SIMULTANEOUS REMOVAL OF ARSENIC AND OTHER INORGANIC AND ORGANIC CONTAMINANTS USING ELECTROCHEMICAL PEROXIDATION

The nearly complete (99.2-99.7%) sorption of arsenic to hydrous ferric oxides (HFOs) has been observed during electrochemical peroxidation experiments. Electrochemical peroxidation utilizes dilute concentrations of hydrogen peroxide, small amounts of direct current, and sacrificial steel electrodes to create hydroxyl radicals. Originally developed to oxidize aqueous phase organic contaminants, sparingly soluble hydrous ferric oxides (HFOs) are formed as a byproduct of the induced Fenton's Reagent reactions and can easily be recovered. The sorption of metals by HFOs is widely reported and can serve as an effective removal strategy from aqueous solutions. A series of experiments utilizing multi-element (As, Be, Cd, Cr, Cs,Cu, Li, Ni, Pb, Se, V, and Zn) stock solution (2.5 mg/L per element) was conducted in which the effects of pH (3.5, 4.5, 6.5) , presence or absence of current (3 or 6 minutes @ 0.25a DC), and presence or absence of H2O2 (100 or 1000 mg/L) were optimized. At pH 3.5, and in the presence of H2O2, nearly complete (>90%) sorption of As and Cr, and strong (70-90%) sorption of Pb, Se, and V was observed. At near neutral pH (6.5) and in the presence of H2O2, nearly complete (>90%) sorption of As, Cr, and Pb, and strong (70-90%) sorption of Be, Cu and Se was observed. Without current application only Pb (99.4%) was effectively removed at pH 4.5 and 6.5. Only Cd, Cs, Li, and Ni were not strongly adsorbed in any experimental scenario. Little or no benefit was found when current duration or peroxide concentration was increased above three minutes and 100 mg/L, respectively. The use of peroxide additions enhanced Arsenic recovery from 79.2 to 99.2% due to the oxidation of As (III) to As (V) and As (V)'s stronger affinity for HFO. In a series of separate experiments, aqueous phase polychlorinated biphenyls (PCBs) were oxidized (>95 %) and also adsorbed (>99%) to HFOs, suggesting the possibility of treating mixed organic and inorganic waste through oxidation of organic compounds and sorption and removal of metals.