Common molybdenum salts and compounds: solubility and recovery technologies
Molybdenum compounds occur in natural waters, mine drainage, flotation and roasting liquors, and metallurgical process streams. The compounds differ greatly in water solubility. The figures below are reference data for individual compounds and should not be treated as solubility predictions for mixed brines.
Common molybdenum salts and compounds
In water, molybdate salts dissociate and the dissolved molybdenum species re-equilibrate with pH and concentration. Hydration state and temperature also affect reported solubility. The table therefore distinguishes measured reference values from qualitative descriptions.
| Compound | Formula | Reported solubility in water | Where it is encountered |
|---|---|---|---|
| Sodium molybdate | Na2MoO4 (often dihydrate) | About 394 g/kg water at 25 °C in one government compilation | Soluble molybdate product, reagent or process-stream constituent |
| Ammonium molybdates (including dimolybdate and heptamolybdate) | (NH4)2Mo2O7; (NH4)6Mo7O24·4H2O | Water-soluble; exact value depends on the compound, hydration state and temperature | Purification and crystallisation products in molybdenum processing |
| Molybdenum trioxide | MoO3 | About 1.34 g/kg water at 20 °C in one government compilation; also dissolves in ammonia and alkaline solutions | Roasted molybdenite concentrate and an intermediate for molybdate products |
| Calcium molybdate (powellite) | CaMoO4 | About 50 mg/kg water in one government compilation; source does not specify temperature | Mineral phase in ores, tailings or precipitated solids |
| Molybdenite | MoS2 | Insoluble in water | Primary molybdenum ore and flotation concentrate |
Values are reported from a government reference table and vary among sources and material forms. They are not process design values. For a real stream, use measured chemistry and account for pH, ionic strength, competing ions, temperature and any solids present.
Recovery and treatment technologies
| Stream or objective | Potential approach | Key considerations |
|---|---|---|
| Dissolved molybdate in mine water or wastewater | Ferric coagulation/co-precipitation or iron-oxide adsorption, followed by solids separation | Removal is water-specific; pH and competing anions affect performance. Plan for iron sludge or spent media. |
| Low-concentration polishing or recovery | Anion exchange, if resin selectivity and regeneration suit the stream | Sulfate, phosphate and other anions may compete. Regenerant produces a smaller, more concentrated residual that still requires management or recovery. |
| Concentrated metallurgical liquor | Purification and controlled precipitation/crystallisation of molybdate products | Product yield and purity depend on feed composition, impurities and operating conditions; test the actual liquor. |
| High-salinity water requiring reuse or volume reduction | Conditional NF/RO concentration, electrodialysis or thermal concentration/crystallisation as part of an integrated train | These processes separate or concentrate streams; they are not inherently selective for molybdenum. Osmotic pressure, scaling, competing ions and concentrate disposal constrain the design. |
From molybdenite to molybdenum products
Molybdenite (MoS2) is commonly concentrated by flotation and may be produced as a co-product of copper mining. A widely used processing route roasts concentrate in air at approximately 500–650 °C to convert much of the MoS2 to molybdenum trioxide (MoO3) while releasing sulfur dioxide in the off-gas. After suitable gas treatment, the oxide may be purified or leached in aqueous ammonia to form molybdate solution. Purification and crystallisation can yield ammonium dimolybdate or heptamolybdate; subsequent calcination produces MoO3. Molybdenum metal is made by staged hydrogen reduction. The exact sequence varies with ore, impurity profile and product.
Membranes in saline molybdenum streams
Microfiltration and ultrafiltration can remove suspended solids and floc but do not remove dissolved molybdate. Nanofiltration or reverse osmosis may retain or concentrate molybdate and other dissolved ions where the feed pressure, membrane, salinity and scaling potential permit. Selectivity and concentration factor are feed-specific; neither a universal 10–20× concentration nor a fixed pressure limit applies to every stream.
Electrodialysis transfers ions through ion-exchange membranes and may be evaluated for a particular separation, but selective molybdenum recovery must be demonstrated. Membrane distillation and evaporation can recover water or concentrate salts under suitable conditions; they do not by themselves ensure a pure molybdenum product or zero liquid discharge.
Discuss a molybdenum-bearing water or process stream
Tell Lenntech about the water composition and whether the objective is molybdenum removal, water reuse or recovery. Discuss a water-treatment challenge
Contact Lenntech at info@lenntech.com.
Last reviewed: 8 November 2026 by Lenntech.
Sources and further reading
- Japan Ministry of the Environment: Molybdenum and its compounds — solubility and reference information.
- International Molybdenum Association: Species in aqueous solutions.
- International Molybdenum Association: Molybdenum processing.
- Study: Molybdenum removal from water by ferric coagulation-filtration.
- Review: Technical solutions for molybdenum removal from water.