New Process of Preparing High Purity Molybdic Acid from Crude Sodium Molybdate Solution
High-purity molybdate products were prepared from crude sodium molybdate solution by purification-bipo-lar membrane electrodialysis-crystallization method.The effects of key parameters of ion exchange on the adsorption capacity of calcium and magnesium ions in the purification process,the effects of initial molybdenum concentration and current density in sodium molybdate solution on power consumption in the process of bipolar membrane electro-dialysis,and the effects of crystallization time on the purity of molybdic acid were investigated.The results showed that the optimum operating parameters for crude sodium molybdate solution to reach the concentration of Ca and Mg ions both<0.3 mg/L by ion exchange were pH 9～10 of sodium molybdate solution before adsorption,and the flow rate of adsorption solution was 8～16 m/h.The more optimum process parameters for bipolar membrane electrodial-ysis were Mo concentration of sodium molybdate solution in the salt chamber was 80～100 g/L,the current density was 300～400 A/m2,and the Mo yield was greater than 99.97%,K residual concentration was 3.7 mg/L,and Na residual concentration was86.4 mg/L;the average current efficiency was about 67.8%,and the DC power con-sumption was 925 kWh/T[Mo].The molybdic acid product obtained by evaporating the molybdic acid solution for 180 min had a more uniform particle size,high purity,and solubility,etc.,in accordance with the standards for raw materials in the catalyst industry.
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