Stabilized Nanoscale Zero-valent Iron Applied For The Remediation Of Heavy Metal Polluted River Sediment And The Study On Its Transport

With the rapid development of urban mining,electroplating industry and non-ferrous metal smelting,heavy metal polluted water is discharged into the rivers and lakes in a disorderly manner,resulting in further pollution of rivers or lakes sediments by heavy metals,among which Cd(II)pollution is particularly serious.Due to the accumulation,complexity,transferability and persistence of sediment pollution,the management of contaminated sediments poses a big challenge,contaminated sediment would pose a potential threat to human and environmental health if effective repair methods are not adopted.Therefore,the aim of this study is to seek a remediation technology for heavy metal-contaminated sediments,namely a stabilized nanoscale zero-valent iron(nZVI)environmental remediation technology,and the use of this technology is to verify the feasibility of remediation of heavy metal-contaminated river sediments,in order to further explore the field application of this technology,we also studied the transport of stabilized nZVI in porous media.In this study,sodium carboxymethyl cellulose(CMC)-stabilized nZVI(C-nZVI)and starch-stabilized nZVI(S-nZVI)were synthesized using a modified liquid-phase reduction method.By the characterization of stabilized nZVI via scanning electron microscopy(SEM),Fourier transform infrared spectrometry(FTIR),X-ray diffraction(XRD)and particle size analysis(DLS),the results showed that CMC and starch are successfully coated on the surface of nZVI,and they could effectively reduce or eliminate the surface oxidation of nZVI,inhibit the rapid agglomeration of nZVI,and maintain the high reactivity of nZVI and nanoscale size.Batch experimental data showed that when the sediment sample was treated with C-nZVI for 56 days at a dosage ranging from 5 to 10 mg/g-sediment as Fe~0,the TCLP(toxicity characteristic leaching procedure)leachability of Cd(II)in the sediment decreased by 93.75~96.43%,and the PBET(physiologically-based extraction test)bioaccessibility of Cd(II)decreased by 22.79~71.32%.Additionally,the acid soluble fraction of Cd(II)was partially transformed to a residual fraction,resulting in a32.4~33.1%decrease of acid soluble Cd(II)and a 125.4~205.6%increase of the residual-Cd(II)fraction,the migration and bioavailability of Cd(II)are effectively controlled in the sediment.At the same time,we also found that the stabilized nZVI has a stronger repair effect on the Cd(II)-contaminated sediment than the unstabilized nZVI(B-nZVI),and the repair effect is enhanced when the amount of stabilized nZVI is properly increased.The mechanism of Cd(II)immobilization in sediment by stabilized nZVI is not reduction immobilization,but it is immobilized by the strong adsorption ability of nZVI and the iron hydroxide complexation that occurs on the nZVI surface.Column experimental results showed that the stabilized nZVI(especially C-nZVI)has better mobility than B-nZVI,moreover,the maximum transport distance of stabilized nZVI in the sediment-supplemented quartz sand is significantly shorter than that in quartz sand,indicating that the physical and chemical heterogeneity of the sediment-supplemented quartz sand is still a challenge to the transport of nZVI.Overall,this study confirmed that stabilized nZVI has a good repair effect on Cd(II)-contaminated sediment,and the stabilizing agents such as CMC and starch could appropriately increase the transport distance of nZVI.