Common bromide salts in water: occurrence, solubility and treatment
Bromide in water is present as dissolved Br− ions alongside other ions. Names such as sodium bromide or magnesium bromide describe the salts used to add bromide or the ionic combinations in a brine; they do not normally remain as separate molecules in solution.
This page summarises bromide-bearing waters, representative bromide salts and their approximate solubility in pure water. For an overview of bromide occurrence, water-treatment considerations and industrial recovery, see Bromine in water.
Bromide salts in natural and industrial waters
In freshwater, bromide is generally a minor dissolved constituent. Seawater contains about 65 mg/L bromide on average, with reported concentrations above 80 mg/L in some regions. In seawater and natural brines, bromide occurs together with sodium, magnesium, potassium, calcium and chloride; assigning the dissolved bromide to one specific salt is a useful bookkeeping convention, not a direct description of distinct molecules in the water. Evaporated seawater mother liquor (bittern), inland brines and oilfield formation waters can become much more concentrated.
Industrial bromide streams include bromine-production feed brines and specialty oilfield completion or workover fluids. Calcium bromide and zinc bromide are used in dense clear brines; sodium bromide is also used in completion fluids. Ammonium bromide is more typical of chemical or process streams than natural water. A water analysis should report bromide and the accompanying ions, rather than infer a salt from bromide alone.
Representative bromide salts and solubility
The figures below are approximate solubilities of the pure salts in water near 25 °C, expressed as grams of salt per 100 g of water. They are reference values, not design limits for mixed brines. Hydration state, temperature, pressure and other dissolved salts can alter phase behaviour. All listed salts are highly soluble; bromide usually remains in solution during ordinary water evaporation unless the brine is driven into a specialised salt-recovery sequence.
| Salt | Formula | Approximate solubility near 25 °C | Typical water or process context |
|---|---|---|---|
| Sodium bromide | NaBr | 94.6 g/100 g water | Seawater and natural brines as dissolved ions; bromine-production feed and some completion fluids |
| Magnesium bromide | MgBr2 | About 100.6 g/100 g water; solid hydrate phase affects the reported value | Seawater, saline lakes, deep brines and bittern |
| Potassium bromide | KBr | 67.8 g/100 g water | Dissolved in natural saline waters at lower abundance than sodium and magnesium; chemical and specialty process streams |
| Ammonium bromide | NH4Br | 78.3 g/100 g water | Chemical manufacturing and process solutions; not a principal natural-water salt |
| Calcium bromide | CaBr2 | 156 g/100 g water | Dense clear brines for oilfield completion, workover and packer-fluid service |
| Zinc bromide | ZnBr2 | 471 g/100 g water | Specialty high-density oilfield completion brines, often blended with calcium bromide |
Solubility is stated per mass of water, not per mass or volume of final solution. The values cannot be used to predict when a salt crystallises from a real brine without considering the full ionic composition and temperature-dependent phase equilibria.
Removal, concentration and recovery options
| Objective | Potential approach | Key considerations |
|---|---|---|
| Reduce bromide in dilute or moderately saline water | Bromide-selective ion exchange | Performance depends on resin selectivity, competing chloride and sulfate, operating capacity, regeneration and management of the spent regenerant. |
| Lower dissolved salts in water and transfer bromide to a concentrate | Reverse osmosis | Salt rejection and recovery depend on membrane, feed chemistry and operating conditions. The concentrate remains a bromide-bearing stream requiring a reuse, recovery or disposal route. |
| Separate and concentrate ions in saline feed | Electrodialysis or electrodialysis reversal | Transfers ions through selective membranes into a concentrate. Selectivity and energy use depend on salinity and competing ions; it does not destroy bromide. |
| Recover elemental bromine from bromide-rich industrial brine | Controlled oxidation of Br− to Br2, followed by air or steam stripping and capture | A specialised industrial recovery route involving hazardous, volatile bromine and oxidants; it requires purpose-designed containment and controls. |
| Concentrate mixed brine or reduce liquid discharge | Evaporation and staged crystallisation | These operations concentrate salts but do not selectively remove bromide. Because bromide salts are very soluble, bromide commonly remains in the residual mother liquor or bittern while less-soluble minerals crystallise. |
Conventional clarification and filtration do not reliably remove dissolved bromide. Chemical precipitation can be useful for other constituents in a brine, but should not be assumed to precipitate bromide selectively. Process selection requires the measured water composition, target product or discharge quality, recovery objective and a suitable concentrate-management route.
Discuss a bromide-containing water or brine
For a treatment or recovery assessment, describe the water source, bromide concentration, major ions, flow and process objective to Lenntech.
Discuss a water-treatment challenge
Contact Lenntech at info@lenntech.com.
Last reviewed: by Lenntech.
Sources and further reading
- WHO: Bromide concentrations in fresh water, seawater and desalinated water
- PubChem / HSDB: Sodium bromide properties and solubility
- PubChem: Potassium bromide properties and solubility
- PubChem / HSDB: Calcium bromide solubility
- PubChem / HSDB: Ammonium bromide solubility
- PubChem / HSDB: Zinc bromide solubility
- USGS: Bromide in natural water and brines
- SLB: Clear brines for completion and workover applications
- Health Canada: Bromate formation and membrane treatment references
- US EPA archive: Industrial bromine recovery from brines