Reduced nontronite-activated H2O2 for contaminants degradation: The beneficial role of clayed fractions in ISCO treatments.

Clayed fractions in aquifers are generally deemed to be detrimental for in situ chemical oxidation (ISCO) treatments due to the difficulty of oxidant injection/transport and the retention/rebound of contaminants. Using a model clay mineral nontronite and a real sediment, here we show that the component of structural Fe(II) in clay minerals is particularly effective in activating hydrogen peroxide (H2O2) to hydroxyl radicals (OH) for contaminants degradation under pH-neutral conditions. Using reduced nontronite (Fe(II)/Fetotal : 40 %) as a model Fe(II)-bearing clay mineral, 2 mg/L trichloroethylene (TCE) was degraded by 82.0 % and 95.3 %at 2.5 min and 30 min, respectively, under the condition of 0.6 g/L reduced nontronite, 0.5 mM H2O2and pH 7.5. Reactive structural Fe(II) in nontronite was responsible for the initial quick reaction. The degradation was also efficient for phenol, benzoic, toluene and naphthalene, but exhibited higher efficiencies for those with stronger sorption to nontronite. With similar concentrations of H2O2 and Fe(II), nontronite-activated H2O2 at pH 7.5 led to similar efficiencies of TCE degradation and H2O2 utilization to classic homogeneous Fenton at pH 3. A real clayed sediment showed similar performance in activating H2O2 for contaminant degradation. Our findings implicate that clayed fractions in aquifers may probably contribute to contaminants degradation in H2O2-based ISCO treatments.