Decomposition of hydrogen peroxide by manganese in the presence of lignin

In this study, the effects of both free manganese ions and manganese in the presence of precipitated lignin on the decomposition of hydrogen peroxide under typical pulp bleaching conditions were investigated. Precipitated lignin was generated by hydrochloric acid, without further purification, and reacted with a Mn solution before testing its effect on peroxide decomposition. A variety of bleaching stabilizers, ethylenediaminetetraacetic acid (EDTA), sodium silicate (Na2SiO3) and magnesium sulfate (MgSO4), were added individually or in combination, to investigate their effects in controlling the free manganese induced or precipitated lignin-combined manganese induced hydrogen peroxide decomposition. Fourier Transform Infrared Spectroscopy (FT-IR), Elemental Analyses, Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES), were used to study the chemical features of the precipitated lignin-manganese composites, as well as the amount of metal ions presented in the solution or adsorbed on precipitated lignin. The results showed that the hydrogen peroxide decomposition in the presence of both free manganese and precipitated lignin-combined manganese can be represented by a pseudo-first-order kinetics. The decomposition of hydrogen peroxide by free manganese ion under alkaline condition was significantly greater than when precipitated lignin was present, with pseudo-first-order rate constants of 2.89*10(-2) min(-1) and 6.53 *10(-4) min(-1) respectively. EDTA added individually showed the most positive effect on further reducing the decomposition of peroxide in both cases, dropping the pseudo-first-order rate constant (k(obs)) to 2.57*10(-4) min(-1) in the case of free manganese, and to 3.44 *10(-4) min(-1) in the presence of lignin-combined manganese. Analysis showed that only a small amount of Mn in solution is complexed by the lignin so a significant amount of free Mn is still present after complexation. Hence it is not clear whether the complexed Mn is the critical factor in this lignin effect or whether the lignin itself is acting as a peroxide stabilizer.