1. G.M. Ritcey, A.W. Ashbrook, Solvent Extraction, Elsevier, Amsterdam, 1979.
2. M. Meretukov, Process of Liquid Extraction in Colour Metallurgy, Metallurgia, Moscow, 1985, in Russian.
3. W.A. Rickelton, A.J. Robertson, D.R. Burley, Extraction process for removal of Co(II) from aqueous solutions, European Patent Application, 02 046 940, 1981.
4. Daihachi Chemical Industry, US Patent, 4,196,076, 1978.