Common boron salts in aqueous solutions and their removal/purification technologies
Boron in natural and industrial waters is measured as total boron, but its dissolved form changes with pH and water chemistry. Boric acid and borate species are the main aqueous forms; borate minerals and boron-bearing salts can be sources in groundwater, process water and concentrated brines.
Managing elevated boron in a water supply, process stream or brine? Treatment choice depends on boron speciation, salinity, the required water quality and how concentrate or regeneration waste will be handled.
Common boron salts and forms in water
The table distinguishes compounds used or found as solids from the dissolved species measured in water. A laboratory result is normally reported as boron (B); it does not establish that a specific intact salt is present in the sample.
| Boron compound or form | Formula | Typical application / industry / where used | Typical aqueous streams where encountered | Solubility and water behaviour |
|---|---|---|---|---|
| Boric acid | H3BO3 or B(OH)3 | Glass, ceramics, chemical products and boron compounds. | Seawater, groundwater influenced by borate geology, geothermal waters and industrial process water. | Water-soluble; about 4.72% w/w at 20 °C in the cited fact sheet. Solubility increases with temperature. In most near-neutral freshwaters it is the main dissolved form. |
| Sodium tetraborate decahydrate (borax) | Na2B4O7·10H2O | Glass and enamel manufacture, cleaning products and borate processing. | Runoff or process waters near borate deposits, borax handling and industrial cleaning or manufacturing. | Water-soluble; about 4.71% w/w at 20 °C in the cited fact sheet. Hydrate form and temperature affect the value. Dissolved borax contributes sodium and borate-related species. |
| Other sodium tetraborate hydrates | Na2B4O7·5H2O; Na2B4O7 | Industrial borate products, glass, detergents and chemical manufacture. | Process rinses, product dissolution and borate-rich brines. | Soluble, with solubility dependent on temperature and hydration state; values should not be compared without specifying the solid form and measurement basis. |
| Sodium metaborate (hydrated forms) | NaBO2·nH2O | Specialty chemical manufacture and alkaline cleaning formulations. | Industrial wash water and borate-processing solutions. | Readily soluble; aqueous speciation depends on concentration, pH and temperature. |
| Potassium tetraborate (hydrated forms) | K2B4O7·nH2O | Specialty glass, ceramics and laboratory or chemical uses. | Product dissolution and specialty-manufacturing streams; less common than sodium borates. | Soluble; the hydrate and temperature must be specified for a quantitative value. |
| Colemanite and ulexite (natural borate minerals) | Ca2B6O11·5H2O; NaCaB5O6(OH)6·5H2O | Natural borate ores mined for boron products. | Groundwater, drainage and leachates contacting borate deposits, mine workings or tailings. | Mineral dissolution is slower and more limited than dissolution of soluble sodium borates; rates depend on pH, temperature, particle size and water composition. |
| Borate ions in solution | Primarily B(OH)4− at higher pH | Aqueous species rather than a separate dry salt. | Alkaline groundwater, industrial process water and concentrated brines. | Dissolved. Its proportion relative to neutral boric acid increases as pH rises; apparent speciation also depends on salinity. |
Formula note: Ulexite is commonly written NaCaB5O6(OH)6·5H2O (equivalent to NaCaB5O9·8H2O). Use the mineral formula, not a claim that ulexite remains as an intact dissolved molecule.
Why pH matters for boron removal
Boric acid is a weak acid. Near neutral pH, dissolved boron is predominantly neutral B(OH)3; the negatively charged borate ion B(OH)4− becomes more important as pH approaches and exceeds about 9.2 in freshwater. Salinity and ionic strength can shift the apparent transition. Because many analyses report total boron as B, treatment design should consider pH and the full water composition rather than assuming a single salt.
Removal, separation and recovery options
| Objective | Potential technology | Selection notes |
|---|---|---|
| Reduce boron in drinking or process water | Reverse osmosis (RO) | Neutral boric acid is generally rejected less effectively than charged borate. Membrane type, pH, salinity and recovery affect performance. A pH-adjusted second pass or a membrane selected for boron rejection may improve removal; test the actual feed. |
| Polish water for a low boron target | Boron-selective ion exchange or adsorption | Specific media can capture boron, but capacity and selectivity depend on water composition. Regeneration produces a residual stream that needs appropriate management. |
| Remove boron from concentrated brine or recover a boron product | Selective adsorption or ion exchange; solvent extraction; precipitation or crystallisation | These are candidate routes, not universal solutions. Competing salts, boron concentration, product specification, reagent use and residual handling determine feasibility. Pilot or laboratory testing may be appropriate. |
| Reduce overall dissolved salts | Electrodialysis (ED) or a zero-liquid-discharge (ZLD) train | These processes address ionic concentration or brine management, but are not automatically selective boron-removal steps. Boron speciation and the intended product or discharge target must be assessed. |
Conventional coagulation, sedimentation, filtration and chlorination do not usually remove dissolved boron to a significant extent. Select a process from a representative analysis that includes total boron, pH, TDS, major ions, alkalinity, silica, temperature and flow. Consider the fate of RO concentrate, spent media or regeneration solutions in the overall design.
Discuss a water-treatment challenge
Discuss a water-treatment challenge
To discuss a specific water or brine composition, contact Lenntech at info@lenntech.com.
Sources and further reading
- WHO: Boron — occurrence and treatment performance
- Health Canada: Boron — analytical and treatment considerations
- USGS: Chemistry and occurrence of boron in natural water
- National Pesticide Information Center: Boric acid technical fact sheet
- Kim et al. (2023): Boron recovery from salt-lake brine, seawater and wastewater — a review