South African Journal of Chemical Engineering (Jul 2024)
New experimental findings on the separation of cobalt and nickel from an ammonia-ammonium-based leach liquor using ammonium-saponified Cyanex 272
Abstract
There is a need to improve cobalt and nickel recovery from industrial waste streams such as secondary leach solutions and rechargeable battery leach solutions due to the increasing economic value of these critical metals. Ammonia is an important lixiviant due to its limited environmental impact compared to acid based lixiviants, however, the subsequent selective extraction of cobalt and nickel from the leach liquor is a major challenge. This study presents new experimental findings on the treatment of a Base metal Refinery (BMR) secondary leach liquor that contains high concentrations of ammonia and ammonium sulphate, and low concentrations of cobalt (∼442 mg/L) and nickel (∼1624 mg/L) using partially saponified Cyanex 272. New knowledge that can be applied in the treatment of ammonia based leachates from various industrial wastes that contain residual cobalt and nickel is presented herein. The investigation was conducted through the determination of the optimum extraction temperature, percentage saponification, and organic to aqueous ratios. Partial saponification of Cyanex 272 increased ammonia-metal complex stability at the interphase and this limited cobalt extraction between 30 °C and 50 °C. However, a high cobalt extraction percentage, and a high separation factor of 94.07 %, and 1189.76 respectively were achieved at 60 °C, 20 % saponification, and 0.5 O/A loadings in a single contact. A second-stage batch extraction produced a nickel aqueous stream with no cobalt. Stripping of the loaded organic phase with dilute sulphuric acid produced a pure cobalt aqueous stream. Further, the extractant was successfully regenerated post stripping. Overall, partial ammonium-saponification increased the extent of cobalt extraction, and selectivity. The novel process conditions reported herein can be used to design sustainable cobalt-nickel separation processes.
