Removal Of Polychlorinated Biphenyls-heavy Metals Co-contamination By Modified Nanoscale Zero-valent Iron

With the rapid consumption of electronic products,e-waste has become an urgent global environmental issue.Traditional e-waste dismantling activities have brought huge profits and caused lots of pollution to the environment.Among them,the polychlorinated biphenyls?PCBs?-heavy metals co-contamination is the most serious problem,but there are few studies on the remediation of this problem all over the word.As green and economical materials,nanoscale zero-valent iron?nZVI?and its modified materials can simultaneously remove PCBs and heavy metals.In this paper,2,2',4,4'5,5'-hexachlorobiphenyl?PCB153?,Cu²⁺ and Ni²⁺ were selected as the target pollutants.The removal efficiencies of nZVI,sulfidated nanoscale zero-valent iron?S-nZVI?and carboxymethylcellulose stabilized nanoscale zero-valent iron?CMC-nZVI?on PCBs,heavy metals and PCBs-heavy metals co-contamination were investigated seperately.The effects of pH,anion and humic acid on the removal of two types of pollutants were studied.The interaction between PCBs and heavy metals in the combined pollution system was discussed.The reaction mechanism and influence mechanism were also explored.The main conclusions are as follows:?1?Three types of nanoscale zero-valent iron were prepared:nZVI and CMC-nZVI were prepared by liquid-phase reduction method(CMC concentration was 1.00 g·L^-1),and S-nZVI was prepared by one-step synthesis method?S/Fe ratio was 0.103?.The crystal structure of three materials was ?-Fe⁰.The particle size of S-nZVI was slightly larger than that of nZVI and CMC-nZVI.The surface layer of S-nZVI was iron oxide and iron sulfide,and that of nZVI and CMC-nZVI was iron oxide.?2?The reactivity of the degradation of PCB153 decreased in the order of CMC-nZVI>nZVI?S-nZVI.The pseudo-first-order kinetic constants?kobs?were 0.016,0.006 and 0.005 h-1,respectively.The degradation mechanism was hydrogenolysis,and the product was tetrachlorobiphenyl.The low reactivity of S-nZVI to PCB153 may be due to the consumption of Fe⁰ by the production of iron sulfide,while the high reactivity of CMC-nZVI may be related to the dispersion of CMC.Low pH conditions favored the degradation of PCB153 by nZVI and CMC-nZVI,while S-nZVI was the opposite.NO3-and humic acid inhibited the degradation of PCB153 by three materials,while Cl-promoted the degradation of PCB153.?3?The reactivity of the removal of Cu²⁺ decreased in the order of CMC-nZVI>S-nZVI>nZVI and the kobs were 2.890,1.919 and 1.384 min-1,respectively.The removal mechanism of Cu²⁺ was reduction.MTIe reactivity of the removal of Ni²⁺ decreased in the order of S-nZVI>CMC-nZVI>nZVI and the kobs were 0.931,0.360 and 0.304 min-1,respectively.The removal mechanism of Ni²⁺ was adsorption and reduction.The optimum pH values for Cul?and Ni²⁺ removal by three materials were 5 and 6,respectively.The effects of anion and humic acid on the removal of Cu²⁺ and Ni²⁺ were similar with those of PCB153.The removal rate of Cu²⁺ by three materials was higher than that of Ni²⁺,but it was more susceptible to the above factors.?4?In PCBs-heavy metals combined pollution system,PCB153 had little effect on the removal of Cu²⁺ and Ni²⁺ by three materials.PCB153 did not hinder the electron transfer between nanoscale zero-valent iron and heavy metals.Cu²⁺ promoted the degradation of PCB153 by nZVI and inhibited the degradation of PCB153 by S-nZVI and CMC-nZVI.Ni²⁺ promoted the degradation of PCB153 by three materials.XPS and electrochemical analysis showed that the effects of Cu²⁺ and Ni²⁺ on the dechlorination of different materials might be related to the deposition of CuU and Ni0 on the surface of nanoscale zero-valent iron and the change of electron transfer ability.In summary,three materials had different removal effects on PCBs,heavy metals and PCBs-heavy metals co-contamination.For PCB153 and Cu²⁺,the reactivity of CMC-nZVI was higher;for Ni²⁺,S-nZVI was higher;for PCBs-heavy metals co-contamination,the reactivity of CMC-nZVI was higher.PCBs had little effect on the removal of heavy metals by nanoscale zero-valent iron,while heavy metals had a certain effect on the degradation of PCBs.This study provides a theoretical basis for the remediation of PCBs-heavy metals co-contamination by nanoscale zero-valent iron.