Zinc Tungstate by Cationic Membrane Electrolysis Preparation

Zinc tungstate (ZnWO₄) with wolframite structure is an important inorganic material. Because of its excellent chemical stability, high refractive index, high X-ray absorption coefficient, high quantum yield and good photoelectric activity, it is used in X^-, gamma-ray scintillators, photoluminescence, microwave systems, solid-state lasers, gas and humidity sensors, photocatalysis, acoustooptic fibers and magnetism. Materials and other fields have a wide range of applications.

In the aspect of ZnWO₄ synthesis, more applications include sol-gel method, solid-state synthesis, molten salt method, mechanochemical synthesis method, ultrasonic method, solvothermal method, hydrothermal method and so on. However, due to the homogeneous mixing of raw materials, there are many metal oxide impurities in solid-state synthesis. The disadvantages of sol gel method, aqueous phase precipitation method, hydrothermal method and microwave method are the existence of additives or the longer reaction time.

In order to solve the problems of long reaction time and many impurities in the preparation of zinc tungstate, some researchers used cationic membrane electrolysis to prepare zinc tungstate. This method has the advantages of short reaction time and high purity of the product. The scheme process includes:

(1)Using zinc sheet as anode, inert electrode as cathode, sodium tungstate solution with 95 mL concentration of 0.01 mol/L as anode solution, 90 mL alkali solution as cathode solution, and cation membrane as separator in a two-chamber electrolytic cell, constant voltage electrolysis of sodium tungstate solution was carried out at room temperature to 50 ℃ for 10 minutes, that is, Na⁺ ions were all transferred to the cathode chamber.

(2)After the electrolysis is completed, the product obtained on the anode is filtered while being washed with deionized water to clean Na+ and the additive ions, and the filtered filter cake is controlled to a temperature of 60 °C for 2 h, and dried. The temperature is raised to 500 °C at a heating rate of 2.5 °C / min in an air atmosphere for high-temperature calcination for 1 h, and after cooling, it is naturally cooled to room temperature to obtain pure zinc tungstate.

After determination, only three elements of zinc, W and O were found in the product, which indicated that zinc tungstate prepared by cationic membrane electrolysis method was pure phase, without impurities, and zinc tungstate could be prepared by one step electrolysis. Therefore, the preparation process was simple, easy to operate, low investment and large amount of synthesis, which could be directly applied to industrial production.

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