Efficiency And Mechanisms Of Surface-modified Nanoscale Zero-valent Iron For The Removal Of Organic Pollutants In Different Reaction Systems

Nanoscale zero-valent iron(NZVI)has shown great potential in groundwater pollution due to its large specific surface area and high reactivity.However,in addition to these advantages,there are still some limitations in its practical applications,such as tendency to agglomeration and sedimentation,and inactivation by passivation.To solve the problems above,the essay uses different stabilizers to modify NZVI and sulfidated NZVI to study the removal efficiency of pollutants by surface modified NZVI in oxidation and reduction system.In oxidation system: starch,sodium dodecylbenzene sulfonate(SDBS)and carboxymethyl cellulose(CMC)modified NZVI(STARCH/NZVI,CMC/NZVI,SDBS/NZVI)were applied to activated persulfate and degrade sulfamethazine(SMT).This study investigated the effects of stabilizer/NZVI mass ratio,p H,groundwater composition(such as calcium ions,bicarbonate ions,sulfate and humic acid)and particle aging on the removal of SMT.The results show that,compared with the pristine NZVI,the modified NZVI shows a higher SMT removal rate.The removal rate of SMT in simulated groundwater is significantly reduced,especially at pH 9,which may be due to the free radical scavenging effect of the groundwater components(such as bicharbonate and humic acid)and the buffering effect of bicarbonate.After 15 days of aging in air,the pristine NZVI and surface-modified NZVI can still completely remove SMT within 1h.XRD analysis reflects that neither the pristine NZVI nor the modified NZVI is significantly oxidized in the air,and can still be used for the activation of persulfate.In reduction system: study the colloidal stability of starch,SDBS and CMC-modified SNZVI(STARCH/SNZVI,SDBS/SNZVI,CMC/SNZVI)and its ability to remove trichloroethylene(TCE)were studied.All three types of stabilizers can enhance the colloidal stability of SNZVI,but show different removal effects on trichloroethylene(TCE).STARCH/SNZVI has the best removal efficiency,which is attributed to the increased stability of the colloids to provide more active surface sites.However,although SDBS and CMC can also enhance the colloidal stability of SNZVI,it inhibits the removal of TCE.This may be due to SDBS/CMC occupying the active site of SNZVI surface for the removal of TCE.In addition,the effects of p H,calcium ions,and humic acid on TCE removal were also studied.With increasing p H(from 5to 9),the TCE removal efficiency of all modified SNZVI decreased slightly.Calcium ions and humic acid have no significant effect on the reactivity of CMC/SNZVI,but significantly reduce the reactivity of STARCH/SNZVI and SDBS/SNZVI.This is because there are different interactions between the calcium ions,humic acid and the three stabilizers on the SNZVI surface.