Effluent derived from spent lithium-ion batteries (LIBs) electrolyte or discarded ionic liquids (ILs) is a potentially resource of hexafluorophosphate (PF) which can be recovered through solvent extraction. In this study, an efficient extraction approach was proposed to recover the hexafluorophosphate from solutions. A basic investigation on the interactions between extractants and hexafluorophosphate was firstly carried out using density functional theory (DFT), which demonstrated the stability of the extracted complex structure. The effects of extractant (Alamine336) and modifier, common anions and metallic ions in waste-streams, initial pH, and temperature on the extraction efficiency were explored. The results showed that 96.16 % of hexafluorophosphate could be extracted and transferred into organic phase using Alamine336/modifier as extractant under optimal conditions (0.15 mol/L of Alamine336 and 0.25 mol/L of modifier). The organic phase exhibited an excellent extraction capability of >95 % under optimal condition. Moreover, it was found that the use of sodium hydroxide as stripping reagent presented a superb stripping and cycling properties. Thermodynamic analysis and spectral data indicated that PF was extracted into the organic phase in the form of RNH⋅PF, which is a spontaneous exothermic process. The novel extraction method provides a broad application perspective for the removal and recovery of valuable hexafluorophosphate from aqueous system.

中文翻译：

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从废水中分离六氟磷酸盐的绿色创新方法


来自废锂离子电池（LIB）电解质或废弃离子液体（IL）的废水是六氟磷酸盐（PF）的潜在资源，可以通过溶剂萃取进行回收。在这项研究中，提出了一种有效的萃取方法来从溶液中回收六氟磷酸盐。首先利用密度泛函理论（DFT）对萃取剂和六氟磷酸盐之间的相互作用进行了基础研究，证明了萃取的络合物结构的稳定性。探讨了萃取剂 (Alamine336) 和改性剂、废物流中的常见阴离子和金属离子、初始 pH 值和温度对萃取效率的影响。结果表明，在最佳条件下（Alamine336/改性剂0.15 mol/L，改性剂0.25 mol/L），96.16%的六氟磷酸盐可以被萃取并转移到有机相中。在最佳条件下，有机相表现出>95%的优异萃取能力。此外，发现使用氢氧化钠作为剥离剂呈现出极好的剥离和循环性能。热力学分析和光谱数据表明PF以RNH·PF的形式被萃取到有机相中，这是一个自发的放热过程。这种新颖的萃取方法为从水系统中去除和回收有价值的六氟磷酸盐提供了广阔的应用前景。