APPLICATION OF MAGNESIUM HYDROXIDE IN EPD2 OF DiEpDz BLEACHING

摘要

The application of magnesium hydroxide in Ep stage as alkali source and in D2 stage as pH controlling agent, D1EpD2, was discussed in this paper. The efforts were focused on the differences between magnesium hydroxide-based and sodium hydroxide-based EpD2 bleaching process, and getting the optimal conditions of magnesium hydroxide-based EpD2 bleaching process. The results showed that, after Ep stage, both the NaOH-Ep stage and the Mg(OH)2-Ep stage can give the pulp 72% ISO brightness, or higher. Compared with NaOH-Ep treatment, the Mg(OH)2Ep treatment can lead the pulp to a little lower brightness and strength properties, but the CODcr of the bleaching liquid can reduce by more than 50%. When Mg(OH)2 is used in final D2 stage, as pH controlling agent, in D1EpD2 bleaching process, compared with NaOH-based D2 bleaching, the Mg(OH)2based D2 bleaching can give the resultant pulp higher strength properties and lower brightness.