Pretreatment of Softwood Kraft Pulp in TCF Bleaching Using Ion Exchange with Magnesium and Calcium, 1996 International Pulp Bleaching Conference Proceedings

Harald Brelid, Tommy Friberg, Rune Simonson and Eva-Lena Strömberg

Chalmers University of Technology

TCF bleaching sequences including oxygen, hydrogen peroxide and peracetic acid as bleaching agents have been studied. The metal ion content of softwood kraft pulp was altered using an ion exchange procedure consisting of a pretreatment with magnesium and calcium acetate (Mg + Ca). Most of the manganese present in the pulp (95%) was displaced under slightly acidic conditions, and the effect of such a pretreatment on the metal ion content in the pulp was the same when the ion exchange was carried out before or after an oxygen delignification stage. The ion exchange pretreatment alone did not prevent a major viscosity loss during the bleaching, but if a two-step procedure consisting of an ion exchange step followed by EDTA-extraction was applied, the viscosity could be maintained at a high level at EDTA charges as low as 0.05-0. 1 kg/ton.