BICARBONATE ANION AND TAED AS ACTIVATORS IN PEROXIDE BLEACHING OF A MECHANICAL PULP

Earlier research demonstrated that the bicarbonate anion (HCO 3 -) activated hydrogen peroxide and made it into an effective bleaching agent for both chemical and mechanical pulps at pH ~ 8.5. The peroxide/bicarbonate treatment is designated as a P B stage. It was also observed that in P B bleaching of chemithermomechanical pulps (CTMPs), a higher initial pH resulted in more H 2 O 2 being consumed and the achievement of a higher bleached brightness. This research focused on using Na 2 CO 3 instead of NaHCO 3 to achieve a higher pH in P B bleaching of softwood CTMP. Further activation of the H 2 O 2 was obtained by the addition of N, N, N', N'-tetraacetylethylenediamine (TAED). There was a high peroxide residual when 3.0% H 2 O 2 on pulp (oven-dried or OD basis) was used in a conventional alkaline peroxide (P) stage. Sodium carbonate was added to the P stage effluent (with or without TAED), which was recycled and used to pretreat unbleached pulp. A significant increase in brightness (~3 points) was obtained when the pretreated pulp was regularly bleached with 3.0% H 2 O 2 on pulp in a P stage.