Understanding of effect of the surface modifiers that are used for mobility enhancement of nanoscale zero-valetn iron (NZVI) on the reactivity and degradation capacity is important for successful application of the NZVI to groundwater remediation. Effects of anions (NO3-, HCO3-, Cl-, SO42-) and humic acid on the reactivity and core/shell chemistries of organically modified, i.e., polyacrylic acid-coated nanoscale zero-valent iron (PAA-NZVI) and inorganically modified NZVI (INORG-NZVI) particles were investigated. The reactivity tests at various ion concentrations (0.2 ~ 30 mN) revealed the existence of a favorable molar ratio of anion/NZVI that increased the reactivity of NZVI particles. The presence of a relatively small amount of humic acid (0.5 mg/L) substantially decreased the INORG-NZVI reactivity by 76%, whereas the reactivity of PAA-NZVI decreased only by 12%. The XRD and TEM results supported the role of the PAA coating of PAA-NZVI in impeding the oxidation of the Fe(0) core by groundwater solutes. This protective role provided by the organic coating also resulted in a 2.3-fold increase in the trichloroethylene (TCE) reduction capacitiy of PAA-NZVI compared to that of INORG-NZVI in the presence of anions/humic acid. Ethylene and ethane were simultaneously produced as the major reduction products of TCE in both NZVI systems, suggesting that a hydrodechlorination occurred in the absence of metallic catalysts. The PAA coating, originally designed to improve the mobility of NZVI, enhanced TCE degradation performances of NZVI in the presence of anions and humic acid.

Effect of groundwater solutes on the performance of nanoscale zero-valent iron particles coated with polyacrylic acid

248th National Meeting (2014)

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