Extraction of rare earth elements from their oxides using organophosphorus reagent complexes with HNO 3 and H 2O in supercritical CO 2

Abstract

Direct extraction of metals from solids with complexing agents in supercritical CO 2 (SC-CO 2) has recently attracted interests in separation, purification, recovery, and analysis of metals. In the present study, the static/dynamic extraction of rare earth elements (Nd, Ce) from their oxides (Nd 2O 3, CeO 2) with organophosphorus complexes with HNO 3 and H 2O in SC-CO 2 was investigated. The static extraction efficiency of Nd from Nd 2O 3 with the tri- n-butylphosphate (TBP)-HNO 3 complex could reach 95% under optimized experimental conditions. However, the static extraction efficiency of Nd from Nd 2O 3 with the trilkyl phosphine oxide (TRPO)-HNO 3 complex was less than 10%, and the static extraction efficiency of Ce from CeO 2 with the TBP-HNO 3 complex was less than 1%. The dynamic extraction efficiency of Nd from Nd 2O 3 with the TBP-HNO 3 complex could reach more than 97%. Effects of parameters were evaluated on the extraction efficiency to ascertain the optimum conditions. This study illustrated the extraction process using the TBP-HNO 3 complex in SC-CO 2 would be feasible for separation, purification, recovery, and analysis of some rare earth elements from various oxide mixtures.