Lozano, L. J., and J. García. “Recovery by Solvent Extraction of Vanadium from Spent Catalysts Leaching Solutions Using Primene 81R”. Revista De Metalurgia, vol. 37, no. 5, Oct. 2001, pp. 582-90, doi:10.3989/revmetalm.2001.v37.i5.524.