Ammonium Paratungstate Preparation -- Neutralization Method
Ammonium paratungstate (APT) preparation is an important part of smelting tungsten, whether it is chemical precipitation method, ion exchange method or extraction method,they all have to go through the process of ammonium trioxide to produce qualified APT.
APT is an important tungsten intermediate products , the higher the purity the greater the value, so APT preparation process is also the further purification of tungsten.
Neutralization is one of the most commonly used manufacturing method of para-ammonium tungstate, and it's settlement with hydrochloric acid and (NH4) 2 wo4 solution, precipitation crystallization of ammonium paratungstate, and the energy consumption is small, crystallization speed is fast, easily to recovery the fine particle APT.
The neutralization method is carried out in a reaction tank with a liner rubber. Heating with hydrochloric acid and (NH4) 2WO4 solution, ammonium paratungstate crystallization, the reaction is:
12(NH4)2WO4+14HCl+4H2O==5(NH4)2O·12WO3·11H2O+14NH3Cl
Putting (NH4) 2WO4 liquid into the reaction tank, and heat the temperature according to the requirements of the granularity of APT, general particle in about 75 °C, coarse particle above 90 °C, the fine particles under 50 °C.Under the intense agitation, slowly add concentration about 10% - 20% of hydrochloric acid, neutralization to pH 7-7.5, stop adding hydrochloric acid, thermal mixing 0.5 hours,make the pH stable, stand for 8-10 hours, 90% to 95% of tungsten in the solution generated APT precipitation. To get the needle after washing with deionized water containing 11 crystallization water of crystallization of ammonium paratungstate.
Compared with the evaporation method, the neutralization method has the advantages of low energy consumption, fast crystallization and easy access to fine particles APT, but sometimes the grain size of the crystal is very fine, which is not conducive to filtration and washing, but also easy to bring impurities.the acid reagent corrosion equipment, the reagent consumption is large, virtually increases the environmental cost.
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