Enhancing separation of cerium(IV) and thorium(IV) from sulfate medium by introducing cyclohexyl group into molecule of an aminophosphorus extractant

Enlarging the steric hindrance to the molecular structures of extractants is a common way to improve their selectivity. To improve the separation factor of thorium(IV) and cerium(IV), cyclic groups having large steric hindrance such as phenyl, cyclohexyl, and benzyl were introduced into the α -aminophosphonate extractant molecules. Bis(2-ethylhexyl) ((phenylamino)methyl) phosphonate (PAMP), bis(2-ethylhexyl) ((cyclohexylamino)methyl) phosphonate (CAMP), and bis(2-ethylhexyl) ((benzylamine)methyl) phosphate (BAMP) were synthesized and applied in the separation and recovery of thorium(IV) and cerium(IV) from sulfuric acid solution. The separation ability between cerium(IV) and thorium(IV) descends in the order of CAMP > BAMP ≈ Cextrant230 > DEHAMP >> PAMP, which is consistent with the decreasing order of steric hindrance. Nearly non-extraction of both cerium(IV) and thorium(IV) and the lowest separation ability for PAMP will be due to the conjugation of the lone pair of the amino N atom and benzene ring in PAMP. Furthermore, the extraction of REs(Ⅲ) by CAMP is lower than that of thorium(IV). Thermodynamic parameters ( ΔG 0 , ΔH 0 , ΔS 0 ) and extraction equilibrium constants were determined. An extraction process was developed to separate and retrieve thorium(IV) and cerium(IV) from a bastnaesite leaching solution. The final product purity of CeO 2 and ThO 2 is 99% and 98.4%, respectively, and the yields are 90.2% and 97.6%, respectively.