AsO4

AsO4 refers to the arsenate group, the arsenate anion with the formula AsO4^3−. It is the tetrahedral oxoanionic form of arsenic in the +5 oxidation state and the fully deprotonated form of arsenic acid, H3AsO4. In aqueous solution arsenic acid is triprotic, with pKa values around 2.2–2.3, 6.9–7.0, and 11.5–12.0; therefore at neutral pH the predominant species are H2AsO4− and HAsO4^2−, while AsO4^3− dominates at high pH.

The AsO4^3− anion features four equivalent As–O bonds in a tetrahedral geometry. It forms a wide range of salts with metal cations and ammonium, such as sodium arsenate and ammonium arsenate. In minerals, arsenate groups appear as part of framework structures related to phosphates and occur in various arsenate-bearing minerals.

Environmental and health aspects: arsenate behaves as a phosphate analog and can interfere with phosphate metabolism in living organisms. While arsenate is generally less acutely toxic than arsenite, it remains toxic and is subject to regulatory controls. Exposure can occur via contaminated water, soil, or food.

Applications and remediation: arsenates have historical use in pesticides and as reagents in analytical chemistry and as fertilizer components. In water treatment, arsenite can be oxidized to arsenate to facilitate removal via adsorption onto iron or aluminum oxides, ion exchange, or membrane processes. Remediation strategies focus on reducing exposure and removing arsenate from water and soils.