Also a kind of inorganic metal tungsten compound, ammonium paratungstate and ammonium metatungstate have certain differences in performance, production technology and application. First, the former is insoluble in water, the latter is easily soluble in water, and the aqueous solution is quite stable; Second, the former is the main raw material for the production of the latter; Third, the former is mainly used to produce tungsten products, the latter can be used to produce tungsten products, but also can be used as nuclear shielding material, corrosion inhibitor, petroleum catalyst. The following is mainly about the basic information of the former. Ammonium paratungstate is a white crystalline powder, Ammonium paratungState (” APT “), with the formula (NH4)10W12O41·5H2O, in sheet and needle forms. Its relative density is 2.3g/cm³, and the solubility of water is less than 2% at 20℃. The aqueous solution is weakly acidic and insoluble in ethanol, and its chemical stability is general. In addition to decomposition under acidic and alkaline conditions, it also reacts with hydrogen peroxide to form soluble peroxytungstate
In addition, it is worth noting that APT is easy to dehydrate and decompose under heated environment. Under conventional conditions, the thermal decomposition process can be divided into four stages: removal of water of crystal, decomposition into amorphous ammonia-tungsten bronze, transformation into ammonia-tungsten bronze and decomposition into tungsten trioxide. Experimental results show that when heated in air, APT begins to remove part of ammonia molecules when the temperature is below 100℃, while when heated strongly, APT removes all ammonia molecules and crystal water, and then turns into yellow tungsten oxide powder.
According to the different types of tungsten concentrate and impurities, APT production process can be divided into the following :(1) high pressure alkali boiling (sodium hydroxide solution) of wolfrite concentrate – ion exchange – evaporation crystallization method; (2) High pressure alkali boiling (sodium hydroxide solution) -solvent extraction-evaporation crystallization method of wolfrite concentrate; (3) soda pressure boiling – ion exchange – evaporation crystallization method for scheelite concentrate; (4) soda pressure boiling – solvent extraction – evaporation crystallization method for scheelite concentrate; (5) Caustic soda fluoride pressure boiling – ion exchange – evaporation crystallization method for scheelite concentrate; (6) Pressure boiling with caustic soda and fluoride – solvent extraction-evaporation crystallization method for scheelite concentrate; (7) Hydrochloric acid decomposition – ammonia solution-evaporation crystallization method of scheelite concentrate. As the production process is different, the production equipment is also different. The equipment commonly used in evaporative crystallization method is a jacket-heated enamel reactor with a stirring device and a continuous crystallizer. Other production equipment is liquid nitrogen cooling vacuum dryer.
Use of ammonium paratungstate: as an important intermediate in tungsten metallurgy industry, APT can not only be used to produce tungsten oxide, ammonium metatungstate, metal tungsten powder, tungsten strip, tungsten wire and hard alloy, but also can be used as colorant in ceramic industry, catalyst in petrochemical industry, water absorbing gel in chemical industry.
APT marks, packaging, transportation and storage should be noted as follows: (1) Marks: the name of the supplier, product name, brand number, specification, batch number and net weight should be indicated on the outer package of the product, and words or marks such as “Moisture-proof” and “upward” should be attached; (2) Packaging: plastic woven bags or iron drums are used for the outer packaging of the products, and polyethylene plastic bags are used for the inner packaging, which is tightly sealed; (3) Transportation and storage: When the product is transported and stored, it should be prevented from dampness and violent collision.
