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 (PH 3 ) 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 H 2 SO 4 . 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.
Shuang Sun,Yuefeng Deng,Ji Chen,Dan Zou,Yaxing Han,Mingyang Liu
Lithium has become increasingly important because of its irreplaceable role in lithium-ion batteries. Addressing the complex process and high energy consumption of the current adsorption-membrane integrated process for lithium extraction from high Mg/Li ratio salt lake brine, this study put forward an integrated process of adsorption-solvent extraction. Taking the desorption solution of adsorption method as raw material, the process parameters and extraction mechanism of lithium by the novel extraction system were investigated. A novel process of lithium recovery from the desorption solutions of salt lakes by solvent extraction was proposed for the first time. The composition of the extraction system was studied and determined to be HTTA-P113-kerosene. Compared with the previously reported neutral ligands (TOPO, Cyanex923), P113 not only exhibited excellent synergistic extraction ability but also had good miscibility and a green synthesis process. The effects of saponification degree, extraction time, temperature and phase ratio on lithium extraction and β Li/Na were systematically investigated. Through the four-stage countercurrent extraction, more than 99.2 % of lithium could be extracted by the organic phase consisting of 0.4 mol L −1 HTTA, 0.4 mol L −1 P113, saponification degree of 80 % at O/A ratio of 1:1 and equilibrium pH of 6.78. Furthermore, after the scrubbing and stripping process, the lithium-rich solution containing 21.64 g L −1 Li + and 0.037 g L −1 Na + was obtained. The Li 2 CO 3 products with a purity of 99.5 % were successfully prepared from the lithium-rich solution by precipitation method. Finally, the extraction mechanism was studied via the slope analysis method and FT-IR spectra. It was indicated that the extracted lithium species were Li(TTA)(P113).
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