The distribution coefficients of Y3+ and Eu3+ between HNO3 and HDEHP

Abstract The recovery and purification of rare earth metals from electronic waste is an attractive alternative to environmentally damaging virgin mining of these metals, as the concentrations of rare earth metals are significantly higher in electronic waste than can be found naturally. It is therefore prudent to develop recycling and purification processes for these metals from electronic waste. Solvent extraction is the most commonly used technique for the purification of rare earth metals, as solvent extraction is capable of handling large volumes while maintaining high product purities. Since there is a scarcity of thermodynamic phase equilibrium data that can assist in developing such recycling processes, this study begins a series of investigations to address this gap. The distribution coefficients of Y3+ and Eu3+ ions between an organic phase and an aqueous nitric acid solution, as a function of the nitric acid concentration, were measured at approximately 298 K. These are reported for systems containing an organic phase of di-(2-ethylhexyl) phosphoric acid (HDEHP) in a diluent; varying either the diluent or the concentration of the HDEHP. The two diluents investigated were n-nonane and n-dodecane. Measurements were conducted in a liquid-liquid equilibrium cell, with the concentration of the rare earth metals determined by ICP-OES analysis. The distribution coefficients for Y3+ and Eu3+ were shown to be inversely proportional to the aqueous acid concentration, and dependent upon both the concentration of the HDEHP in the organic phase and the diluent used. The data were used for the optimisation of a rare earth metal extraction column.