1. Department of Chemical, Metallurgy & Materials Engineering, Tshwane University of Technology, P.M.B. X680, Pretoria 0183, South Africa
2. Department of Industrial Engineering, Tshwane University of Technology, P.M.B. X680, Pretoria 0183, South Africa
3. Department of Industrial and Systems Engineering, Cape Peninsula University of Technology, Cape Town 7500, South Africa