Methods to Produce Ammonium Paratungstate
Methods of producing ammonium paratungstate as follows:
(1) Neutralize:Mixed HCL(aq) with (NH4)2WO4(aq) under homoeothermy,and ammonium paratungstate bacame.The shortage of neutralize is crystal size to small to filtration and washing,the productin contains a large number of Cl- in solution which will corrade equipments,brings more impurities, and low metal tungsten recovering.
(2) Evaporation method:Crystals precipitated by heating the ammonium tungstate solution.In spide of the disadvantage that taking long time to evaporation,energy consumption,long production cycle,it's widely used because of easy operating.
(3) Ion exchange method: It's widely used by foreign manufacturers,because of easy operating,sample equipment,less investment.
(4) The extraction method.
(5) Combination and evaporation legitimate.
(6) The freeze-drying method:Put a volume ratio of ammonium tungstate solution and liquid nitrogen (1: 2-3) into enamel plate, a little stirring,immediately injecte the solution mash with enamel plate into dried equipment.White crystals of ammonium paratungstate will come into being by compeletly water removed in the state of vacuum.If you need higher purity of ammonium paratungstate, electrolytic preparation and recrystallization method are supposed to be used.Besides,Japanese has a patent to higher the purity of ammonium paratungstate.
There will be different tungsten concentrate according to varieties of tungsten concentrate as follows:
1.Wolframite high pressure alkali cooking (caustic soda) - ion exchange - evaporative crystallization method;
2.Wolframite high pressure alkali cooking (caustic soda) - solvent extraction - evaporation crystallization;
3.Scheelite Su pressure cook - ion exchange - evaporative crystallization method;
4.Scheelite Su pressure cook - solvent extraction - evaporation crystallization;
5.Scheelite concentrate caustic soda fluoride Autoclave - ion exchange - evaporative crystallization method;
6.Scheelite concentrate caustic soda fluoride Autoclave - solvent extraction - evaporation crystallization;
7.Scheelite hydrochloric acid decomposition - ammonia dissolution - evaporative crystallization method.
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