Effect of boron on reactivity and apparent corrosion rate of microscale zerovalent irons

Abstract

The reactivity and apparent corrosion rate of newly produced boron-alloyed microscale zerovalent iron (mZVI) particles toward a variety of chlorinated aliphatic hydrocarbons (CAHs) were assessed in laboratory-scale batch reactors. For comparison, commercially available nanoscale zerovalent irons (nZVIs) were also included in the study. Based on mass normalized (kM) pseudo first-order degradation rate constants, the reactivity of boron-alloyed mZVIs appeared to be one order of magnitude lower than most reactive nZVI. However, specific surface area normalized reaction rate constants (kSA) were 1–2 orders of magnitude higher than for nZVIs showing that boron-alloyed mZVIs can compete with nZVIs. The high reactivity of boron-alloyed mZVIs was attributed to (1) the prevented iron surface passivation during anaerobic corrosion due to the simultaneous iron and boron dissolution kinetics preventing the formation of insoluble oxidized iron species, (2) the involvement of boron in facilitating electron transfer by inducing β-elimination followed by hydrogenation to ethane and/or (3) involvement of boron in improved particle size reduction during milling process leading to increased active surface areas of the particles. Results of this study suggest that boron-alloyed mZVIs could be an efficient alternative to nZVIs for in situ groundwater remediation of different CAHs in terms of their reactivity and apparent corrosion rate.