A novel phosphinic acid extractant and its application in the effective extraction of Mn2+ from Mn2+-Mg2+ sulfate solution

Herein, a series of α -hydroxyalkyl phosphinic acids were designed and first introduced in Mn 2+ extraction and Mn 2+ -Mg 2+ separation. The extraction tests indicate that the α -hydroxy-2-ethylhexyl phosphinic acid ( α -H-2-EHA) possesses superior extraction ability compared to di-2-ethylhexyl phosphinic acid (P204) for Mn 2+ and Mg 2+ , and the partition coefficient ( β ) is 28.2 at a saponification ratio of 30%. The results of quantum chemical calculation, FT-IR spectrum and slope analysis method reveal that the α -H-2-EHA can form stable four-membered ring structure with metal ions during the extraction process through P–OH and P O bonds. Furthermore, the HOMO composition results suggest that α -OH might also promote the interaction between extractant and metal ions. Finally, a three-stage countercurrent extraction—washing—stripping process was proposed and Mn 2+ can be enriched from 11.2 g/L to 36.6 g/L, with Mg 2+ decreased from 30.3 g/L to 0.6 g/L, which provides an efficient strategy for the preparation of high-purity manganese.