The recovery of yttrium sulfate through antisolvent crystallization using alcohols

Abstract

The rare earth elements are used extensively throughout modern technologies due to their unique electronic properties. However, current recovery methods of these elements from leaching solutions are not economically feasible, therefore ongoing research is being conducted to establish alternative processes. Antisolvent crystallization is one of the proposed techniques where antisolvents such as alcohols are used to recover inorganic salts from aqueous solutions. For this study, yttrium sulfate [Y2(SO4)3] was used as model compound to investigate the effect of different short primary alcohols, i.e., methanol, ethanol, and 1-propanol, as antisolvents on the solubility of the salt under isothermal conditions at 23 °C. This work also featured thermodynamic simulations done by using OLI Studio. Experimental values were compared to the simulated data. All the alcohols investigated in this study were ultimately able to reduce the solubility of Y2(SO4)3 by over 99%. Experimental evaluation showed that the concentration of alcohol needed on molar basis was similar ethanol and 1-propanol, followed by methanol. The solid phase recovered from the suspension was experimentally found to be Y2(SO4)3·8H2O for all the alcohols. Lastly, a theoretical case study was done comparing the simulated data with experimental data extracted from literature for the recovery of REEs, which included Y3+, from a NiMH battery leach solution using alcohol. The Y3+ concentration of 1.3 g/kg, observed in the leach solution, was used for the case study in which ethanol was shown to be the most effective antisolvent needing only 0.89 kg (1.13 L) to achieve the maximum plateau yield of 92% from the 1 kg aqueous feed solution. A possible kinetic limitation for the crystallization of Y2(SO4)3 using ethanol as antisolvent was also identified.