Improving chlorine dioxide bleaching efficiency by selecting the optimum pH targets

When operating chlorine dioxide (D) bleaching stages under mill conditions, it is important to establish reasonable operating targets and ranges. We examined the relationship between optimum pH, acceptable range for pH control, bleaching efficiency, and mill specific parameters such as wood species, pulp quality, and chemical charge. The D stages of eight separate fiber lines were simulated in the laboratory using mill pulps obtained from the various bleach plants studied. Both hardwood and softwood species were examined. We examined each simulated D stage over a range of final pH targets and chlorine dioxide charges to determine the relationship of pH to bleaching efficiency. Our work shows that, in practice, the optimum pH for a specific D stage varies with mill specific parameters. We categorized these practical relationships to draw some general conclusions. Mill data from three mill trials were used to validate the relationships.