Common tungsten salts and compounds in water: solubility and treatment
Tungsten-bearing waters and process liquors may contain dissolved tungstate, polytungstate species, suspended tungsten minerals, or soluble tungstate salts added during processing. “Common tungsten salts” therefore includes both compounds used in hydrometallurgy and mineral phases that can occur in ore or treatment residuals. Solubility depends on pH, temperature, oxidation state, ionic strength and the specific hydrate or polytungstate salt form.
Representative tungsten compounds and their aqueous solubility
The values below are published reference values for specified compounds and conditions. They are not interchangeable design data: hydrate state, temperature and the reporting basis can change the result. In process brines, co-existing ions and pH can shift speciation and precipitation behaviour.
| Compound | Formula or form | Indicative water solubility | Where it may be encountered |
|---|---|---|---|
| Sodium tungstate, anhydrous | Na2WO4 | About 742 g/L at 20 °C (reported value) | Alkaline leach liquors and tungsten chemical manufacture |
| Sodium tungstate dihydrate | Na2WO4·2H2O | About 909 g/L at 20 °C (reported value for the hydrate) | Commercial reagent, leaching and solution preparation |
| Sodium metatungstate | Hydrated polytungstate salt | Reported as greater than 1,000 g/L near 20 °C | Specialty chemical solutions and tungsten processing |
| Ammonium metatungstate | Hydrated polytungstate salt | Reported about 1,635 g/L at 22 °C | Concentrated tungsten process solutions and catalyst applications |
| Ammonium paratungstate (APT) | Hydrated ammonium polytungstate | Reported about 270 g/L at 20 °C | Crystallized intermediate in tungsten refining |
| Calcium tungstate (scheelite) | CaWO4 | Sparingly soluble; apparent dissolution depends strongly on pH and solution chemistry | Tungsten ore, mineral residues and calcium-based precipitation products |
| Tungsten trioxide / tungstic acid | WO3 / hydrated WO3 | Low solubility in water; dissolution increases in suitable alkaline or reactive media | Roasting products, refining intermediates and solids in process streams |
High reported solubilities for sodium and ammonium polytungstates describe particular concentrated solutions and should not be interpreted as universal equilibrium limits in natural water. In dilute waters, tungstate speciation and sorption to solids are often more important than saturation with a tungsten salt.
Removal, purification and recovery technologies
Choose treatment based on dissolved versus particulate tungsten, concentration, pH, redox conditions, salinity, competing ions and whether the goal is discharge, reuse or product recovery.
- Solids separation: clarification, coagulation, microfiltration or ultrafiltration can remove mineral particles and tungsten-bearing floc. These steps do not remove dissolved tungstate without a preceding capture or precipitation step.
- Adsorption and co-precipitation: iron oxyhydroxide media and ferric floc can capture tungstate under suitable pH conditions. Calcium- or aluminium-bearing solids may also promote capture or precipitation. Phosphate, sulfate, silica, natural organic matter and high salinity can affect performance; jar tests and residuals evaluation are important.
- Anion exchange: strong-base or selected anion-exchange systems can capture tungstate from suitable process liquors and can be used for separation or concentration. Competing anions, resin selectivity, regeneration chemistry and treatment of the eluate determine feasibility.
- Selective precipitation and crystallization: controlled chemical processing can transfer tungsten into calcium tungstate or recover purified tungsten products, including ammonium paratungstate, from concentrated streams. The correct reagent and conditions depend on the feed composition and the desired product.
- Nanofiltration or reverse osmosis: membranes may separate water from dissolved salts and concentrate tungsten-bearing streams when osmotic pressure, scaling and membrane compatibility allow. They generally do not selectively recover tungsten from mixed brines by themselves; the concentrate still requires management or downstream recovery.
For a specific water or process liquor, characterize both filtered and unfiltered samples where particles may be present. Bench testing with representative water helps determine whether capture, separation, concentration or recovery is practical.
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Lenntech’s engineering team can assess water and process streams for separation, purification and concentration options.
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Last reviewed: 8 November 2026 by Lenntech.
Sources and further reading
- US EPA: Sodium tungstate toxicological review and reported solubility data.
- International Tungsten Industry Association: Tungsten compounds and published solubility data.
- ATSDR: Toxicological Profile for Tungsten — environmental chemistry and fate.
- Review: Treatment and recycling of tungsten beneficiation wastewater.
- Review: Hydrometallurgical recovery of tungsten from primary and secondary materials.
- Study: Calcium-bearing phases and scheelite formation for tungsten removal.