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The oxidation method includes the use of an oxidizing agent (Cl₂, ClO₂, O₃, H₂O₂, NH₂Cl, MnO₄⁻, FeO₄²⁻, etc.) to eliminate heavy metals from water (Sharma et al. 2007; Mondal et al. 2013; Bora and Dutta 2019). Investigation of the photochemical and photocatalytic oxidation process includes the oxidation of heavy metals using UV radiation, O₂, etc. for the removal of dissolved pollutants. UV/solar radiation assists to develop the hydroxyl radicals during the photolysis of iron and iron hydroxide (fe(OH)₃), hydroxyl radicals and O₂ oxidizes the toxic metals like As(III) to As(V). The presence of these radicals, the oxidation reaction becomes faster (Yoon and Lee 2005; Sharma et al. 2007). On the other hand, the photocatalytic reaction is carried out in the presence of TiO₂ for oxidation of the heavy metals (Miller et al. 2011).

Figure 4.2 Schematic of conventional different conventional methods to decontaminate water from heavy metals.