Bleaching of Kraft Pulp by Means of Hydrogen Peroxide. The Effect of Acid Treatment and Calcium Chloride Treatment before the Last Stage

From the results of the experimental work conducted, it appears that hydrochloric acid pretreatment of chlorinated and caustic extracted, and, also, chlorinated, caustic extracted, and calcium hypochlorite bleached kraft pulp before last stage hydrogen peroxide bleaching was not beneficial to final brightness. Calcium chloride pretreatment, on the other hand, was definitely of value to final brightness in three stage bleaching. However, calcium chloride pretreatment of chlorinated, caustic extracted, and calcium hypochlorite bleached kraft pulp did not increase pulp brightness to a significant extent. It seems, therefore, that there was an optimum concentration of calcium salts which was of maximum benefit to brightness. Also, there was some indication that both hydrochloric acid and calcium chloride pretreatment of the calcium hypochlorite treated pulp caused small increases of reflectance in the yellow-orange range of the spectrum