Regular Article

Solvent extraction process for the selective recovery of copper and cobalt from carrollite leach solution

¹ School of Metallurgy and Environment, Central South University, Changsha 410083, Hunan, PR China
² Department of Chemistry, Imperial College London, London SW72AZ, England

^* e-mail: wujianhui218@163.com

Received: 9 August 2018
Accepted: 25 September 2018

Abstract

A solvent extraction application consisting of three-sequential solvent extraction steps to selectively recover the copper and cobalt from carrollite leach solution was conceived and experimentally explored. The first step allowed the simultaneous extraction of 95.5% copper, 0.87% cobalt and 4.79% iron using 20% Lix984 in sulfonated kerosene and O/A ratio of 1 at initial pH of 2. Two-stage scrubbing at pH = 4 using diluted sulphuric acid solution allowed the removal of most of the cobalt (98.56%), iron (97.25%) and small amount of copper (0.36%). Complete stripping of copper was achieved at H₂SO₄ concentration of 1.5 mol/L and an O:A ratio of 1. This raffinate was the feed for the second step. The use 30% P204 in sulfonated kerosene, sodium-saponification rate of 30% and initial pH of 2.5 allowed the removal of 100% iron, 98.45% zinc, 93.64% calcium and 22.77% magnesium under the O:A ratio of 1 but with substantial co-removal of cobalt (8.23%). Two-stage scrubbing of this loaded organic phase at pH = 2.5 using diluted sulphuric acid solution allowed the extraction of most of the cobalt (92.75%). This raffinate was the feed for the third step. The simultaneous extraction of 99.08% cobalt, 5.12% magnesium and 2.87% nickel was found using 35% P507 in sulfonated kerosene, sodium-saponification rate of 65% and initial pH of 4 at an O:A ratio of 1:2. Two-stage scrubbing at pH = 3.5 using diluted sulphuric acid solution allowed the removal of most of the magnesium (96.82%), nickel (93.49%) and small amount of cobalt (2.87%). Complete stripping of cobalt was achieved at H₂SO₄ concentration of 1.0 mol/L at an O:A ratio of 3:1. Meanwhile, as long as the phase ratio (O/A) of extraction and stripping were properly controlled, this diluted cobalt solution can be concentrated before being sent to a subsequent step such as recovery of the metal by electrowinning. Based on the experimental results, a flowsheet for the extraction process is presented.