Enhanced reduction of nitrate by supported nanoscale zero-valent iron prepared in ethanol-water solution

Abstract

Nanoscale zero-valent iron is famous for its high reactivity originating from its high surface area, and has emerged as an extension of granular zero-valent iron technology. Due to its extremely small size, nanosized iron cannot be used as a medium in a permeable reactive barrier system, which is the most popular application of granular iron. To overcome this shortcoming, supported nanoscale zero-valent iron was created. In addition to this, the preparation solution was modified to enhance the reactivity. An ethanol/water solvent containing a dispersant of polyethylene glycol was used to synthesize nanoscale iron. This preparation was done in the presence of an ion-exchange resin as a supporting material. Nanoscale zero-valent iron was formed and bound to the granular resin at the same time through the borohydride reduction of an iron salt, and the resulting product was compared with that prepared in a conventional way of using water only. Switching the preparation solution increased the supported nanoscale iron's BET surface area and Fe content from 31.63 m(2) g(-1) and 18.19 mg Fe g(-1) to 38.10 m(2) g(-1) and 22.44 mg Fe g(-1), respectively. Kinetic analysis from batch tests revealed that a higher denitrification rate was achieved by the supported nanoscale zero-valent iron prepared in the modified way. The pseudo-first-order reaction constant of 0.462 h(-1) suggested that the reactivity of the supported iron, prepared in ethanol/water, increased by 61% compared with the one prepared in water. The higher rates of reaction, based on higher specific area and iron content, suggest that this new supported nanoscale iron can be used successfully for permeable reactive barriers.