Solvent extraction process for the recovery of nickel and cobalt from Caldag laterite leach solution: The first bench scale study

Abstract

A solvent extraction application consisting of two-sequential solvent extraction circuits to separate the nickel and cobalt from a synthetic sulphate leach solution which simulates a typical Caldag lateritic leach solution was conceived and experimentally explored. The first circuit allowed the simultaneous extraction of most of the nickel (98%), cobalt (98%) and manganese (94%) with 20% neodecanoic acid (Versatic 10) and 5% tri-n-butyl phosphate (TBP) in ShellSol 2046 at pH7.2 together with substantial amounts of calcium (65%) and magnesium (12%). Three stages of scrubbing at pH5.6 using diluted sulphuric acid solution allowed the removal of most of the magnesium (90%) and substantial amount of calcium (16%). Complete stripping of nickel, cobalt, manganese, magnesium and calcium was achieved at pH0.75. This loaded strip solution was the feed for the second circuit. The use 15% bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272) and 5% TBP in ShellSol 2046 allowed the extraction of most of the cobalt (94%) and manganese (98%) at pH5.0 but with substantial co-extraction of magnesium (41%) and calcium (40%) and a minor amount of nickel (3%). A two-stage scrubbing of this loaded organic with cobalt (20g L−1) solution was performed. Magnesium, calcium and nickel were completely displaced with cobalt. Most of the manganese (93%) was removed from the organic. Complete stripping of the cobalt and manganese in the scrubbed organic phase was achieved at pH1.0. Therefore, nickel (94%) and cobalt (91%) were totally separated from the feed solution. In addition, slope analyses were carried out to determine the nature of the extracted complexes of the nickel and cobalt with each extractant. Based on the experimental results, a flowsheet for the separation process is presented.