Arsenilate

Arsenilate refers to compounds containing the arsenate group, AsO4^3−, and to salts and esters derived from arsenic acid. In aqueous solution, arsenate species exist as H2AsO4− and HAsO4^2− depending on pH, with approximate pKa values near 2.2, 7.0, and 12.0. The arsenate ion is tetrahedrally coordinated around arsenic and is the pentavalent (As(V)) form of arsenic. It is a chemical analogue of phosphate and forms a wide range of metal salts and minerals.

In nature, arsenates occur as minerals such as scorodite FeAsO4·2H2O, mimetite Pb5(AsO4)3Cl, and adamite Zn2(AsO4)(OH)2. They also appear in various synthetic materials, including calcium arsenate Ca3(AsO4)2, which has been used historically as an insecticide. Arsenates can form a variety of salts with divalent and trivalent metals, and they often occur alongside other phosphate- or sulfate-bearing phases.

Uses and applications have historically included pest control and wood preservation, with calcium arsenate and lead arsenate playing prominent roles. Because of toxicity and environmental concerns, the use of arsenates is now heavily regulated or restricted in many jurisdictions. They also appear in pigments and certain ceramic or glass formulations, though such uses are carefully controlled to minimize exposure.

Safety and environmental impact are major considerations with arsenates. Arsenic compounds can interfere with biological phosphate metabolism and are toxic to humans and wildlife. In the environment, arsenates can contaminate soil and groundwater, and remediation strategies often involve adsorption, ion exchange, or oxidation to more easily remove or stabilize arsenic species.