Peroxide bleaching with zeolites. Part 2: Bleaching of pine TMP and eucalypt CCS

A combination of zeolite and sodium citrate was found to be an effective alternative to DTPA addition in alkaline peroxide bleaching of pine IMP in the presence of manganese ions, but not in the bleaching of Eucalypt CCS pulp. The addition of the zeolite had no effect on strength properties of the TMP and CCS pulps. Some small improvements in optical properties were observed. The type of zeolite used was important. Addition of small amounts of sodium citrate to the zeolite system improved the zeolite's ability to chelate metal ions from the pine TMP fibre. Sodium citrate appears to act as a transfer agent, facilitating the migration of metal ions from the pulp fibres to the zeolite. In the presence of manganese, the alkaline conditions of the Eucalypt CCS resulted in the formation of oxidized manganese species that actively decompose peroxide. Zeolite and citrate appear to be unable to complex these metal species. DTPA, on the other hand, is effective in complexing the Mn-O species present in CCS.