Selective removal of impurities from rare earth sulphuric liquor using different reagents

In order to obtain a marketable rare earth product, purity requirements need to be met. More specifically, purification needs to be undertaken before precipitation. This addresses the technical feasibility of the use of different reagents such as limestone, lime, sodium hydroxide and magnesium oxide, to purify a rare earth sulphuric liquor containing impurities such as Ca2+, Mg2+, Mn2+, Fe3+, Al3+, Th4+, UO22+, SO42- and PO43-. Moreover, it is important to avoid significant losses of rare earth elements during purification. To achieve this, experimental batch tests were carried out and the results obtained suggest that the best procedure for chemical precipitation requires neutralization in two consecutive steps: (i) limestone should be added until the pH level is about 3.5 and (ii) calcium hydroxide or lime is dosed until pH level rises to approximately 5.0. Under this optimum condition, some relevant impurities were fully removed, namely Fe, P, Al and Th. Also, about 98% of the initial uranium was removed, reaching the lowest uranium to rare earth oxides (REOs) mass ratio in the purified rare earth liquor considering all the experiments performed. Likewise, this was the condition in which the lowest sulphate content and U/REOs mass ratio in the purified rare earth liquor was obtained. Furthermore, the rare earth oxides recovery reached about 85%, preserving the same light (La + Ce + Pr + Nd)/total rare earth mass ratio observed in the purified liquors when compared to what was noticed in the initial rare earth sulphuric liquor. Moreover, the purified liquor is suitable to produce marketable rare earth salts to be processed in solvent extraction or ion exchange units.