Recovery of yttrium and lanthanides from sulfate solutions with high concentration of iron and low rare earth content

Abstract

To overcome the low recovery, generally obtained for the heavy and middle rare earth elements (HREE and MREE) by sodium double sulfate precipitation, the recovery of the MREE and HREE as phosphate salts was investigated. High recovery yields (≥ 95%) were obtained even for sulfate solutions containing low concentrations of REE and a high concentration of iron(II). The influence of many industry-relevant parameters (temperature, pH, stoichiometric excess of phosphate, aluminum contamination, residence time) is discussed in order to optimize the REE recovery and to minimize the precipitation of iron. The developed process was also validated in continuous operation at a pilot scale. Finally, the REE phosphate concentrate could be converted into REE hydroxides which allows its dissolution into diluted HCl. Taking into account the phosphate precipitation, the conversion into hydroxides and the dissolution in HCl(aq), high recovery yields were obtained for Y, Gd and La (68%, 77% and 86% respectively). The results show that it is possible to economically obtain purified REE solutions starting from industrial solutions which are usually discarded.