APPLICATION OF Mg(OH)2 IN D1/CEpD2 BLEACHING OF POPLAR KRAFT PULP

摘要

The substitution of Mg(OH)2 for NaOH used in Ep stage as alkali source and in D2 stage as pH controller of D1/CEpD2 bleaching of poplar Kraft pulp was carried out in this paper. The results showed that the substitution of Mg(OH)2 for NaOH as alkali source for Ep stage yielded the pulp lower brightness, higher Kappa number and higher pulp yield with a lower chemical oxygen demand (COD) in effluent. Through the following chlorine dioxide (D) bleaching, the Mg(OH)2 substituted Ep pulp gave 82.0 %ISO final brightness, similar to that of NaOH-based Ep pulp, 82.4 %ISO. The final strength properties of these two pulps have no big differences. For D1/CEpD2 bleaching, the use of Mg(OH)2 in Ep stage has no effect on the final pulp properties except lower COD and higher pulp yield. When the Mg(OH)2 was used in final D stage as pH controller instead of NaOH, the resulting bleached pulp also gives similar brightness and tensile. It is concluded that substitution of caustic soda with magnesium hydroxide is feasible in the Ep and D stages, while maintaining final pulp brightness and lowering chemical oxygen demand (COD).