| Bauxite containing varying degrees of V2O5, which can be used as the resources of vanadium extraction, and vanadium in alumina production processes have a great impact on the quality of the alumina products. In view of the harm of vanadium in alumina production processes and the existing recycling processes such as crystallization method and ion exchange method with the problems of long process, high energy consumption, low recycling rate, this paper put forward a new process which including the material liquid without treatment, the direct solvent extraction of vanadium from high alkaline solution of alumina spent liquor using quaternary ammonium salt as extractant and raffinate directly returned to the leaching process. In this paper, solvent extraction of vanadium from high alkaline solution with the modified quaternary ammonium salt was studied. And it was mainly investigated separately from the screening and transformation of extractants, the influence factors of extraction and stripping and the mechanism of extraction vanadium. It could be some reference value on the solvent extraction of the vanadium from alumina production process.Various types extractants were used in the extraction vanadium from high alkaline solutions and the results showed that the extraction performance of CO32- type quaternary ammonium salt TOMAC was significantly better than the HCO3-, SO42- and Cl- type quaternary ammonium salt TOMAC, so the CO32- type quaternary ammonium salt TOMAC was determined as extractant. Study on the transformation processes of Cl" type quaternary ammonium salt TOMAC were carried out. The times required for each step in the transformation process were identified by determining the concentration of Cl", SO42-, CO32-anion exchange in treated solution to calculate the exchange equilibrium rate and analysing the infrared spectra of extractants around the transformation process. Experimental results showed that under the condition of 2/1 for the organic phase ratio(O/A),25? for the temperature,1 hour for shaking time, SO42- type quaternary ammonium salt could be obtained after the Cl- type quaternary ammonium salt treating by 3mol/L for sulfuric acid for 7 times, then through washing the organic phase by 2mol/L for sodium hydrate for 2 times and treating by 1mol/L for sodium hydrogen carbonate for 5 times, the HCO3- type quaternary ammonium salt could be slao obtained, finally, after 2 times by 2mol/L for sodium hydrate, the CO32- type quaternary ammonium salt was obtained.The effects of extractant concentration, DL-2-Octanol concentration, alkaline and vanadium concentration of feed, phase ratio, oscillation time and temperature on the extraction of vanadium were investigated. The extraction isotherm curve of vanadium was also plotted. And the optimal extraction conditions were ascertained through the orthogonal experiment. Experimental results show that the single stage extraction rate of vanadium can reach 80% and the saturated loading capacity for V2O5 can reach 5.85g/L under the optimal conditions of alkaline of 1.5mol/L, vanadium concentration of 3.57g/L, phase ratio (O/A) of 2/1, temperature of 25?, oscillation time of 10 minutes, and the organic phase consists of 50wt% Trioctadecyl Methyl Ammonium Chloride (CO32-type)+20wt%DL-2-Octanol+30wt% sulfonated kerosene. After five stages counter-current extraction test, the extraction rate of vanadium reached 99.5% and the concentration of V2O5 leaving in the raffinate was less than 0.05g/L. By comparing the different stripping systems, the stripping agent composition was ascertained as 1.5mol/L Na2CO3 and 1.0mol/L NaOH. The single stage stripping rate of vanadium can reach around 75% under the conditions of phase ratio (O/A) of 1:1, temperature of 25? and oscillation time of 10 minutes. And the stripping isotherm curve of vanadium was also plotted. The results showed that the concentration of 4.2g/L for the loaded organic phase can be reduced to below 0.02g/L after two stages counter-current stripping test.The mechanism of vanadium extraction from high alkaline solution with quaternary ammonium salt extractant TOMAC was also studied in this paper. The results of the slop method, the saturation method and the molar method indicated that the mechanism of extractant extracting vanadium from high alkaline solution was anion exchange reaction, the composition forms of the extracted complex was proposed as (R3CH3N)3VO4, and the reaction equation was expressed as: 2VO43-+[(R3CH3N)2CO3]3(o)=2(R3CH3N)3VO4+3CO32-The thermodynamic analysis showed that the enthalpy ?H was -17.79kJ/mol when the quaternary ammonium salt TOMAC was used to extract the vanadium in the high alkaline solutions. The extraction of the vanadium was a heat process and it was disadvantage on the extraction of the vanadium when the temperature raised. The extraction dynamics results showed that the stirring strength and the interface contacting area had an effect on the extraction of vanadium. The extraction of vanadium in the alkaline solutions was hybrid control type. |
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