Common sulfur salts and species in water: solubility and treatment
Sulfur occurs in water in several dissolved forms. Sulfate (SO42−) is common in groundwater, seawater and industrial brines. Reduced sulfur can occur as hydrogen sulfide (H2S) and hydrosulfide (HS−); sulfite (SO32−) and thiosulfate (S2O32−) occur in some process waters. Soluble salts dissociate into ions, and the species present depends on pH, redox conditions, temperature and other constituents.
Common sulfur salts and species
These are indicative pure-water solubility values, not predictions for mixed brines. Temperature, hydration state, common ions and water chemistry can change solubility. Hydrogen sulfide is a dissolved species, not a salt.
| Salt or species | Formula | Indicative solubility | Where it may occur |
|---|---|---|---|
| Sodium sulfate | Na2SO4 | About 28.1 g/100 g water at 25 °C | Natural waters, seawater and saline process brines |
| Magnesium sulfate | MgSO4 | About 30 g/100 mL water at 20 °C | Seawater, mineral waters and RO or evaporator concentrates |
| Potassium sulfate | K2SO4 | About 12 g/100 mL water at 25 °C | Fertilizer, mining and specialty chemical process streams |
| Ammonium sulfate | (NH4)2SO4 | About 76.7 g/100 g water at 25 °C | Fertilizer production and ammonium-bearing industrial waters |
| Calcium sulfate (gypsum) | CaSO4 | About 0.2 g/100 mL water at 20 °C | Hard waters, desalination concentrates and industrial brines; may form scale |
| Barium sulfate (barite) | BaSO4 | About 0.00031 g/100 g water at 20 °C | Produced waters, mining waters and barium-bearing sulfate streams |
| Sodium sulfite | Na2SO3 | About 22 g/100 mL water at 20 °C | Dechlorination and chemical process waters |
| Sodium thiosulfate | Na2S2O3 | About 20.9 g/100 mL water at 20 °C | Mining and chemical process streams |
| Hydrogen sulfide / hydrosulfide | H2S / HS− | Depends on pH, temperature and pressure | Groundwater, anaerobic and geothermal waters, and some mine or industrial drainage |
Treatment and separation options
Process selection depends on sulfur species, concentration, pH, redox state, other ions and the required water quality or recovered product. A representative water analysis and, where appropriate, treatability testing help select a suitable process.
| Challenge | Potential approach | Key consideration |
|---|---|---|
| Sulfate in brackish water or saline feed | Nanofiltration or reverse osmosis | Moves sulfate into a concentrate; scaling and concentrate management matter. |
| Low sulfate in high-purity water | Ion exchange or a suitable membrane process | Consider competing ions, target concentration and regeneration or reject handling. |
| Sulfate-rich brine for concentration or recovery | Electrodialysis, electrodialysis reversal, evaporation and crystallisation | Recovery and product purity depend on mixed-salt composition and process configuration. |
| Gypsum or barite scaling risk | Scaling assessment, pretreatment, antiscalants, or precipitation with solids separation | Risk depends on ion activities, temperature and concentration—not sulfate alone. See the calcium sulfate scaling calculator as an illustrative tool. |
| Hydrogen sulfide, sulfite or thiosulfate | Species-specific oxidation followed by filtration or other solids separation; adsorption or biological treatment may also suit some waters | Check oxidation chemistry and by-products for the actual stream. Sulfide can create odor and exposure concerns. |
Membrane and electrodialysis processes transfer dissolved salts into a concentrate rather than destroying them. Concentrate, regeneration waste and precipitated solids need a suitable recovery, reuse or disposal route. Sulfate in mine drainage may accompany acidity and dissolved metals, so treatment should address the overall water chemistry.
Discuss a water-treatment challenge
Share the water composition and treatment objective with Lenntech to discuss possible separation or treatment options.
Discuss a water-treatment challenge
To discuss a specific water or brine composition, contact Lenntech at info@lenntech.com.
Sources and further reading
- WHO: Chemical fact sheet — hydrogen sulfide
- USGS: Mine drainage
- U.S. EPA: Treatment technology data — sulfate in mining wastewater
- PubChem: Sodium sulfate
- ILO/WHO: Magnesium sulfate
- ILO/WHO: Potassium sulfate
- PubChem: Ammonium sulfate
- PubChem: Calcium sulfate
- PubChem: Barium sulfate
- ILO/WHO: Sodium sulfite
- ILO/WHO: Sodium thiosulfate
Last reviewed: 8 November 2026 by Lenntech