Cobalt and Nickel Separation in Nitric Acid Solution by Solvent Extraction Using Cyanex 272 and Versatic 10

Abstract

Recent trend in extraction of nickel and cobalt from laterite ore through hydrometallurgical route is by using leaching agents that can be effectively regenerated, such as hydrochloric and nitric acid. Despite success stories of nickel laterite leaching in nitric acid, investigations on separation of nickel and cobalt from pregnant leach solution in this leaching media are still poorly reported. Nickel and cobalt are mostly recovered in the forms of intermediate products such as mixed hydroxide precipitate (MHP) and mixed sulphide precipitate (MSP). In this paper, separations of cobalt and nickel in nitrate solution and in pregnant leach solution of nickel laterite ore from Indonesia are discussed. Series of solvent extraction tests using Cyanex 272 and a combination of Versatic 10 and Cyanex 272 were performed under variations of equilibrium pH, extractant concentration, temperature and volume ratio of organic to aqueous phase (O/A ratio). The investigation results demonstrate that Cyanex 272 can be effectively used to separate cobalt and nickel in a solution with low nitrate concentration at the absences of Fe and Mg. The increase of equilibrium pH, extractant concentration, O/A ratio and temperature tends to enhance cobalt extraction and co-extraction of nickel. The best condition for separation of Co and Ni was obtained at equilibrium pH of 5, Cyanex 272 concentration 20% (v/v), temperature 25oC and O/A ratio 1/1. Separation of Co-Ni and Mg from pregnant leach solution can be well performed by 2 stage-SX using Versatic 10 followed by Cyanex 272 and selective stripping of loaded organic from the second stage of the extraction by using 1 molar sulfuric acid.