The Degradation Of PCBs In Soils By Zero-valent Metallic Mixed Powder

Polychlorinated biphenyl (PCB) is the most typical kind of 12 types of persistent organic pollutants (POPs) that people have always been paying attention to. Remediation of PCB-contaminated soil has been one of the hotspot researches for its extremely stable physical-chemical property. This paper has investigated the effect of zero-valent metallic mixed powder by iron and magnesium for repairing PCB-contaminated soils and has obtained good results. The main researches of the paper were as follows.1. Investigating the degradation effect of PCB-contaminated soils by metallic mixed powder composed of iron and magnesium and reaction parameters that may have influences on removal efficiency. Removal rate of PCBs can be up to 98.10% in 24h under the conditions of Fe-Mg ration was 2:3 and power-soil ratio (wt%) was 1:500, in room with room temperature (20℃). The influences by electrolyte solution, reaction time, direct sunlight and temperature on the effect of remediation have also been studied. According to the experimental results, it can be seen that removal rate was increasing with the extension of reaction time and it could be up to 98% in 24h; addition of extra electrolyte solution could lead to better remediation effect in the same reaction time; direct sunlight has been proved to be helpful in the degradation process, especially in the first 6-8h; raising temperature was adverse to the degradation effect when temperature was ranging from 20℃to 50℃, it could get the highest removal rate 96.32% as temperature was controlled to 20℃. Ratio of Fe-Mg was ranging from 0.2-0.67 without any obvious change of removal efficiency, when it was raised from 0.67-1, removal rate has decreased and was 93.29% as the ratio was 1.2. Investigating the mechanism of degradation. Result has indicated that two products were found after degradation process of PCBs, one was para-cymene, the other was trimethylsilyl 2,6-bis (trimethylsilyloxy) benzoate, toxicity of both were less than polychlorinated biphenyls.Researches above demonstrated that zero-valent metallic mixed powder by iron and magnesium is an effective technique for remediation of PCB-contaminated soils and that, it provides a reference for remediation of PCB-contaminated soils in future.