Study On The Technology Of Nano-zero-valent Fe Mechanochemical Remediation Of POPs Contaminated Soil

Polychlorinated biphenyls and polybrominated diphenyl ethers have been widely used in various industries due to their good chemical properties.Dismantling of E-waste,which contains many high economic value metals,can bring considerable economic benefits.In the process of dismantling,due to backward technology and imperfect systems,many small and medium-sized retail households will flow the POPs(PCBs、PBDEs)in the E-waste into the surrounding medium where they are located,causing serious threats to the safety and health of human life and the surrounding ecological environment.This subject takes PCBs and PBDEs contaminated soil as the research object,and uses mechanochemical methods to degrade POPs in the soil to achieve the purpose of remediation of the contaminated soil.The main research contents include:(1)Explore the influence of mechanochemical process conditions on the degradation effect of PBDEs.The experimental results show that when the ball milling time is 4 h,the ball milling speed is 550 rpm,the ball-to-battery(BPR)is 14:1,and the addition amount of nano-zerovalent iron and oxide is 10 %,the concentration of BDE209 in the soil can be reduced from 200.52 mg/kg to 4.17 mg/kg,which degradation rate can reach 97.92%.(2)Explore the influence of mechanochemical process conditions on the degradation effect of PCBs.The experimental results show that when the ball milling time is 4 h,the ball milling speed is 550 rpm,the ball-to-battery(BPR)is 14:1,and the addition amount of nano-zerovalent iron and oxide is 10 %,PCBs in the soil can be degraded in a large amount.The degradation rate of tetrachlorobiphenyl and pentachlorobiphenyl can reach more than 99%.(3)Study on the reaction kinetics of POPs degradation by mechanochemical method.The experimental results show that the mechanochemical reaction rate constant has a certain linear relationship with the milling time,the milling speed and the BPR.(4)This study used GC-MS to test the intermediate and final products before and after ball milling to explore the mechanism of mechanochemical degradation of POPs in soil.The results show that the mechanochemical method can degrade high-brominated compounds to produce low-brominated compounds,and with the increase of time,these compounds will eventually be completely degraded to produce non-toxic small molecule compounds.(5)In this study,the surface of the ball milled product was characterized by scanning electron microscope,element analyzer,particle size analysis,and XRD.The results show that C and Br are formed in the ball milled product,the particle size of the sample is larger than that of the sample without ball milled,and a new diffraction peak appears in the XRD characterization.