Solvent extraction in hydrometallurgy: the role of organophosphorus extractants

Solvent extraction (SX) has come to be one of the most important separation processes in hydrometallurgy. Phosphorus-based extractants have proved to be of particular importance, especially for the separation of cobalt from nickel. However it was not until the dialkyl phosphinic acid reagent, CYANEX 272, and its dithio analogue CYANEX 301, became available that liquors containing very low Co:Ni ratios of at least 1:40 to even >1:100 could be treated. This has opened the way to the direct application of SX for the separation of Co from Ni in liquors derived from the leaching of nickel mattes from the smelting of nickel sulphide ores and from the pressure acid leaching of nickel laterite ores. This paper describes the development of the range of Cytec extractants and, in particular, discusses the development of their application for the separation of cobalt from nickel. Examples of actual industrial operating plants will also be given and individual flowsheets discussed.