Extraction and stripping of rare earths using mixtures of acidic phosphorus-based reagents

Studies were carried out on the extraction characters of trivalent rare earths from chloride solutions using organophosphorus acids 2-ethylhexylphosphonic acid mono-(2-ethylhexyl) ester (HEHEHP) combined with [di-(2-ethylhexyl)-phosphoric acid (HDEHP), isopropylphosphonic acid 1-hexyl-4-ethyloctyl ester (HHEOIPP), bis(2,4,4-trimethylpentyl)-phosphinic acid (Cyanex 272), bis(2,4,4-trimethypentyl)-monothiophosphinic acid (Cyanex 302) or bis(2,4,4-trimethypentyl)-dithiophosphinic acid (Cyanex 301)] as extractants. The effect of the equilibrium aqueous acidity on the extraction was studied. According to the corresponding separation factors for adjacent pairs of rare earths, it could be concluded that HEHEHP and Cyanex 272 could be employed for the separation of Tm(III), Yb(III), Lu(III) from the other rare earths. Taking Yb(III) as an example, based on the different stripping acid, the potential of the stripping was estimated.