Interaction Between The Corrosion Behavior Of Sulfidated Nanoscale Zerovalent Iron And Its Efficiency For Cr（Ⅵ） Removal From Oxic Water

Nanoscale zerovalent iron（nZVI）,a versatile material with uniquely aquatic surface chemistry properties,has been extensively applied for the remediation of groundwater and treatment of wastewater.When decontamination,nevertheless,most of electrons donated by nZVI are consumed by the side reactions with O2,and H2O/H+under aerobic condition.Therefore,the invalidation of nZVI due to the corrosion has been a crucial issue and thus its improvement is of great significance.Although it has been reported that the sulfidation can suppress the side reaction with water under anaerobic conditions and thus improve the efficiency of nZVI toward target contaminants,the influence of sulfidation on reduction efficacy of nZVI toward targets over with nontargets under different aeration systems keeps unknown.To address this issue,Cr（Ⅵ）was selected as the target pollutant in this study to explore the interaction mechanism between Cr（Ⅵ）removal efficiency and corrosion behaviors of sulfidated nZVI（S-nZVI）under oxic water.（S-nZVIone）Firstly,the removal efficiency of Cr（Ⅵ）by S-nZVI under different aeration systems was investigated.With promoting the S/Fe molar ratio,the removal rate of Cr（Ⅵ）by S-nZVI was initially increasing but then decreasing.Especially when the molar ratio of S/Fe was 0.16,the optimized removal rate of Cr（Ⅵ）by one-step S-nZVI（i.e.,S-nZVIone）in the absence of oxygen could reach 0.7910 min-1,which induced the4.59-time（greater than with nZVI）.Based on this optimal S/Fe molar ratio（i.e.,0.16）,it was further proved that the removal rates of Cr（Ⅵ）by S-nZVIone and S-nZVItwo（i.e.,two-step S-nZVI）under different solution chemistry（including p Hini,cations and anions）were increased by 1.63-6.11 and 1.44-2.68 times than that by nZVI,respectively.Collectively,the reactivity of S-nZVIone toward Cr（Ⅵ）shows higher than that of twostep S-nZVI（S-nZVItwo）under different water-oxygen atmospheres.Secondly,based on the thermodynamic analysis,the electron transfer of Fe Sx in the process of Cr（Ⅵ）removal by S-nZVI were clarified in this study.To explore the system mechanism,this study further clarified the in-siu corrosion behavior of SnZVIone under different water-oxygen atmospheres monitored by electrochemical techniques,involving kinetics of Tafel and open circuit chronopotentiograms.By correlation analysis,it was further found that the rate constant of Cr（Ⅵ）removal in the anaerobic system was correlated with the polarization resistance Rp and and corrosion potential Ecorr.to some extent,and the correlation coefficient increases gradually with the reaction time,largely implying that the removal of Cr（Ⅵ）was mainly dependent on the reduction of S-nZVIone as the electron transfer process of Cr（Ⅵ）removal was dominant.Moreover,it was further found that k Cr JMAK and k Cr log were negatively correlated with the exponential rate constant k JMAK at the initial stage of open potential and the logarithmic rate constant klog at the later stage of open circuit chronopotentiograms in anaerobic and aerobic systems,respectively,which confirmed that sulfidation can improve the Cr（Ⅵ）removal efficiency of nZVI by improving the mass and electron transfer at the initial and later stage of the reaction system,respectively.In general,this study will provide novel exploring perspective and solid theoretical support for the efficient utilization of nZVI-based technology in real environmental application.