Extraction And Separation Of Chromium-Containing Vanadium Slag Leaching Solution With Pyridine Ionic Liquids

Vanadium and chromium are important strategic resources.Due to their similar nature,they usually exit in vanadium-titanium magnetite in a symbiotic manner.Chromium-containing vanadium slag is an important intermediate product produced in the process of the smelting of vanadium-titanium magnetite.It also can be used as an effective resource of vanadium and chromium.The most commonly used extraction method of vanadium and chromium in industry is roasting leaching.The separation and purification of vanadium and chromium from leaching solution have been one of difficult and attractive field.However,there are many problems in the conventional separation technologies.In contrast with other methods,solvent extraction method has more short process flow,is more easily operated and cost lower.Therefore,the solvent extraction method with large separation coefficient and friendly environment is adopted in this thesis.The traditional extractants remain severe pollution and poor extractant selectivity.Therefore,it is a profound significance to further explore and select new green extractants.Ionic liquids have shown potential application value in metal separation and extraction due to their excellent properties.High selectivity and efficiency of ionic liquids have attracted more attention.Hence,the application of ionic liquids as extractants in the separation of vanadium and chromium will bring new opportunities to solve problems of resource shortage and environmental pollution.In this thesis,the leaching solution of chromium-containing vanadium slag after sodium salt roasting and pyrometallurgy to extract iron that comes from Panzhihua-xichang of Sichuan province was used as the raw material.The study was designed to extract and separate V5+ and Cr6+ by solvent extraction using pyridine ionic liquids as extractants.The main contents of this thesis are as follows:(1)N-octylpyridinium hexafluorophosphate([OPy][PF6])has hydrophobic property and is not suitable for this study The extraction of V5+by N-octylpyridinium chloride([OPy]Cl)and N-octylpyridinium tetrafluoroborate([OPy][BF4])as extractants were investigated.The optimal conditions of extracting V5+ were as follows:n-pentanol was the optimal diluent,the mass concentration of[OPy]Cl and[OPy][BF4]were 50.0 g·L-1 and 55.0 g·L-1 respectively,the equilibrium time were 90 s and 105 s respectively,the temperature was 25℃,and the pH was 8.517.In these conditions,the extraction rate of V5+were 95.42%and 89.25%respectively.(2)The extraction of Cr6+ by N-octylpyridinium chloride([OPy]Cl)and N-octylpyridinium tetrafluoroborate([OPy][BF4])as extractants and n-pentanol as diluent were investigated.The optimal conditions of extracting Cr6+ were as follows:the mass concentration of[OPy]Cl and[OPy][BF4]were 20.0 g·L-1 and 25.0 g·L-1 respectively,the equilibrium time were 30 s and 45 s respectively,the temperature was 25℃,and the pH was 8.503.In these conditions,the extraction rate of Cr6+ were 70.01%and 55.85%respectively.(3)The higher initial concentration of metal ion was,the lower extraction rate was.Sodium chloride was not conducive to the extraction process of[OPy]Cl extracted V5+and Cr6+,while had almost no effect on the extraction process of[OPy][BF4]extracted V5+and Cr6+.while sodium sulfate was not conducive to the extraction process of Cr6+,while had almost no effect on the extraction process of V5+.(4)To investigate the extraction mechanism,iso-molar continuous variation method,saturating capacity method,slope method,ion selective electrode method,UV-vis and FT-IR were used.The extraction mechanism of V5+and Cr6+ by[OPy]Cl and[OPy][BF4]were determined that the proceed via anion exchange to extract.[OPy]+combined with HVO42-and CrO42-to be[OPy]2[HVO4]and[OPy]2[CrO4].(5)Furthermore,Cl-prefers to carry out ion exchange with HVO42-and CrO42-due to the size of anion volume and charge density of ionic liquids.Thus,[OPy]Cl has better extraction effect on V5+and Cr6+ than[OPy][BF4].(6)V5+and Cr6+ were stripped out from the loaded organic phase with ammonium chloride.The optimal conditions of stripping V5+and Cr6+ were as follows:The pH was 8.5,the molar concentration of ammonium chloride were 1.5 mol·L-1 and 0.3 mol·L-1 respectively,the stripping time were 30 min and 20 min respectively,the temperature was 25℃.In these conditions,the stripping rate of V5+and Cr6+ were 98.54%and 85.93%respectively.(7)The extraction and separation of chromium-containing vanadium slag leaching solution was studied.The process extraction-stripping-precipitation can separate V5+ and Cr6+effectively.Results of the experiments showed that the purity of V2O5 and Cr2O3 was high.The ionic liquid was regenerated by decompression distillation and combined with infrared spectroscopy analysis to confirm that the structure of the regenerated ionic liquid was consistent with the original ionic liquid.The regenerated ionic liquid was diluted with n-pentanol to prepare a new organic phase,and the extraction ability of the regenerated ionic liquid was determined.