COMPARISON OF THE REACTIVITY OF NANOSIZED ZERO-VALENT IRON (nZVI) PARTICLES PRODUCED BY BOROHYDRIDE AND DITHIONITE REDUCTION OF IRON SALTS

Abstract

Dithionite can be used to reduce Fe (II) and produce nanoscale zero-valent iron (nZVI) under conditions of high pH and in the absence of oxygen. The nZVI is coprecipitated with a sulfite hydrate in a thin platelet. The nanoparticles formed are not pure iron but this feature does not appear to affect their degradation performance under air or N 2 gas conditions. The efficiency of trichloroethylene (TCE) degradation, when one is employing nanoparticles manufactured using dithionite ( nZVI S 2 O 4 ), is similar to if not slightly better than that of the more conventional borohydride procedure ( nZVI BH 4 ). The other advantages of the dithionite method are that (i) it uses a less expensive and widely available reducing agent, and (ii) there is no production of potentially explosive hydrogen gas. Oxidation of benzoic acid using the nZVI S 2 O 4 particles results in different byproducts than those produced when nZVI BH 4 particles are used. The low oxidant yield based on hydroxybenzoic acid generation is offset by the production of higher concentrations of phenol. The high concentration of phenol compared to hydroxybenzoic acids suggests that OH • addition is not the primary oxidation pathway when one is using the nZVI S 2 O 4 particles. It is proposed that sulfate radicals ([Formula: see text]) are produced as a result of hydroxyl radical attack on the sulfite matrix surrounding the nZVI S 2 O 4 particles, with these radicals oxidizing benzoic acid via electron transfer reactions rather than addition reactions.