Sodium doped ammonium paratungstate (APT) is important raw material for manufacturing tungsten trioxide (WO3), and the content of sodium (Na) depends the particle size of tungsten powder. The APT with high sodium content will produce high sodium content of WO3 powder which is the upstream raw material for the manufacture of coarse particle tungsten powder; otherwise, the low content of APT will finally generate fine particle tungsten powder.
Coarse particle tungsten powder is the raw material of coarse grained cemented carbide, since the coarse grained cemented carbide has series advantages of good toughness, high hardness and thermal conductivity, excellent red hardness, and thus has been widely used in the fields of mining tool, stamping die, oil drilling, hard facing materials ect.. The main process for producing coarse grained cemented carbide is adding alkali metal in APT or tungsten trioxide, and getting coarse particle tungsten powder after carried out hydrogen reduction, then generating coarse particle WC powder after carbonization under high temperature, finally getting coarse grained cemented carbide after carrying out processes of wet milling, forming and sintering.
At present, the common producing method of sodium doped ammonium paratungstate is mechanical blending method, which is adding a certain amount of sodium salt into APT or tungstic acid and then getting mechanical blending with mixing equipment. In addition, an invention has pointed out a new method for producing ammonium paratungstate containing with high sodium, the steps are like bellow:
1. Decomposing tungsten concentrate with alkali solution and then going on with ion exchange, molybdenum removal and other process to generate ammonium tungstate solution;
2. Adding a certain amount of sodium salt according to the requirement of the subsequent product before evaporation crystallization to obtain sodium doped ammonium tungstate solution;
3. Carrying out evaporation crystallization until the end point of crystallization, stopping heating and cooling the solution to 20~50°C, filtering and draining the feed liquid to generate wet APT, then dry them to get dried high sodium doped ammonium paratungstate.