Mechanism of selectivity of tri-n-octylmethylammonium chloride for vanadium

Abstract

Ionic liquid (IL)-based extraction is a promising and environmentally benign separation technology. Processes for quaternary ammonium-based IL extraction of vanadium have been extensively studied, but the vanadium extraction mechanism has not been accurately confirmed. This study investigated vanadium extraction from sulphuric acid leachate of shale by solvent extraction with tri-n-octylmethylammonium chloride (TOMAC/CH₃NClR₃). The results indicated that 90.50 % of the vanadium extraction percentage comprised one stage under the optimal condition experiments. These experiments were carried out at pH 1.8; the IL phase consisted of 25 vol% TOMAC, 15 vol% TBP, and 60 vol% sulfonated kerosene; O/A phase ratio of 1:7.5; extraction time of 120 s. The forms of vanadium and impurities present were revealed by the solution chemistry, Medusa software simulation. The extraction mechanism of vanadium was investigated using ultraviolet spec-trophotometer (UV–Vis), fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (NMR), and hotometer matrix-assisted laser-resolved ionization time-of-flight mass spectra (MALDI-TOF-MS). Under extraction conditions at pH 1.8, vanadium was present as an anion in the form H₂V₁₀O4- 28 and HV₁₀O5- 28. Since the extraction mechanism of TOMAC was anion exchange, the extracted vanadium was mainly present as the anionic complex [(CH₃NR₃)₄·H₂V₁₀O4- 28]/[(CH₃NR₃)₅·HV₁₀O5- 28]. The ESP map of TOMAC and V (V) was calculated to confirm the reaction sites and was used to verify the anion exchange mechanism.