Study of lanthanum-didymium separation by solvent extraction from a liquor conditioned with lactic acid

Rare earth elements (REE) have increased in importance in the world due to the diverse applications in high-tech industries. The fact that Brazil has the world's second largest REE reserves makes it a potential producer of these elements. However, for that to occur, it is necessary to have knowledge about the production technologies of rare earths, mainly the technologies used in the refining stages, in which China predominates. Generally, the leached solution contains a mixture of REE and the main challenge is to improve selectivity during their separation and purification. For this reason, techniques to improve the efficiency of the separation of these elements have been widely studied in recent years. In the present study, we seek to define efficient routes for the separation of lanthanum (La) from didymium (Pr and Nd) by the solvent extraction technique (SX), using the organophosphorus extractant 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (P507) from a liquor conditioned with lactic acid. Isotherms were constructed using the McCabe-Thiele method to estimate the number of theoretical stages and the aqueous/organic ratio (A/O) necessary to achieve efficient separation during the process. In continuous solvent extraction experiments, REE recovery percentages and purity of didymium and lanthanum above 90% were obtained. Didymium with 99.9% purity was obtained in a circuit with nine extraction stages (extraction A/O ratio of 4:1) and seven scrubbing stages (scrubbing A/O ratio of 2:1). The results presented here show that the use of lactic acid can be a promising alternative to boost the efficiency of the solvent extraction process for the separation of these light rare earth elements.