Ammonium paratungstate (APT) is an intermediate product from tungsten smelting process, and it is mainly used to produce blue tungsten and tungsten trioxide which are raw materials of the cemented carbide powder production. In the ammonium paratungstate (APT) production of ion exchange process, if control is not good, levels of calcium in the products are easy to exceed , that is high-calcium-contented ammonium paratungstate.

High-calcium-contented calcium ammonium paratungstate have influence on the products manufacture. On the one hand, it ultimately affects the quality of cemented carbide, giving users economic losses, on the other hand, the product manufacturer can not only achieve good economic efficiency because products accumulated , but also resulting in a waste of valuable resources of tungsten to some extent, it must be re-treated. Some manufacturers produce some serious Ca-content-failure of ammonium paratungstate. If treat these unqualified products by the traditional process, there is a long process line, high consumption, and high cost.