Ion exchange method is a technology earlier used in the industry,the chemical composition of ammonium tungstate solution meets the requirements of evaporation,and the crystallization of ammonium paratungstate has a  high purity.Besides,ion exchange method has shorter industrial process,simple equipment, less investment and other advantages,many foreign manufacturers use it to produce ammonium tungstate solution.

Tungsten ion exchange process is divided into four steps as follows:the adsorption,the column loading washing,desorption, the column was washed four load process.In the solution of tungsten concentrate leaching by austic soda,tungsten appears in NA₂WO₄,phosphorus, arsenic, silicon, respectively,were exist in forms of  PO₄^3-.AsO₄^3- , SIO₃² .

Since tungstate has greater affinity with strong base anion resin than phosphorus, arsenic, silicon ions,therefore,it has a higher adsorption selectivity.First,we adsorpt tungstate form sodium tungstate with the ion exchange resin solution,so that P, Mo, As and Si remaining in the liquid and drained away.And then desorbe tungsten from the resin by NH₄Cl and NH₃.H₂O or NACl solution.Adsorption, desorption process as follows:
2RCl(s)+NA₂WO4(aq)→R₂WO₄(s)+2NACl(aq)
R₂WO₄(s+2NH₄Claq)→2RCl(s)+(NH₄)₂WO₄(aq)
Through the above adsorption and desorption process,impurities are removed from the solution,so we get high purity (NH4)2WO4 liquid.China is now using a strong base anion called W.AMacroporous resin ion. W.A has a higher capacity in separating tungsten, molybdenum, phosphorus, arsenic, silicon in sodium tungstate solution from sodium tungstate solution than strongly basic,and has a better effect in removing aluminum.W.A has been widely used in tungsten industry.

For evaporation method produce ammonium paratungstate,please see in http://m.forward-rubber.com/Culturecar/2015/140295.html.

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