Factors and mechanisms controlling bromate removal by zerovalent iron.

摘要

The zerovalent iron (Fe(0)) technology widely used in remediating contaminated groundwater can be applied to drinking water treatment for reduction of bromate, a refractory by-product produced during ozone disinfection. Bromate reduction by Fe(0) under various conditions was investigated in batch tests to study the effects of iron properties (size and surface properties), repeated uses of iron, mixing rates, bromate/iron weight ratios, pH, DO, temperature, common anions and natural organic matter (NOM) on the reduction kinetics. Bromate can be completely reduced to bromide ions with good fit to pseudo-first-order kinetics and the reduction rate is considerably affected by the parameters studied. The results indicate that bromate reduction in aqueous solution is a surface-mediated chemical reduction reaction. This reaction is predominantly controlled by the iron surface conditions, although diffusion to iron surface is essential.; The role of humic acid in bromate reduction by Fe(0) was further examined in the study. The reduced functional groups present in humic acid were observed to regenerate Fe(II) and reduce bromate abiotically. The electron spin resonance further demonstrated that the redox functional groups in humic acid are most likely quinone-phenol moieties.; The growth of films of iron precipitates may affect chemical reduction of bromate by Fe(0) through the change of the interfacial properties. X-ray photoelectron spectroscopy, time-of-flight secondary mass ion spectrometry, micro-raman spectroscopy and scanning electron microscope-energy dispersive analysis of X-ray were utilized in this study to characterize the property of the film. These microscopic observations and the enhanced bromate reduction with addition of Fe(II) form a model to describe the bromate reduction with the presence of iron precipitates.; Bromate reduction by Fe(0) with incorporation of copper or palladium was investigated in batch tests. The enhanced bromate reduction rate in the presence of copper observed here is the result of the newly formed active Cu(I). The presence of PdO was evidenced by XPS but it possibly counter-balanced the reduction in adsorption and thereby yielded no enhancement in bromate reduction. Finally, the Cu2O present on the iron surface because of copper impurities in commercially available iron was found to be involved in the bromate reduction and to accelerate the reduction rate.