Synergistic extraction of heavy rare earths by mixture of α-aminophosphonic acid HEHAMP and HEHEHP

Synergistic extraction of heavy rare earths (REs) were investigated in chloride media by the mixture of (2-ethylhexylamino)methyl phosphonic acid mono-2-ethylhexyl ester (HEHAMP) and 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester (HEHEHP). The maximum synergistic enhancement coefficients (R) of Lu, Yb, Tm, Er, Y and Ho are 2.89, 2.76, 2.54, 2.14, 2.14 and 2.06, respectively, when the mole fraction XHEHAMP is 0.5. The synergistic separation factors of the heavy REs are obtained (βY/Ho = 1.31, βEr/Y = 1.61, βTm/Er = 1.78, βYb/Tm = 1.76, βLu/Yb = 1.20). The extracted complex is determined to be RE[H(EHAMP)2][H(EHEHP)2]2 by the slope analysis method. The loading capacities of the mixtures consisting of 15% HEHAMP and 15% HEHEHP for Y and Lu are about 26.59 g/L (Yb2O3) and 27.25 g/L (Lu2O3), respectively.