What Is Ammonium Metatungstate?

Ammonium metatungstate (AMT) produced by CTIA GROUP LTD is an inorganic composite salt with the molecular formula H₂₈N₆O₄₁W₁₂, formed by the combination of ammonium cations and metatungstate anions. It appears as a white crystalline powder or slightly yellowish solid. At the microscopic level, its atoms are arranged in an orderly manner through specific chemical bonds, forming a stable chemical structure that endows AMT with unique chemical properties.

I. Basic Properties of Ammonium Metatungstate

Solubility: AMT is highly soluble in water, with a solubility of up to 300 g/100 ml at 20°C, making it advantageous in applications involving aqueous solutions. For instance, it is often used to prepare high-concentration tungstate solutions free of alkali metal ions due to its excellent water solubility. In contrast, ammonium paratungstate (APT) is only slightly soluble in water, which is a key distinguishing feature between the two compounds.

Thermal Stability: AMT exhibits high thermal stability, capable of withstanding high temperatures without decomposition. This property ensures its chemical stability in industrial processes requiring high-temperature treatments, such as calcination to produce other tungsten compounds, providing a reliable raw material foundation for subsequent reactions.

Acidic Aqueous Solution: When dissolved in water, AMT initiates a hydrolysis process. Under the influence of water molecules, its ionic structure breaks down, with ammonium ions combining with hydroxide ions in the water, while metatungstate anions induce partial ionization of water molecules, releasing hydrogen ions. As the concentration of hydrogen ions increases, the solution’s pH decreases, resulting in an acidic solution.

Crystal Morphology: Through spray drying, AMT can form spherical crystals with a particle size reaching 200 mesh. This specific crystal morphology and particle size distribution make it highly effective in applications requiring specific material forms, such as catalyst carrier preparation, where spherical crystals enhance the catalyst’s specific surface area and catalytic efficiency.

II. perse Production Processes for Ammonium Metatungstate

Thermal Decomposition Process

This process uses APT as the primary raw material, supplemented by a small amount of citric acid as a catalyst. After thorough mixing, the materials are heat-treated in a far-infrared rotary furnace. During this process, APT releases some ammonia and water, and the decomposition products are quickly prepared into a slurry. Ammonia water is added to adjust the pH, followed by boiling. Through evaporation, concentration, crystallization, filtration, and granulation, AMT powder is obtained.

Acid Neutralization Process

This method employs APT and nitric acid as raw materials. APT is dissolved in deionized water, mixed with a small amount of ammonium citrate, and formulated into a slurry with a WO₃ content of 12%-30%. The slurry is mixed with nitric acid, maintaining a pH of 2-4. The slurry is heated to 80-90°C, stirred, and kept at constant temperature and volume. After the reaction, the mixture is aged for several hours. The resulting clear liquid is concentrated to a WO₃ content of about 50%, filtered to remove insoluble impurities, further concentrated, cooled, crystallized, and dried to produce AMT.

Solvent Extraction Process

This process uses an organic extractant, such as di(2-ethylhexyl) phosphoric acid or tributyl phosphate, mixed with kerosene to form an organic phase. An ammonium tungstate solution is combined with the organic phase, and the extractant reacts with ammonium ions to adjust the pH to 2-4. The reaction liquid is boiled to form an AMT solution, which is then concentrated, crystallized, filtered, and dried to obtain the final product.

Ion Exchange Process

Starting with APT, the material is heated at 140°C for several hours. The heated product is made into a slurry and boiled to produce an AMT solution. The solution undergoes concentration, crystallization, filtration, separation, and drying to yield AMT. During the ion exchange process, a strongly acidic cation exchange resin (e.g., 732# resin) is typically used, where hydrogen ions on the resin exchange with ammonium ions in APT, facilitating AMT formation.

III. Applications of Ammonium Metatungstate

Key Raw Material for Tungsten Powder Production

In metal processing and alloy manufacturing, AMT plays a critical role as a precursor for producing metallic tungsten. Through hydrogen reduction, AMT can be converted into high-purity tungsten powder, a process governed by strict operational and technical standards. This high-purity tungsten powder serves as a foundational material for producing tungsten alloys and hard alloys.

Application in Petroleum Refining

In petroleum refining, AMT is a core raw material for tungsten-based catalysts, playing an irreplaceable role. Catalytic cracking, a key step in refining, breaks long-chain hydrocarbons into shorter-chain molecules to produce fuels like gasoline and diesel, as well as chemical feedstocks like ethylene and propylene. AMT-derived catalysts, with their unique acidity and redox properties, effectively promote cracking reactions.

Application in Exhaust Gas Treatment

With increasingly stringent environmental regulations, exhaust gas treatment has become a vital task in the energy and environmental sectors. AMT is primarily used in the production of denitration catalysts to adsorb pollutants like sulfur and nitrogen oxides from coal-fired power plant emissions. AMT-based denitration catalysts typically use titanium dioxide (TiO₂) as a carrier, with AMT loaded onto the carrier through specialized processes to form highly active and stable catalysts.

Application in the Ceramics Industry

In the ceramics industry, AMT enhances the strength and insulation properties of ceramic products. Traditional ceramics often face limitations in strength and insulation, restricting their use in high-end applications. By adding an appropriate amount of AMT to ceramic formulations and processing through high-temperature sintering, the crystal structure of ceramics becomes denser, improving strength. Additionally, AMT enhances the electrical properties of ceramics, increasing their insulation performance.

IV. Safety Precautions and Operational Guidelines

AMT is not entirely harmless, and its potential hazards must be fully understood during use and handling. From the perspective of chemical hazard classification, AMT exhibits the following risks:

Acute Toxicity: Harmful if swallowed, meaning ingestion into the digestive system can harm human health.

Eye Damage: Causes severe eye irritation. Contact with AMT particles or solutions can strongly irritate the eyes’ mucous membranes and tissues, potentially causing pain, redness, tearing, or, if untreated, irreversible vision damage.

Given these hazards, strict protective measures must be implemented during handling to ensure personnel and environmental safety:

Wear Protective Equipment: Operators must wear protective gloves, goggles, and dust masks throughout the handling process.

Avoid Skin Contact and Ensure Cleanliness: Direct skin contact with AMT should be minimized. After operations, thoroughly clean the skin to prevent residual AMT from causing potential harm.

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