Using Magnesium Hydroxide for pH Control to Improve the Chlorine Dioxide Brightening Stages in ECF Bleaching Sequences

摘要

We further determined the effect of using magnesium hydroxide (Mg(OH)_2) in controlling the pH during the chlorine dioxide brightening stages of an ECF bleaching sequence for both softwood and hardwood kraft pulps. The Mg(OH)_2-based process showed superior brightness gain for both the softwood and hardwood pulps in comparison to the control trials due to its flat pH profile. The improved results were explained by the decreased formation of chlorate. The alkali-induced decomposition of chlorine dioxide in a typical chlorine dioxide brightening stage results in the formation of more chlorate, which wastes some of the chlorine dioxide charged. The Mg(OH)_2-based chlorine dioxide minimize the formation of chlorate, thus improving the bleaching efficiency.