| The mechanism of Mn2+-induced alkaline peroxide decomposition was studied. It was found that during the decomposition, a steady state of Mn3+ concentration was attained until the hydrogen peroxide concentration became zero. At zero hydrogen peroxide concentration, the Mn 3+ concentration increased to a maximum, then decreased due to hydrolysis to form MnO2. Removal of O2 from the system by N 2-purge slowed down the rate of decomposition, and the rate of decomposition was the same whether manganese was added as Mn2+ or Mn 3+. Based on these observations a mechanism for Mn2+-induced peroxide decomposition was proposed.; Manganese dioxide is one of the stable oxidation states of manganese. The catalytic activity of MnO2 and Mn2+ were compared and it was found that Mn2+ was more reactive than MnO 2 in decomposing hydrogen peroxide. The rate of peroxide decomposition was higher with MnO2 in powder form than in particulate form. The addition of stabilizers such as EDTA, DTPA and MgSO4 and Na 2SiO3 slowed down the redox cycle due to the formation of stable complexes. A mechanism for MnO2-induced peroxide decomposition was proposed.; It was demonstrated that the Mn-induced peroxide decomposition can be stopped when sodium silicate is used in combination with precipitated calcium carbonate. The potential to decrease peroxide decomposition was also investigated by adding zeolites to the silicate based peroxide system. The results show that the combined effect of zeolites and sodium silicate was more effective than sodium silicate alone in decreasing the Mn-induced peroxide decomposition. Two types of zeolites, X and Y were studied.; The Mn2+-induced peroxide decomposition in a magnesium hydroxide system using commercial magnesia slurry was studied. The results showed that the peroxide decomposition occurs under the bleaching conditions, as a result of impurities especially, manganese. Similar to the conventional sodium hydroxide based process, sodium silicate or DTPA can effectively decrease the Mn-induced peroxide decomposition in the Mg(OH)2 based system. |
