Of the two predominant forms of arsenic in water, arsenate and arsenite, most treatment processes are effective at removing arsenate, but not arsenite, since arsenite is typically non-charged below pH 9.2. Therefore, treatment for the removal of arsenic often includes an oxidation step to convert arsenite to arsenate.
Oxidation can be simply the addition of oxygen to a compound, or more generally, any reaction involving the loss of electrons from an atom. Aeration, the supplying
of air, oxidizes arsenic, converting arsenite to arsenate, and the iron that co-occurs. This is precipitated as FeAsO4. Arsenic can also be oxidized by a number of other chemicals including chlorine, hypochlorite, ozone, permanganate, hydrogen peroxide and Fenton’s reagent (H2O2/Fe2+). Photochemical oxidization proceeds from the reaction of radiant energy and a chemical system.
Oxidation alone does not remove arsenic from solution but must be combined with an arsenic removal process.