Hexamethylene tetramine method to produce ammonium paratungstate (APT) is a way which not only can enhance the recovery rate of ammonium paratungstate, but also can recover the remaining tungsten from ammonium tungstate solution without returning. Generate precipitate of tungsten compound and hexamethylene tetramine by adding hexamethylene tetramine into ammonium tungstate solution, then decompose the precipitate with ammonia water to get the secondary ammonium tungstate solution, finally precipitate out APT crystal by heating. Its production process is:
1. Add hexamethylene tetramine into the maiden ammonium tungstate solution, wherein the mole ratio of hexamethylene tetramine: tungsten is 0.5 ~ 1.0, then adjust the pH value to 1.5 ~ 1.5 by sulfuric acid, control the liquid temperature within the 20°C, to get high concentrate of maiden precipitation containing with tungsten and hexamethylene tetramine;
2. Separate the maiden precipitation containing with tungsten and hexamethylene tetramine sediment with maiden mother liquid by methods of filtering or decanted;
3. Dissolve the maiden precipitation in ammonia water to get the secondary sodium tungstate solution containing with hexamethylene tetramine;
4. Heat the secondary ammonium tungstate solution to 90 ~ 100°C until the solution volume is concentrated to about 25% of the original volume, thus to generate high purity secondary precipitation of ammonium paratungstate, while all the hexamethylene tetramine is persist in the secondary mother liquor.
Studies have found that this kind of hexamethylene tetramine method producing ammonium paratungstate can recover about 95% of the tungsten; meanwhile, by adjusting pH value, the residual tungsten in the mother liquid can be completely precipitated; In addition, this method does not introduce impurities, and can obtain high purity APT crystal.