What is Ammonium Paratungstate?
Ammonium Paratungstate is an inorganic tungsten compound produced by hydrometallurgical processing of tungsten ore. It serves as the primary precursor for tungsten trioxide (WO₃), tungsten blue oxide (TBO), tungsten metal powder, tungsten carbide, and ammonium metatungstate (AMT). It is the entry point for virtually all downstream tungsten chemistry. APT appears as white crystals in either flake or needle form, depending on the crystallisation conditions. It is slightly soluble in water (less than 2% at 20°C) and insoluble in alcohol.
Ammonium paratungstate is also known as: Ammonium Tungstate, Ammonium Wolframate, APT, and Decaammonium tungstate.
Physical and chemical properties of Ammonium Paratungsate (APT)
Ammonium Paratungstate (APT) is a white crystalline powder, commonly with the formula or, used primarily as a precursor for tungsten products. Key properties include a decomposition temperature around 600°C (yielding tungsten trioxide), slight solubility in water (<2% at 20°C), and insolubility in alcohol.
- CAS Number: 11120-25-5
- EINECS Number: 234-364-9
- Solubility: Slightly soluble in cold water; solubility improves in hot water, but it is insoluble in ethanol.
- Melting Point: Decomposes before melting, with decomposition occurring around 600 °C.
- Stability: Stable under recommended storage conditions (room temperature)
- Molecular Formula: (NH₄)₁₀[H₂W₁₂O₄₂]·4H₂O
- Simplified Commercial Notation: 5(NH₄)₂O·12WO₃·5H₂O
- Molecular Weight: 3,132.46 g/mol
- Appearance: White crystalline powder or needle-like crystals.
Grades and Specifications
APT is produced in several grades defined by purity, WO₃ content, particle size, and crystal morphology. The Chinese national standard GB/T 10116 defines APT grades and is widely referenced in global supply.
Industrial Standard Grade: (APT-0 / APT-1) The most widely traded grade, with a WO₃ content of ≥88% and purity in the range of 99.0–99.5%. This grade is suitable for most carbide and alloy production applications where sub-ppm impurity control is not required. It is the benchmark grade used in global APT commodity pricing.
High Purity Grade: With a purity of ≥99.9% and WO₃ content of ≥88%, APT is used in applications that demand tighter impurity control. This includes high-performance tungsten alloys, catalyst production, and AMT manufacture. Key impurities, including Mo, Fe, K, Na, Si, P, and As are controlled to low single-digit ppm levels.
Ultrapure Grade (4N): Ultrapure APT achieves purity of ≥99.99% and is the starting material for tungsten sputtering targets used in semiconductor thin-film deposition, precision tungsten wire, and advanced electronic components. All trace element impurities are controlled to below 10 ppm. This grade requires stringent quality management and lot-by-lot ICP-MS verification.
Research and ACS Reagent Grade: The highest purity tier at ≥99.999%, reserved for analytical chemistry, electrochemistry research, reference standards, and materials science applications where absolute tungsten purity is required. Supplied in smaller quantities with full analytical certification.
Key Impurities Monitored Regardless of grade, the following impurities are tracked in COA documentation: molybdenum (Mo), iron (Fe), potassium (K), sodium (Na), silicon (Si), phosphorus (P), arsenic (As), manganese (Mn), copper (Cu), and nickel (Ni). For standard industrial grades, these are present in the low ppm range; for high purity and ultrapure grades, they are controlled to single-digit or sub-ppm levels.
Uses of Ammonium Paratungsate
Tungsten Metal Powder: APT is thermally decomposed to WO₃ or blue tungsten oxide, then hydrogen-reduced to elemental tungsten powder. The purity of the tungsten powder is of particular importance in all applications and is mainly influenced by the purity of the original ammonium paratungstate, with typical upper limits of trace element concentrations in the low ppm range.
Cemented Carbide (Tungsten Carbide): Tungsten metal powder is mixed with carbon black and treated at temperatures between 1,300 and 2,200°C in a hydrogen atmosphere to produce tungsten carbide powder (WC). Due to its high hardness and comparatively high toughness, it is the main constituent in cemented carbide (hardmetal), a tungsten carbide cobalt alloy.
Ammonium Metatungstate (AMT): AMT is produced by partial thermal decomposition of APT at 220–280°C. AMT is used to produce tungsten chemicals and catalysts because of its excellent water solubility, over 2,200 g WO₃ per litre at 80°C. This high solubility makes AMT ideal for catalyst impregnation applications where APT's low solubility would be impractical.
Tungstic Acid: Acid treatment of APT produces high-purity tungstic acid (H₂WO₄), which is used as a specialised precursor for ultrafine tungsten and tungsten carbide powders in advanced material applications.
Tungsten Wire: Tungsten powder produced from APT is drawn into wire for incandescent and halogen lamp filaments, TIG welding electrodes, vacuum furnace heating elements, and electron beam equipment. Non-sag wire performance depends on trace doping elements carefully controlled at the APT stage.
