1. School of Mining, Metallurgy and Chemical Engineering, University of Johannesburg, Johannesburg, South Africa
2. Informetrics Research Group, Ton Duc Thang University, Ho Chi Minh City, Vietnam
3. Faculty of Applied Sciences, Ton Duc Thang University, Ho Chi Minh City, Vietnam
4. School of Mining Engineering, University of the Witwatersrand, Johannesburg, South Africa