Silica is important in natural and industrial waters, but the term “silica salts” needs care: dissolved silicon is commonly present as silicic acid, while silicate salts such as sodium silicate are used in some industrial and water-treatment applications. Mineral deposits such as amorphous silica are solids, not dissolved salts.
Key distinction: Water analyses usually report dissolved or total silica as mg/L SiO2 or mg/L Si. These are reporting bases, not proof that a particular salt is present. Identify dissolved, colloidal and particulate forms before selecting treatment.
Common silica and silicate forms in water-related streams
| Form or compound | Formula / description | Typical application / industry / where used | Typical aqueous streams where encountered |
|---|---|---|---|
| Dissolved silica (orthosilicic acid) | Si(OH)4; often reported as SiO2 or Si | Natural dissolved form released as rocks and silicate minerals weather; not a salt. | Groundwater, rivers, cooling-water make-up, boiler feedwater and RO feedwater; concentrations depend on geology and treatment. |
| Sodium silicate (“water glass”) | Na2O·nSiO2; commercial products vary. Sodium metasilicate is Na2SiO3. | Corrosion control, coagulant aid, iron and manganese stabilization, detergents, cleaning and chemical manufacture. | Water-treatment dosing solutions, equipment wash water, detergent and chemical-process wastewater, and streams from silicate production or use. |
| Potassium silicate | K2O·nSiO2; formulation varies | Specialty coatings, agricultural products and chemical manufacture. | Formulation and wash waters where potassium silicate is used; occurrence is process-specific rather than a common natural-water salt. |
| Amorphous silica and colloidal silica | SiO2·nH2O or dispersed SiO2 particles | Can form when dissolved silica becomes supersaturated; colloidal silica may also enter from mineral or process streams. These are silica forms, not salts. | High-recovery RO concentrates, boiler and cooling systems, geothermal or mining waters, and streams handling silica sols or mineral fines. |
| Calcium silicate phases | CaSiO3 and hydrated or mixed mineral phases | Mineral-processing solids and deposits; generally sparingly soluble and composition may vary. | Scale, slurries and solids from mineral processing or high-pH water treatment; not normally a freely dissolved “calcium silicate salt” in ordinary water. |
| Magnesium silicate phases | Hydrated magnesium silicates; mineral composition varies | Mineral solids and process residues; the term covers several phases rather than one universal aqueous salt. | Slurries, mineral-processing effluent and deposits in process equipment; determine solid and dissolved fractions separately. |
| Suspended silicate minerals | Aluminosilicate clays and other silicate particles | Natural geology, erosion and mineral handling; not dissolved salts. | Surface water, mine drainage and mineral-processing water, usually measured as suspended or colloidal material. |
Silica removal and treatment options
The appropriate method depends on whether silica is dissolved, colloidal or particulate, the concentration and pH, temperature, hardness and other ions, and the required water quality. No single method applies to every silica-bearing stream.
| Water-treatment challenge | Potential approach | Important design considerations |
|---|---|---|
| Dissolved reactive silica in demineralized or high-purity water | Strong-base anion exchange in a suitable demineralization train, sometimes with polishing. | Capacity depends on silica loading, pH, competing ions, resin type and regeneration practice. Monitor breakthrough and manage regenerant waste. |
| Dissolved silica in saline or brackish feedwater | Reverse osmosis or nanofiltration, with recovery and pretreatment selected for the feed. | Silica concentrates in the reject. Evaluate saturation, temperature, pH, hardness, colloids and cleaning limits; higher recovery can increase scaling risk. |
| Colloidal or suspended silica | Coagulation/flocculation followed by clarification, filtration or ultrafiltration, as appropriate. | Particle size and surface chemistry affect removal. Jar or pilot testing may be needed, and residual sludge requires management. |
| High silica industrial brine or process water | Selective precipitation or adsorption may be assessed alongside membrane or thermal concentration. | Reagent demand, co-precipitation, solids separation and residual disposal should be tested on representative water; precipitation is not universally selective. |
Use the silica solubility and scaling calculator for an illustrative saturation check, and see RO water chemistry and scaling prevention for silica-related membrane considerations. These tools do not replace a complete water analysis or a validated design model.
Discuss a silica-bearing water or process stream
Share the water analysis, flow, operating conditions and treatment objective. Lenntech can assess separation and concentration options for the specific stream.
Discuss a water-treatment challenge
To discuss a specific silica-bearing water or process stream, contact Lenntech at info@lenntech.com.
Last reviewed: 7 November 2026 by Lenntech.
Sources and further reading
- Australian Drinking Water Guidelines: Silicon and silica.
- U.S. Geological Survey: Silica in natural waters.
- U.S. EPA: Sodium silicate supply-chain profile and water-treatment uses.
- National Research Council: Sodium silicate and activated silica in water treatment.
- Sarabian et al. (2024): Colloidal silica in reverse osmosis treating coal-seam-gas water.
Related pages: Silicon and silica in water, silica breakthrough in demineralizers, reverse osmosis and ion exchange.