A. A. Baba, O. Ajibola, A. S. Ibrahim, F. A. Adekola, R. O. Sanni, and Y. Abdulganiyu, “Upgrading of a Nigerian Ixiolite ore to Columbite by Sulphuric acid treatment”, Metall Mater Eng, vol. 22, no. 3, pp. 145–154, Sep. 2016.