| 摘要 |
Up to now, full scale use of the from the environmental point of view excellent bleaching agent ozone, has been hampered e.g. by the comparatively large amounts required and the excessive depolymerization of the pulp. The present invention aims at solving these problems and relates to a three-step method for bleaching chemical pulp with a lignin content corresponding to a kappa number not exceeding 10. This method is characterized in that the bleaching begins with a chlorine dioxide step at a comparatively high pulp consistency, and that the pulp, after the bulk of chlorine dioxide has been consumed, is intimately contacted with an ozone-containing aqueous solution and brought to react with the ozone at a considerably lower pulp consistency than in the chlorine dioxide bleaching, whereupon the pulp undergoes an alkaline treatment in the presence of oxygen and/or an oxidizing agent giving off oxygen. |
