Effect and mechanism of Fe-Mn oxides and clay minerals on abiotic natural attenuation of normal alkanes
Soil constitutions,especially iron oxides,manganese oxides and clay minerals(FeMn-Clay minerals,FM-C),exert a distinguished role in the transformation of organic contaminants.However,the contribution of FM-C to abiotic natural attenuation of normal alkanes in the dark has long been overlooked.In this study,a sterile ex-periment was conducted to examine the effects of different contents(1％,2％,3％)of iron oxides(Fe3O4,Fe2O3 and FeO(OH)),manganese oxides(MnO2)and clay minerals(kaolinite and montmorillonite)on the degradation of normal alkanes(long-chain C16-C31).The results showed that 3％FM-C possessed the highest transformation rate for normal alkanes,with a transformation rate up to 52.79％in 63 h.X-ray photoelectron spectroscopy(XPS)characterization suggested that Fe(Ⅱ)had the strongest effect,which was conducive to directly convert O2 into superoxide radical(O2·-).FM-C had the higher oxygen vacancy concentration,providing sufficient adsorbed oxy-gen that was stimulative for transformation and degradation of normal alkanes.The O2·-signal before and after the reaction was detected by electron paramagnetic resonance(EPR).The results confirmed that the transformation of normal alkanes was accompanied by O2·-.FTIR characterizations showed that the abiotic natural attenuation of nor-mal alkanes was accompanied by forming new functional groups(C-OH).Consequently,the promoting effects of FM-C on abiotic degradation of normal alkanes and the possible pathways were concluded.Our results provided val-uable insights into the abiotic natural attenuation of normal alkanes by inorganic minerals in soils under dark condi-tions.
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