Arsenite Oxidation and Arsenic Adsorption Strategy Using Developed Material from Laterite and Ferromanganese Slag: Electron Paramagnetic Resonance Spectroscopy Analysis

An oxidative catalyst has been prepared by using natural clay and industrial waste to oxidize arsenite (As(III)) and decontaminate arsenic from water. The oxidation of As(III) is necessary to increase the overall efficiency of the purification process. The raw materials were treated chemically to leach active ingredients and then precipitated as mixed metal oxyhydroxides. The study focuses on the role of active sites created by Mn oxyhydroxides and Fe or Al oxyhydroxides for the adsorption of arsenic species. Hence, the prepared catalyst can also show the As(III) species' photocatalytic oxidation in a dark environment. XANES and XPS techniques confirmed 60% oxidation of As(III) to As(V) during adsorption. Real-field arsenic adsorption was performed under the influence of various ions. It showed that the phosphate and the bicarbonate ions have a negative impact on arsenic adsorption. The adsorbent has the potential to produce nearly 30,000 bed volumes of water from arsenic-contaminated groundwater (initial arsenic concentration of 140 ± 10 μg/L). The involvement of hydroxyl free radical (HO·) in As(III) oxidation was proven through electron paramagnetic resonance (EPR) spectroscopy. The oxidative catalyst cum adsorbent has retained approximately 60% adsorption capacity after the second cycle of sorption. Thus, the adsorbent has shown much higher arsenic adsorption behavior and lower cost compared with commercial adsorbents.