Selective Extraction and Separation of Ce (IV) and Th (IV) from RE(III) in Sulfate Medium using Di(2-ethylhexyl)-N-heptylaminomethylphosphonate

The extraction and separation of Ce(IV) and Th(IV) from trivalent rare earths (RE, including scandium) in sulfate medium using di(2-ethylhexyl)-N-heptylaminomethylphosphonate (DEHAMP, L) were studied. The effects of H2SO4 concentration, extractant concentration, and temperature on the metal extraction were investigated systematically. It was found that the extraction of metal ions by DEHAMP decreases in the following order: Ce(IV) > Th(IV) > Sc(III) > other RE(III). A possible extraction mechanism was proposed and the extracted complexes as Ce(SO4)(2)2L and Th(HSO4)(2)SO4<bold>L were determined by the slope analysis method</bold>. Thermodynamic parameters (H, G, and S) were calculated. The extraction reactions of Ce(IV) and Th(IV) were each exothermic processes. The loaded Ce(IV) and Th(IV) can be stripped efficiently by 3% H2O2 and 4 mol/L HCl, respectively. The extraction capacity of 0.63 mol/L DEHAMP is 30.0 g/L CeO2 and 24.4 g/L ThO2, respectively. Furthermore, a solvent extraction process to selectively extract and recover cerium and thorium from bastnaesite leaching was proposed, by which the purities of cerium and thorium products reached 97.2% and 96.5% with a yield of 85.4% and 98.8%, respectively.