Hydrogen peroxide decomposition in bicarbonate solution catalyzed by ferric citrate*This article has a companion paper in this issue (doi: 10.1139/v11-080).

Abstract

The peroxymonocarbonate mono- and di-anions (HCO4–and CO42–) are known to be generated from H2O2/HCO3–. They are promising oxidants for wood pulp bleaching, but peroxide decomposition catalyzed by ferric complexes can be significant for pulps whose lignin is highly reactive. Dicarboxylates from lignin peroxidation are believed to be the ferric chelators in the pH 8.5 range that is optimum for H2O2/HCO3–. This investigation aimed to see if HCO3–addition caused destabilization of the peroxygen system owing to its partial conversion to HCO4–. This anionic peracid is a much stronger oxidant than H2O2and could lead to a higher rate of Fe(II) oxidation to Fe(III) and (or) Fe(IV). For most free radical chain mechanisms, an increase in Fe(II) oxidation results in a higher rate of peroxide decomposition. Based on the kinetic data that were obtained and theoretical analyses, it was concluded that HCO4–did not significantly destabilize the peroxygen system when citrate was used as a model chelator for Fe(III). Increasing the [HCO3–] fourfold from 0.025 to 0.10 mol/L caused the decomposition rate to increase by only 20%.