Near-Neutral Final Chlorine Dioxide Brightening: Theory and Practice, 2011 International Pulp Bleaching Conference

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It is well known that pH affects the effectiveness of chlorine dioxide treatment, but the standard recommendation has been to maintain a post-stage pH range for brightening with chlorine dioxide between 3.5 and 4. In this paper, we will confirm that the optimum pH for final chlorine dioxide bleaching is dependent on chlorine dioxide charge but that this stage should be operated with a final pH close to neutral when a typical chlorine dioxide charge is applied. We will also show that maintaining a pH close to neutral throughout the bleaching stage is the ideal strategy. This result can be achieved under unbuffered conditions in some instances but is more consistently obtained by generating sodium bicarbonate in situ by adding carbon dioxide to alkaline pulp or sodium carbonate to acid pulp. In addition, we will also highlight the theory and practice of the near-neutral final chlorine dioxide brightening technology.