Kinetics for Metallic Iron Corrosion and Hexavalent Chromium Reduction

Abstract

Corrosion kinetics of Fe⁰ in aqueous at pH 2 is controlled by the transport step of productsfrom redox reaction through a liquid film layer from iron surface to bulk solution which can berepresented by the following equation:

d[Fe²⁺]/dt= 5.9 x [Area] x t ^-(1/2)

where "d[Fe2+]/dt" is in mg.l^-1.min^-1, "[Area]" is surface area concentration of Fe⁰ in m².l^-1, "t"is time in min, and the rate constant in mg.m^-2.min^-0.5. The redox reaction of Fe⁰ with Cr(VI) is morerapid than that with water and is the first order with respect to Cr(VI) and Fe0 surface areaconcentrations; hence, the second order overall as follows:

d[Cr(VI)]/dt= -0.0018 x [Area] x [Cr(VI)]

where "d[Cr(VI)]/dt" is in mg.l^-1min^-1, "[Cr(VI)]" is in mg.l^-1, and the rate constant inl.m^-2.min^-1. The results from Goodness of Fit Test show that there is no significant lack of fit at 95% confidence for both rate equations obtained in this study.

Keywords : Zero-valent Iron / Hexavalent Chromium / Corrosion / Reduction / Redox Reaction