Ammonium Maratungstate Prepared from Ammonium Tungstate by Ion Exchange

At the present time, crystalline ammonium metatungstate (AMT) is being produced from APT. Although this process overcomes some of the disadvantages of the-prior art, in practice it is somewhat difficult to control for maximum conversion. As a consequence, on crystallization of AMT from solution, the residual APT must be removed in order to produce completely water-soluble AMT products. Another disadvantage of this process is its intermittent batch nature, requiring baking, digesting, filtering and concentrating of solutions before crystallization. On a production scale, such stepwise operations tend to be time consuming and costly.

ammonium metatungstate AMT image

As an improvement over the above process, a method of ion exchange for producing ammonium maratungstate directly from ammonium tungstate (AT) solution is came up with. AT solution is contacted with a liquid extraction system consisting of Di-Z-ethyhexyl phosphoric acid (D-2-EHPA)-tri-n-butyl phosphate (TBP)- kerosene, which extracts ammonium ion and rapidly lowers the pH to the AMT-forming region. The solution is then digested to allow formation of AMT.

While this method substantially avoids the formation of APT and is amenable to continuous processing, it has not found widespread use due to a tendency toward instability of the organic system, and resultant formation of insoluble phospho-tungstates in amounts up to percent or more of the total solid product, depending upon the conditions of formation.

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Ammonium Metatungstate Preparation-Thermal Decomposition Method

Ammonium Metatungstate Picture

The thermal decomposition method of ammonium paratungstate to prepare ammonium metatungstate: ammonium paratungstate and a small amount of citric acid catalyst after mixing into the far infrared, rotary furnace, controlled thermal decomposition temperature 200 ～ 280 ℃, decomposition of about 1 h. The removal of ammonia and water, ammonium paratungstate weightlessness rate was 5% ~ 6%.

The thermal decomposition products immediately after the slurry, adding proper amount of ammonia, Ph value is adjusted in the 3 to 4 range, at 90 ℃ digestion slurry. After evaporation to ammonium metatungstate content of 50% can be used as a liquid product to sell, crystallization, when the evaporation to the original volume of 20% filtering and separating, granulating product. Also can be evaporated and concentrated liquid product is prepared by spray drying. As of 45% ~ 50% ammonium metatungstate by high-speed centrifugal rotary spray dryer, imports of hot air temperature 250～300 ℃, outlet temperature 90 ～ 95 ℃, the obtained product is a spherical crystal, particle size is 200 mesh accounted for 95%, free water <1.5%.

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Ammonium Metatungstate New Producing Method

Ammonium metatungstate  new producing method is Using a coupling process of neutralization–nanofiltration–crystallization, pure ammonium metatungstate (AMT) was prepared. The effects of chemical neutralization of ammonium paratungstate (APT) by nitric acid, operating pressure, AMT concentration, the volume of washing water on the coupling process were systematically discussed. It was found that the better conditions of AMT preparation were as follows: the neutralization temperature was 80–95 °C, pH value was 2.0–3.5; the operating pressure of HDS-12-2, nanofiltration was 1.5–2.0 MPa, the density of AMT crystallization solution was 2.39 kg/L, and then cooling. APT conversion efficiency (δ) to AMT was more than 97.62%. The removal ratio of nitrate ion (NO3−) was more than 99% while AMT rejection (RAMT) was 99.9%. Besides, small-grained, even-proportioned, white-colored and high-purified AMT crystal was be obtained and analyzed. This method has several advantages such as simple technological process, short production cycle, lower environmental pollution and high quality.

ammonium metatungstate AMT picture

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Ammonium Metatungstate Properties

Ammonium metatungstate is also called AMT, it is inorganic chemical product. Its molecular formula is H₈N₂O₄W  and molecular weight is 283.9145. CAS number is 11120-25-5;14311-52-5. Ammonium metatungstate properties include white or slightly yellow crystals which has no harmful components and slightly acidic. The solubility in water is 303.99/loogH:O when 20℃, aqueous fairly stable. It is insoluble in alcohol.

Its molecular structure is listed as below:

ammonium metatungstate molecular structure

Ammonium metatungstate can be used as catalysts, capacitors, nuclear shielding, flame retardants, corrosion inhibitors raw materials, but also excellent raw materials in the preparation of ultra fine tungsten powder, tungsten heavy alloy powder, phosphotungstic acid, arsenic acid, silicon tungstate. It can also be used as reagents for chemical analysis such as for chemical diagnosis; source material for the preparation of high purity tungsten trioxide used as a thin film substrate for certain semiconductor devices; high purity source material for research in tungsten chemistry; source material for DENOX catalysts industry; as a precursor to a variety of POM (polyoxometalates).

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Ammonium Metatungstate Preparation-Neutralization Method

Ammonium metatungstate, also known as AMT, is a tungsten chemical in the form of highly soluble hydrated crystals, solubility is 303.99/loogH:O when 20℃, aqueous fairly stable. It is white or slightly yellow crystals which has no harmful components and slightly acidic.

Neutralization method with secondary ammonium metatungstate and Nitrate as the raw material purchase ammonium metatungstate: secondary ammonium metatungstate deionized water and ammonium citrate with WO₃ 12%~ 30% concentration of slurry. According to =1:20: nitrate ammonium paratungstate by adding 3% ~ 5% of dilute nitric acid to ammonium paratungstate slurry, control ratio of solid to liquid 1: (3 ~ 4), the Ph value of 2 ~ 4, heating and dissolving solution, the relative density of 1.18 ~ 1.20, heating to 80 ~ 90 ℃, constant temperature and constant volume control Ph value, the stirring reaction for 4H hours, aging, concentrating the supernatant to WO₃ content is about 50-, filtration to remove insoluble, liquid concentration, cooling crystallization, continue to 80 ℃ drying.

ammonium metatungstate crystal

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Ammonium Metatungstate Modified Borated Zirconium

Samples of tungsten-modified borated zirconium were prepared to be used as catalyst in 2-phenoxyethanol acetylation. The borated zirconias were obtained by impregnation of two zirconias (S2 and S4) obtained by the micellar method using different zirconium precursor concentrations with boric acid solution containing 0.3 moles B/dm³. These solids and the parent zirconias were impregnated with two concentration levels of ammonium metatungstate solutions (0.11 and 0.22 moles W/dm³). The solids containing boron mainly have amorphous characteristics and strong acidity, while those that contain only tungsten showed stronger acidity and evidence of the presence of a crystalline phase.

The specific surface area and the pore volume slightly decreased in the solids obtained by adding tungsten to borated zirconia, and more markedly in those that contain only tungsten, and the mean pore size increased with respect to the parent support. It was observed that in the 2-phenoxyethanol acetylation using acetic acid as acylating agent and tungsten-modified borated zirconia as catalyst, the yield to acetylated product was high and it is correlated with the acid strength of the catalysts. In turn, the solids that contain only tungsten have a correlation with the acidity, but lead to low yield values due to a poorer dispersion of the tungsten species. The best yield was obtained with the catalyst prepared with the borated S4 zirconia containing 15% g B₂O₃/100 g support and 12.5% g W/100 g support. Using this catalyst and the same reaction conditions, the acetylation of different alcohols and phenols was studied, the reactivity order being as follows: primary alcohols > secondary alcohols > phenols.

Ammonium Metatungstate AMT

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