Degradation Of Polychlorinated Biphenyls In Soils By Zero Valent Iron

Polychlorinated Biphenyls(PCBs)in soil as study object and three kinds of zero-valent iron(nanoscale zero-valent iron,nickel iron bimetal and micron zero-valent iron)are used as reducing agents to research the degradation characteristics and mechanism of PCBs in single polluted soil and composite contaminated soil.The experimental results showed that the three types of zero-valent iron had obvious effects on the degradation of PCB138 in soil.The results of kinetic analysis indicated that the degradation reaction of PCB138 in soil conformed to the first-order reaction kinetics.The reaction rate constants of nanoscale zero-valent iron,nickel iron bimetal and micron zero-valent iron were 0.01546 h-1,0.01937 h-1 and 0.00989 h-1,respectively.Under the experimental conditions,the degradation rate of PCB138 in soil increased with the increase of the dosage of the zero-valent iron.The lower the initial pH value of the reaction system,the better the effect of three kinds of zero-valent iron on the degradation of PCB138 in soil.The increase of temperature had little effect on the degradation of PCB138 under the experimental condition of 20～50℃.The determination result of Fe2+ concentration showed that the concentration of Fe2+ was increased with the decrease of pH under acidic conditions.Under the same condition of pH,the concentration of Fe2+ in the supernatant of three types of zero-valent iron increased with the increase of time.The degradation process of Humic acid PCB138 in three kinds of zero-valent iron was also consistent with the first-order kinetic equation,and the degradation rate of PCB138 in Humic acid was obviously higher than that in native soil.In Humin,the degradation rate of PCB138 in the zero valent iron system was lower than that of Humic acid.The degradation of seven kinds of PCBs in complex contaminated soils showed that the degradation process of seven kinds of PCBs accorded,with the first-order reaction kinetics.QSPR analysis showed that the main factors affecting the soil degradation of PCBs under the experimental conditions were Elumo,Ehomo and Smθ.