| In view of the nature of metatungstate and the characteristics of bipolar membrane electrodialysis, a novel technology of preparing metatungstate with high efficiency and environmental friendliness was proposed. The research covers preparing ammonium metatungstate solution from industrial ammonium tungstate solution by bipolar membrane electrodialysis, preparing AMT of solid from the ammonium metatungstate solution by alcohol crystallization, spray drying and cooling crystallization respectively, preparing sodium metatungstate concentrated solution from sodium tungstate solution by bipolar membrane electrodialysis——evaporation. The main experimental results are as follows:A feasible experiment of preparing ammonium metatungstate solution by bipolar membrane electrodialysis was studied, the results indicate that industrial ammonium tungstate solution can be successfully converted into ammonium metatungstate solution by bipolar membrane electrodialysis; the advantages of this process are short flow, process stability and simple operation. Current efficiency can reach above70%, DC consumption of0.0795kWh/mol [NH3] and871.6kWh/T [WO3], WO3yield more than99.9%.The effects of current density, WO3concentration of salt compartment solution, NH4HCO3initial concentration of base compartment solution, and solution temperature and pH value of salt compartment solution on current efficiency and DC consumption ware studied. The optimal operating conditions for bipolar membrane electrodialysis were WO3concentration range of salt compartment solution of150-200g/L and initial NH4HCO3concentration of1.5mol/L at31℃and adding a certain concentration of NH4HCO3solution to the base compartment of continuous limits free NH3·H2O formation and pH of2.8with higher current density(above650A/m2)A long time and continuous comprehensive experiment of preparation of ammonium metatungstate solution with the optimal operating conditions has been conducted, a higher current efficiency and low DC power consumption (current efficiency70%, DC power consumption of0.0743kWh/mol [NH3] and825.5kWh/T [WO3]) ware obtained. The production process without pollution, environmental friendliness, it has promising in industrial application.Aging experiment of ammonium metatungstate solution prepared by bipolar membrane electrodialysis has been conducted, The determined aging conditions ware the pH value range of ammonium metatungstate solution before aging of2.70-2.90and keep at90℃under the condition of volume conservation for48hours. On this basis, AMT of solid was prepared using alcohol crystallization, and The optimal operating conditions of alcohol crystallization were ammonium metatungstate solution after aging is concentrated to the WO3concentration is higher than1350g/L, adding3times the volume of concentrated liquid of absolute alcohol, crystallization time for20min with stirring, and the crystal cold drying for2hours. The process of crystallization rate of greater than95%, AMT crystal prepared was white crystal and the CWO3purity of product reached86%with water solubility of AMT above300g/100g H2O at20℃. The AMT product which meets the Chinese national standard can be directly used to prepare catalysts containing tungsten.AMT of solid was prepared using spray drying and cooling crystallization respectively. The product prepared by spray drying was fine powder similar to white and the CWO3purity of product was94.39%, yield near to100%; The product prepared by cooling crystallization was blue-grey crystal and the CWO3purity of product was84.58%. Both of the AMT water solubility above300g/100g H2O at20℃.A feasible experiment of preparing sodium metatungstate solution by bipolar membrane electrodialysis was studied; the results indicate that self-made sodium tungstate solution can be successfully converted into sodium metatungstate solution by bipolar membrane electrodialysis. The advantages of this process are short flow, process stability and environmental friendliness. Current efficiency can reach above75%, DC consumption of0.0630kWh/mol [Na] and591.3kWh/T [WO3], WO3yield more than99.9%.Aging experiment of sodium metatungstate solution prepared by bipolar membrane electrodialysis has been conducted, The determined aging conditions ware the pH value range of ammonium metatungstate solution before aging of3.30-3.40and keep at90℃under the condition of volume conservation for48hours. On this basis, sodium metatungstate concentrated solution was prepared using evaporation. The sodium metatungstate concentrated filtrate was clear and colorless liquid for pH3.44-3.63and the specific gravity of about2.88g/cm3. It has good stability at20℃in avoid light and sealing conditions and properties near to the imported products sold in the market. |
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