Ammonium Paratungstate Manufacturing Process
APT is produced through a hydrometallurgical process starting from tungsten ore concentrates — primarily scheelite (CaWO₄) and wolframite ((Fe, Mn)WO₄) — or from recycled tungsten scrap.
Step 1: Leaching: Wolframite is digested in sodium hydroxide (NaOH) solution, while scheelite is processed via sodium carbonate autoclave leaching or acid leaching. Both routes produce a crude sodium tungstate solution.
Step 2: Purification:The crude solution is treated to remove impurities — silica by pH adjustment, molybdenum by sulfide precipitation, and phosphorus and arsenic by selective precipitation. Ion exchange or solvent extraction then converts sodium tungstate into an ammonium tungstate solution.
Step 3: Crystallisation: The purified solution is concentrated by evaporation. As pH drops and WO₃ concentration rises, APT crystallises out of solution. Crystallisation temperature controls crystal morphology — below 50°C produces flake crystals (A-series), above 50°C produces needle crystals (B-series).
Step 4: Filtration, Drying and Screening Crystals are filtered, washed, dried, and screened to achieve the target particle size and purity specification for the intended grade.
APT is produced through a hydrometallurgical process starting from tungsten ore concentrates — primarily scheelite (CaWO₄) and wolframite ((Fe, Mn)WO₄) — or from recycled tungsten scrap.
Step 1: Leaching: Wolframite is digested in sodium hydroxide (NaOH) solution, while scheelite is processed via sodium carbonate autoclave leaching or acid leaching. Both routes produce a crude sodium tungstate solution.
Step 2: Purification: The crude solution is treated to remove impurities — silica by pH adjustment, molybdenum by sulfide precipitation, and phosphorus and arsenic by selective precipitation. Ion exchange or solvent extraction then converts sodium tungstate into a purified ammonium tungstate solution.
Step 3: Crystallisation: The purified solution is concentrated by evaporation. As pH drops and WO₃ concentration rises, APT crystallises out of solution. Crystallisation temperature controls crystal morphology — below 50°C produces flake crystals (A-series), above 50°C produces needle crystals (B-series).
Step 4: Filtration, Drying and Screening Crystals are filtered, washed, dried, and screened to achieve the target particle size and purity specification for the intended grade.
Ammonium paratungstate price and market trends
China dominates global supply, accounting for roughly 75% of global APT production. The price surge is driven by environmental restrictions on Chinese mining, strict national quota systems, declining ore grades, and critically low global inventories. Analysts have warned the world has "sleepwalked" into a tungsten supply crunch, with another deficit forecast for 2026.
APT prices have surged dramatically in 2025–2026, breaking out of their long-term average of around US$300 per mtu to trade at approximately US$1,750–1,850 per mtu CIF Rotterdam as of February 2026. The global APT market was valued at approximately US$150 million in 2024 and is projected to reach US$250 million by 2033, growing at a CAGR of 6.3%. For industrial buyers, long-term supply contracts and supplier diversification are more critical now than at any point in recent history.
Frequently Asked Questions
1. What is Ammonium Paratungstate used for?
APT is the primary precursor for tungsten metal powder, tungsten carbide, tungsten alloys, and tungsten wire — together accounting for the majority of global tungsten consumption. It is also used in catalyst production, sputtering targets, tungsten trioxide, and ammonium metatungstate (AMT) manufacturing.
2. What is the difference between APT and AMT?
APT (CAS 11120-25-5) and AMT (CAS 12028-48-7) are related but not interchangeable. APT is barely soluble in water (<2% at 20°C), making it ideal for solid-state tungsten powder and carbide production. AMT is highly water-soluble (>300 g WO₃/100 mL at 25°C), making it the preferred choice for catalyst impregnation. Different CAS numbers, different applications.
3. How is APT priced, and what drives price changes?
APT is priced per metric tonne unit (mtu) of WO₃ — one mtu equals 10 kg of WO₃. As of early 2026, prices are around US$1,750–1,850 per mtu CIF Rotterdam. Prices are primarily driven by Chinese supply policy, mining quotas, and export restrictions, since China controls roughly 75% of global APT production.
4. What purity grade of APT do I need?
Standard industrial grade (99.0–99.5%) suits most carbide and alloy applications. High purity (≥99.9%) is required for catalysts and high-performance alloys. Ultrapure (≥99.99%) is necessary for sputtering targets and semiconductor applications. Always request ICP-MS verified COA documentation specifying Mo, K, Na, Fe, and Si impurity limits.
5. How should APT be stored, and what is its shelf life?
Store in tightly sealed double-bag iron drums in a cool, dry environment away from moisture. APT is mildly hygroscopic — humidity exposure affects crystal morphology and downstream reduction behaviour. Shelf life is approximately 2 years under correct storage conditions.