1. Solvent Extraction, Principles and Applications to Process Metallurgy;Ashbrook,1979
2. Ventron, G., Societé Française des Petroles BP, Eur. Patent Appl. No. 0,023,428, 1979.
3. Schimmel, G., Krause, W., Gradl, R., German Patent No. 31,27,900, 1981.
4. Karlsson, B.G., U.K. Patent Appl. No. 2,001,618, 1978.