π-Backbonding-Enabled Selective Extraction of Mn2+ over Mg2+ Using a Novel Di-Neodecyl Ethanedione Monoxime

Solvent extraction is considered as an eco-friendly and efficient technology to extract manganese from an industrial leaching solution based on ores or post-consumer products. However, it is imperative to propose a novel extractant capable of independently and selectively extracting manganese ions from impurities since the separation efficiency of a single extractant is limited. We introduced a novel extractant di-neodecyl ethanedione monoxime (DEM) to extract manganese ions and conducted a comparative extraction analysis with neocapric acid (Versatic 10). The maximum extraction efficiencies of DEM and Versatic 10 separately achieved at 97.34% and 87.62%. And the selectivity tests for the extraction and separation of Mn 2+ and Mg 2+ suggested that DEM exhibited superior selectivity towards manganese ions than Versatic 10. FTIR spectrum analysis, saturation capacity experiments and mass spectrometry suggest that DEM can form a dual-ligand six-membered ring metal complex with manganese or magnesium ions through the formation of coordination bonds of N−O−M and C−O−M (M=Mn 2+ or Mg 2+ ). EDA-NOCV analysis illustrated that the π-backbonding between manganese atoms and extractant ligands contributes to the selectivity separation of manganese and magnesium ions. And the π-backbonding bond between the oxime group (–C=N–OH) and the manganese ion is stronger than that of the carbonyl group (–(C=O)–OH), confirming that DEM demonstrated superior selectivity compared to Versatic 10 in extracting manganese ions from magnesium ions.