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

Abstract

Herein, a series of α-hydroxyalkyl phosphinic acids were designed and first introduced in Mn2+ extraction and Mn2+-Mg2+ 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 Mn2+ and Mg2+, 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 PO 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 Mn2+ can be enriched from 11.2 g/L to 36.6 g/L, with Mg2+ decreased from 30.3 g/L to 0.6 g/L, which provides an efficient strategy for the preparation of high-purity manganese.