Separation and recovery Nd and Dy from Mg-REEs alloy by vacuum distillation

Abstract

Liquid metal extraction (LME) is considered to be one of the alternatives for green production of rare earth elements from secondary resources. It leads to shift paradigm to eco-friendly economy to reduce carbon footprint and support sustainable development. However, separation of rare earths elements (REEs) from generated magnesium (Mg)-REEs after LME process is still remained as vacant technology due to lack of databases. In this work, fundamental investigation on the mechanism and kinetics for separation of REEs from Mg-REEs alloys by vacuum distillation is proposed. Experimental parameters of the process are thermodynamically designed at 2.0 × 10−5 atm in the range of 600 °C to 900 °C for selective distillation of Mg. Mg distillation is observed with gradual phase transformation from raw materials to phases including less Mg. 99.5 % yield of REEs and 99 % of pure Mg are successfully recovered as the metallic state, respectively. Interestingly, relatively rapid separation behavior of dysprosium (Dy) than neodymium (Nd) is observed and evaluated by variation Gibbs free energy and heat of mixing enthalpy based on the unique databases from practical experiments. It is indicated that the kinetics of phase transformation shows the different distillation behavior between individual REEs through thermodynamic and experimental assessments even if REEs group shares similar chemistry properties. This investigation can provide fundamental databases for grafting vacuum distillation after LME to secure sustainability for recycling industry.