Different separation techniques such as solvent extraction, ion exchange, and precipitation are often used for recovery of rare earth elements (REEs) from pregnant leach solutions obtained from acid leaching. Solvent extraction is generally accepted as the most appropriate commercial technology for separating REEs due to the need to be able to handle larger volumes of diluted pregnant solutions. This study focused on the development of selective separation of light and heavy REEs from the pregnant leach solution obtained from leaching of apatite ore in 1 M sulfuric acid (H 2 SO 4) using solvent extraction. Three different commercial organophosphorus extractants (di-(2-ethylhexyl) phosphoric acid (D2EHPA), 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC88A) and tributyl phosphate (TBP)), and the influences of experimental parameters such as extractant concentration, organic/aqueous phase ratio, diluent type, pH, extraction time and stripping agent concentration were examined. Results showed that light REEs (LREEs) and heavy REEs (HREEs) in the pregnant leach solution were selectively separated with D2EHPA via a two-stage extraction process. In the first-stage of solvent extraction, >90% of (0.05 g/L) HREEs was extracted with 1.8 M D2EHPA in kerosene while the vast majority (>95%) of LREEs was remained in raffinate. In the second-stage, >93% (1.01 g/L) of LREEs was extracted from the raffinate with 1.8 M D2EHPA dissolved in kerosene at pH 1.6. HREEs (>95%) and LREEs (>90%) loaded with D2EHPA after the first and second-stage of extraction were stripped by 4 M H 2 SO 4 and 1 M H 2 SO 4 solutions, respectively. Distribution of middle rare earth elements (MREEs) was discussed through the extraction processes in this study.
In this study, the various organic extractants, namely D2EHPA, PC-88A, TBP, TBPP, TOA, and TOPO, were examined to extract REEs from sulphuric acid leach liquor of apatite ore. Extraction parameters including extractants type, the concentration of extractant, organic to aqueous phase ratio, and contact time were investigated. Stripping experiments were conducted using different concentrations (0.5-4 M) of hydrochloric acid. Results showed that the overall extraction of REEs into the PC-88 extractant were ranged between 20 and 35%, while their extraction with other extractants did not exceed 20%. Interestingly, heavy rare earth elements (Tb, Dy, Er, and Y) were selectively extracted with D2EHPA when the light REEs extraction was lower than 5%.
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