Organic solvent-assisted crystallization of inorganic salts from acidic media

BACKGROUNDSolvent displacement crystallization (SDC) provides an energy-efficient alternative to evaporative crystallization potentially leading to crystal products of superior quality, both in terms of purity and size, due to better supersaturation control. The present work investigates the SDC process in terms of appropriate organic solvent selection and application to several metal (K+,Na+, Mg2+ Fe2+, Cu2+, Ni2+, Co2+, Zn2+, Fe3+ and Al3+) sulfate and chloride systems of hydrometallurgical interest. RESULTSCriteria for the screening of organic compounds with suitable physical and chemical properties have been established and 2-propanol was selected as an effective salting out agent to precipitate crystalline metal sulfates of practical interest; differences in crystallization behaviour among the various salts were linked to the hydration energy of the cation. None of the tested metal chlorides could be successfully separated, due to enhanced metal chloride solubility in non-aqueous solvents relative to water by formation of chloro-complexes with larger stability constants. CONCLUSIONSThe solvent displacement crystallization process was investigated and selection criteria for the organic solvent were established. 2-propanol proved to be the most effective salting out agent for metal sulfates resulting in>90% cation removal. By contrast none of the metal chlorides could be successfully separated due to salting-in behaviour. (c) 2014 Society of Chemical Industry