Further improvement for separation of heavy rare earths by mixtures of acidic organophosphorus extractants

Abstract

This work aims to improve the extraction performance of organophosphorus acid extractants (di-(2-ethylhexyl) phosphoric acid (P204), 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester (P507, H2A2), di-(2-ethylhexyl) phosphinic acid (P227, H2B2) and bis (2,4,4-trimethylpentyl) phosphinic acid (Cyanex272, C272)) for the extraction of heavy rare earths (HREs) from chloride medium by simple mixed two of them and formed six mixture systems. The comparison of extraction properties for lutetium (Lu) revealed that mixture of P507 and P227 is the most effective among the six mixed systems. Under the premise of no emulsification, this system also showed lower stripping acidity, higher load and shorter equilibrium time than others. Worthwhile, a synergistic effect was found by the mixture of P507 and P227 for Lu(III) extraction. A cation exchange mechanism was determined by slope analysis method. FT-IR was adopted to characterize the structure of extracted complex. The composition of extracted complex was determined as Lu(HB2)(HA2)2. In addition, this mixture system showed high separation ability of HREs. Its average separation factor of adjacent HREs from Ho to Lu was 2.19, superior to the single P507 (1.21) or P227 (1.83) system. More importantly, the mixture of P507 and P227 system has revealed industrial application values for the separation of HREs from mixed feed solution.