Lithium recovery from Li3PO4 leaching liquor: Solvent extraction mechanism of saponified D2EHPA system

Recovery of low-concentration lithium resources by Li3PO4 precipitation is an effective method and using saponified D2EHPA-kerosene is a promising method for the treatment of Li3PO4. In this paper, the effects of additives on the extraction of lithium from Li3PO4 leaching liquor and the mechanism of lithium extraction by saponified D2EHPA were investigated. The results showed that the addition of tributyl phosphate (TBP) could promote lithium stripping. Experiments confirmed that lithium in solution could be extracted by one-to-one cation exchange with sodium in the organic phase. Slope analysis showed that LiR·NaR was formed when lithium was extracted by saponified D2EHPA, and LiR·NaR·0.1TBP was formed when adding TBP (R is D2EHPA anion). Infrared spectroscopy indicated that the addition of TBP or the saponification of the organic phase depolymerized the D2EHPA dimer. Adding TBP improved lithium's stripping ratio and the concentration of lithium in the stripping solution, which are favorable to the subsequent Li2CO3 precipitation process. This paper provides a deeper understanding of the conversion of lithium phosphate to lithium carbonate using a saponified D2EHPA system.