Study On Efficiently And Selectively Extraction Of Vanadium From Vanadium Shale Acid Leaching Solution Using Tri-n-octylmethylammonium Chloride

In order to destroy the existence form of vanadium in the aluminosilicate mineral lattice and strengthen the release of vanadium from shale,the high-temperature and high-acid leaching system is currently used.Because of its low selectivity,impurity ions are also dissolved with the vanadium leaching,which makes the purification and enrichment of vanadium a necessary procedure.Solvent extraction is the most commonly used separation and enrichment method for vanadium extraction from vanadium shale,but traditional organic extractants have disadvantages such as long extraction stages and poor separation effect.Ionic liquids,as a kind of molten salts with low melting point（<100℃）,have the advantages of non-volatility,low melting point and excellent selective solubility,which provide new means and opportunities for solvent extraction technology.In this study,the multi-impurity leaching solution containing vanadium obtained from roasting-acid leaching of mica-type vanadium shale was studied,tri-n-octylmethylammonium chloride（TOMAC）was selected as extractant to investigate its extraction ability for vanadium and other major impurities in the leaching solution,to determine the optimum extraction and co-extraction process parameters,to explore the separation efficiency of vanadium and other major impurities during the extraction process and the reaction mechanism of extraction and synergistic stripping were analyzed..Firstly,the occurrence forms of vanadium and main impurity elements in acid leaching solution at different pH values were quantitatively calculated,and the differences of properties between impurity ions and vanadium ions provide guidance for subsequent purification and enrichment of vanadium.The optimum process parameters for efficiently and selectively extraction of vanadium from acid leaching solution by TOMAC were determined by the experiments:At 25°C,using TOMAC as the extractant,adjusting the pH of the acid leaching solution to 1.8,and using 20 vol%TOMAC,15 vol%sec-octanol,and 65 vol%sulfonated kerosene as the organic phase,extraction phase ratio（O/A）was1:10 and the extraction time was 2 minutes.After three stages countercurrent extraction,the total extraction percentage of vanadium was more than 99%;the synergistic strippant composed of 0.8 mol/L NaOH and 1.2 mol/L NaCl,the stripping ratio（O/A）is 2:1,and the stripping time is 10 min.After three stages countercurrent stripping,the concentration of vanadium was enriched from 1.74 g/L to 21.85 g/L,and the resulting vanadium-rich liquid can be used in the subsequent vanadium precipitation process.According to the results of the FT-IR analysis and the slope method,the composition of extraction by TOMAC is[CH₃NR₃]₄[H₂V₁₀O₂₈],and the extraction equilibrium constant K=275.867 is calculated by fitting.Through the FT-IR analysis and morphology comparison of the organic phase,the stripping mechanism of the NaOH-NaCl synergistic strippant system is the anion exchange mechanism of Cl^-and H₂V₁₀O₂₈^4-in the extraction complex.Therefore,the structure of TOMAC is restored in the process of stripping,the stripping and regeneration of the loaded organic phase could be carried out in one step.Moreover,the organic phase stripped by the NaOH-NaCl synergistic stripping system maintained a relatively high extraction efficiency（>90%）even across many cycles.