Insights into non-aqueous solvent extraction of gadolinium and neodymium from ethylene glycol solution using Cyanex 572

Abstract

Comparison of the separation factors for Gd(III) over Nd(III) extraction from aqueous and non-aqueous ethylene glycol solutions using Cyanex 572 in kerosene. • Addition of water bridges the gap between hydrometallurgy and solvometallurgy. • Extraction of Gd(III) and Nd(III) from non-aqueous solution was compared with aqueous solution. • Gd and Nd extraction increases with increasing Cyanex 572 extractant concentrations. • Temperature had almost no effect on the extraction of both metal ions. • Under certain conditions, maximum separation factor was obtained and reached 22.09. The reprocessing of rare earth elements (REEs) by conventional hydrometallurgical processes remains a challenge because of the difficulties of separation. Solvometallurgy is a new non-aqueous solvent extraction approach including two immiscible organic phases which has been advanced for the extraction of rare earths. The less polar organic phase (LP) was a solution of Cyanex 572 (Cy-572) as an acidic extractant dissolved in kerosene. Whereas, the more polar organic phase (MP) was ethylene glycol with a limited amount of water dissolved in metal nitrate salts and lithium nitrate as a salting-out agent. The extraction of Gd(III) and Nd(III) from ethylene glycol solution was compared with extraction from an aqueous solution. The solvent extraction equilibrium was estimated by slope analysis method, and the composition of the Gd(III) extracted species in the less polar phase was proposed to be Gd(OH) L 2 . 2 HL ¯ . The non-aqueous system performs better separation of rare earths than the corresponding conventional extraction system. Subsequently, 0.1 mol/L HCl is the best stripping agent for both metal ions after two steps from the less polar phase, while a solution composed of 10% HF + 0.05 mol/L HCl is superior for nearly complete separation between the two elements. Eventually, the separation of binary mixtures of Gd(III) and Nd(III) is possible by this new non-aqueous solvent extraction system. A complete flow sheet process including extraction, scrubbing and stripping steps for the separation of Gd(III) and Nd(III) was proposed.