| Abstract
| - Batch experiments were performed to investigate thefeasibility of humic acid (HA) removal by synthetic nanoscalezerovalent iron (NZVI) and its interaction with As(III) andAs(V), the most poisonous and abundant of groundwaterpollutants. High-resolution transmission electron microscopy(HR-TEM) and X-ray diffraction (XRD) were used tocharacterize the particle size, surface morphology of thepristine NZVI and HA-treated NZVI (NZVI-HA), and the zerovalence state of the pristine NZVI. It was determinedthat HA was completely removed by NZVI (0.3 g/L) withina few minutes, at a wide range of initial pH values (∼3.0−12.0). Fourier transform infrared (FTIR) and laser light scattering(zeta potential measurement) studies confirmed that NZVI-HA forms inner-sphere surface complexation at differentinitial pH conditions. The effects of competing anions showedthat there was complete removal of HA in the presenceof 10 mM NO3- and SO42- whereas HA removal was observed0%, 18% and 22% in presence of 10 mM H2PO42-, HCO3-and H4SiO40, respectively. However, the presence of 2 mMCa2+ and Mg2+ enhanced HA removal from 17 mg g-1 to76 mg g-1 and 55 mg g-1, respectively. Long-term time-resolvedstudies of XRD and field emission scanning electronmicroscopy (FE-SEM) with energy-dispersive X-ray (EDX)revealed the formation of various types of new iron oxides(magnetite, maghemite, and lepidocrocites) during thecontinuous reaction of HA in the presence of water andNZVI at 1, 30, 60, and 90 days. In addition, the surface-area-normalized rate constant (ksa) of adsorption of As(III)and As(V) onto NZVI was reduced in the presence of HA(20 mg L-1), from 100% to 43% and 68%, respectively.Our results show the potential use of NZVI in removingHA and its possible effects on arsenic removal during theapplication of NZVI in groundwater remediation.
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