Performance of (2-Ethylhexylamino)methyl Phosphonic Acid Mono-2-ethylhexyl Ester for Extraction and Separation of Rare Earth Nitrates

The performance of the extractant determines the effect and efficiency of rare earth extraction and separation. The extraction and separation of rare earths( III) in nitrate medium by an a-aminophosphonic acid extractant (2-ethylhexylamino)methyl phosphonic acid mono-2-ethylhexyl ester (HEHAMP) followed the positive sequence extraction, which was the same as that in sulfate and chloride medium. Some representative were employed to investigate the separation selectivity. The reaction mechanisms of the extraction of rare earths at pH<1.0 were speculated which followed a cation exchange mechanism with the extraction complex being deduced as Yb2(NO3)5(HA2)& BULL;(H2A2)2. Compared with sulfate and chloride solutions, HEHAMP had higher performance in the separation of heavy rare earths in nitrate medium. It was not affected by the changing temperature at lower aqueous acidity but was an exothermal reaction at relatively high acidity, which was different from those in sulfate and chloride medium. The loading capacity of 30% HEHAMP for ytterbium was 32.65 g/L (calculated by Yb2O3), and the loaded organic phase could be effectively stripped by hydrochloric acid.