CO2 direct crystallization method to prepare ammonium paratungstate (APT) is introducing carbon dioxide (CO2) gas into the solution, to form the reaction system of CO2 - sodium tungstate – ammonia, and further directly crystallize to get ammonium paratungstate, and generate the sodium carbonate at the same time, like the following steps:
1. Add ammonia gas or ammonium salt or the aqueous solution of both into sodium tungstate solution according to a certain percentage to get sodium tungstate – ammonia solution;
2. Inlet the carbon dioxide with a certain pressure into the sodium tungstate – ammonia solution and carry out insulation under 20~100°C for 1~72 hours to generate serous containing with crude ammonium paratungstate crystal;
3. Take out a solid-liquid separation to the serous, and the filtrate is returning to decomposition process of tungsten concentrate;
4. The solid generated from step 3 is firstly washed with ammonium salt solution under 20~100°C, and secondly washed with clear water to get APT.
Compared to other method, this process of CO2 direct crystallization method preparing ammonium paratungstate is combining alkali neutralization and APT crystallization in one step, has the advantages of sample process, low energy consumption and cost and others; at the same time, the generated of sodium carbonate can use for decompose tungsten ore which realize the alkali circulation of reaction system, and reduce the environment pollution during the tungsten metallurgy process.