The Masking of Cobalt by Sulfite Ion in Solvent Extraction.

Abstract

After leaching cobalt crusts in an ammoniacal solution using sulfur dioxide gas as a reductant, the extraction of cobalt was held down in the solvent extraction process. The effects of sulfite ion on cobalt were studied by using nitroso R salt which forms a complex with cobalt. As a result, formation of cobalt complex salt was negligible in the solution of ammonium sulfite and sodium sulfite. It is supposed that sulfite ion acts as a masking reagent for cobalt.Solvent extraction of cobalt and nickel was carried out using LIX84-I as an extractant for the solution of ammonium sulfite. The effects of the ammonium sulfite concentration and retention time on the extraction of cobalt were investigated. Cobalt (10 ppm) was not extracted from the ammonium sulfite solution of concentration more than 0.5 M and the pH over 10.5. In the same condition, nickel (10 ppm) was extracted completely. Same studies were carried out by using PC-88A and D2EHPA, but superior separation of cobalt and nickel was not attained.An EDTA titration was carried out by addition of sodium sulfite or ammonium sulfite to the solution including cobalt and nickel. As a result, only nickel was titrated quantitatively inthe mixed solution containing up to 1 mg (20 ppm) of cobalt