibia, Windhoek, Namibia