Synthesis of new extractant P113 for cerium(IV) extraction and higher separation over thorium from bastnaesite

Abstract

Cyanex923 (a mixture of four trialkyl (hexyl and octyl) phosphine oxides) has been extensively employed in the recovery of cerium (Ce(IV)) and fluorine (F), as well as the separation over thorium (Th(IV)) from bastnaesite. However, rigorous production conditions and involvement of highly toxic raw materials (PH3) have been critical problems to be solved during the synthesis of Cyanex923. Meanwhile, its extraction performance remains to be improved. Therefore, we attempted to adjust the feed ratio to increase the proportion of short carbon chain components, successfully synthesized a novel extractant (P113, a mixture of four trialkyl (hexyl and octyl) phosphine oxides) with contents of each component different from Cyanex923 using an environmentally benign method. The comparison with Cyanex923 revealed obvious improvement of P113 in terms of extraction efficiency, selectivity and saturation capacity. The extraction efficiency and saturation capacity of Ce(IV) were increased by 10% and 10 g L-1, respectively. Separation factor of Ce(IV)/Th(IV) was increased from 16 to 27 at 2 mol L-1 H2SO4. Furthermore, P113 presented excellent regenerability. The superiority of P113 was theoretically explored using the density functional theory (DFT) and polarizable continuum model (PCM), and the results indicated that THPO (trihexyl phosphine oxide) had lower extraction phase transfer energy than TOPO (trioctyl phosphine oxide) from aqueous phase to organic phase. The comprehensive evaluation of P113 demonstrated the feasibility employed in the recovery of Ce(IV)-F and the separation of Th(IV) from bastnaesite, which advanced industrial application of the novel extractant, and held significant value for the utilization of resources and environmental protection.