Degradation Of Decabromodiphenyl Ether In The Soil Of Ewaste Dismantling Site By Activating Persulfate Using Kaolin Supported Sulfide-Modified Nanoscale Zero-Valent Iron

Decabromodiphenyl ether?BDE209?is the main organic pollutant in the soil of electronic and electric waste?e-waste?dismantling site.BDE209 entering in the soil is difficult to be degraded,which seriously threatens the local environmental security and human health.The mineralization of BDE209 can be achieved by nanoscale zero-valent iron?nZVI?combined chemical oxidation technology,which can avoid secondary pollution caused by incomplete degradation.In this paper,kaolin supported sulfide-modified nanoscale zero-valent iron?K@S-nZVI?was synthesized via liquid phase reduction method and was used as a kind of activator of persulfate?PS?to degrade BDE209 in the soil.The reaction conditions were optimized and the degradation mechanism was explored in this study.The main research results are shown as follows:?1?K@S-nZVI was synthesized and characterized using SEM,XRD and XPS.SEM results showed that sulfide-modified nanoscale zero-valent iron particles were uniformly attached to the surface of flaked kaolin.The surface of sulfide-modified nanoscale zero-valent iron particles was wrinkled.Results of XRD and XPS analysis showed that the surface of K@S-nZVI contained zero-valent iron,iron oxides,iron hydroxides and iron sulfides,which proved that zero-valent iron was successfully sulfide-modified.?2?Compared with the traditional nanoscale zero-valent iron and sulfide-modified nanoscale zero-valent iron,the degradation efficiency of BDE209 was the best when K@S-nZVI acted as activator of PS oxidation system.Because the presence of carrier and covered agent,K@S-nZVI had better dispersity and was not easy to be oxidized and agglomerated,thus it could keep stable for a long time.?3?The effect of the molar ratio of S/Fe,the concentration of PS,the dosage of K@S-nZVI,pH value and temperature on the degradation of BDE209were investigated in this study.Results showed that the degradation efficiency of BDE209 would be inhibited if the degree of sulfuration was too high or too low;excessive addition of K@S-nZVI would also decrease the degradation efficiency;the removal efficiency of BDE209 increased with the concentration of PS and temperature increased;acid condition would promote the degradation process,however,alkalin environment would inhibit the degradation of BDE209.When the molar ratio of S/Fe was 1:4,the concentration of PS was 0.2 mol/L,the molar ratio of PS/K@S-nZVI was 2:1,pH value was 3 and the reaction temperature was 313 K,88.32%of BDE209 in the soil was removed using K@S-nZVI/PS oxidation system.The degradation process fitted to the pseudo-first-order kinetic model well.The reaction rate constant(k_obs)and the reaction temperature fitted to Arrhenius formula,and the reaction activation energy was 52.4 kJ/mol.?4?SO₄^-·and HO·were found in this system.Under acidic conditions,SO₄^-·was the dominated radical species.Under neutral conditions,both SO₄^-·and HO·contributed to the degradation reaction.Under alkaline conditions,HO·contributed more to the degradation reaction of BDE209.?5?During the degradation of BDE209 in the soil by K@S-nZVI/PS system,the concentration of PS decreased gradually,finally,about 16%of PS remained in the soil after reaction.?6?Debrominated intermediates of BDE209 using K@S-nZVI system included BDE207,BDE206,BDE203,BDE196,BDE190,BDE183,BDE154,BDE153,BDE119,BDE99,BDE66,BDE47,BDE28,BDE17 and BDE7,indicating that the degradation of BDE209 by this system is a gradual debromination process.Radicals then participated in the substitution reaction and attacked the ether bond and benzene ring of the low brominated biphenyl ether,eventually BDE209 was degraded into carbon dioxide,water and short chain carboxylic acid.