The quality of ammonium paratungstate(APT) directly affects the quality of tungsten product,each impurity content in ammonium paratungstate crystalline powder should not exceed 2*10-5 during the production of doped tungsten wire and tungsten alloy wire.People use method of recrystallization to produce high purity ammonium paratungstate.
 

Way of using APT(aq) to producing high purity ammonium paratungstate in China like this:Dissociation ammonium paratungstate with a certain temperture→dissolve in ammonia→clarify→filter→ammonium tungstate(aq)→evaporation and crystallization→washing→drying→high purity ammonium paratungstate.

 

In America,the method is something different.A certain proportion of mmonium paratungstate completely dissolves in ammonia(4.9%) under the tempreture of 120℃,keep the status for 2 hours. Continue boiling the solution until 81% tungsten crystals have been separate out,analysis the sample,mainwhile,filtering the solution.Then get the crystal dissolved in ammonia,repeat it until you get 81% tungsten crystals separated out again.So，the purity of ammonium paratungstate will be obviously improved.