Common arsenic salts and compounds in water
Arsenic salts are sources of dissolved arsenic, but the original salt name does not describe the species that persist in water. Oxidation state, pH and reactions with iron minerals often control removal more strongly than the starting counter-ion.
See also arsenic in water and the arsenic element page.
Selected salts and compounds
This is a practical selection, not a ranking of abundance in every water. Qualitative solubility descriptions refer to the stated compound; hydration, temperature, pH and complexation can change its behaviour. A soluble starting salt does not necessarily remain unchanged after addition to water.
| Compound | Formula or form | Behaviour in water | Practical relevance |
|---|---|---|---|
| Sodium arsenite | NaAsO2 | Water-soluble As(III) source. | In many near-neutral waters, As(III) is largely present as uncharged arsenous acid, H3AsO3. |
| Disodium hydrogen arsenate | Na2HAsO4 · variable hydration | Water-soluble As(V) salt. | Dissociation produces arsenate; its protonation and charge depend on pH. |
| Calcium arsenate | Ca3(AsO4)2 | Less soluble than the sodium salts; behaviour depends on solution conditions. | A low-solubility solid is not a guarantee of low dissolved arsenic under changing pH and water chemistry. |
| Arsenic trioxide (oxide, not a salt) | As2O3 | Can dissolve and supply As(III). | Included because industrial residues and weathering can release arsenic without an initial soluble arsenite salt. |
Removal, purification and recovery
For As(III)-bearing water, oxidation to As(V) can improve subsequent removal by iron-based adsorption or coagulation and filtration. Oxidation alone does not remove arsenic. Evaluate oxidant demand, pH, phosphate, silica and other competing constituents before selecting a process.
Iron-based adsorptive media, ferric coagulation/co-precipitation, suitable anion exchange and reverse osmosis are established options, with different pretreatment and residual-management needs. Confirm performance with the actual feed water and monitor breakthrough or treated-water arsenic. Spent media, sludge, regenerant and membrane concentrate retain the removed arsenic.
Information for process selection
Useful inputs include flow, pH, temperature, salinity, total and dissolved arsenic, other metals, suspended solids and known complexing constituents. Define the treated-water target and whether recovery is an objective. Laboratory or pilot testing can establish performance for the actual feed rather than a simplified salt solution.
Discuss your water-treatment application
Contact Lenntech at info@lenntech.com to discuss your water composition and treatment objective.