1. Clean Technology and Applied Materials Research Group, Department of Chemical and Metallurgical Engineering, Vaal University of Technology, Private Bag X021, Vanderbijlpark 1900, South Africa
2. Eskom Power Plant Engineering Institute (EPPEI) Specialisation Centre for Emission Control, School of Chemical and Minerals Engineering, Centre of Excellence for Carbon-Based Fuels, North-West University, Private Bag X6001, Potchefstroom 2520, South Africa