Method two:Residual alkali decomposition 

Literature of<Research and practice of WO3 industrial method of ammonium paratungstate mother liquor recovery lime precipitation> pointed out that WO3 mainly appears in the form of tungstate or ammonium paratungstate,and accompany a few heteropoly acid salt and a large number of Mo and other impurities.The method of residual alkali decomposition  using coarse sodium tungstate in the residual alkali(alkali containing about 30~40g/L) reacte with tungsten and ammonium molybdate in mother liquor,reaction equation as follows:

2NaOH+(NH4)2WO4→Na2WO4+2NH4OH 

2NaOH+(NH4)2MoO4→Na2MoO4+2NH4OH
 

Adding 5 times of theoretical amount of Na2S into the solution we obtained after response,Mo precipitation sinking in the form of 

MoS3 in acidic(pH =2.5~3.0) environment,after filtration,solution return to main flow to combine with sodium tungstate for impurity 

removal, reserving for subsequent machining, mainly process shown in figure:

 

The mother liquor that dealing by alkali decomposition method combined with sodium tungstate will show an obvious effect. Also,it does no harm to the whole processing,and the APT it producing meets the requirement of high purity.

For Recycling and Reusing Ammonium Paratungstate Crystal Liquor 1/3,please see in 
http://news.chinatungsten.com/en/tungsten-information/81754-ti-10570