Pulp properties and effluent characteristics from the Mg(OH)2-based peroxide bleaching process

Softwood TMP was subjected to peroxide bleaching under various conditions, with either magnesium hydroxide (Mg(OH)(2)) or sodium hydroxide (NaOH) as the alkali source. The optical and physical strength properties of the bleached pulps were compared, as were the charge characteristics. The Mg(OH)(2) process was found to yield brightness and strength results similar to those of the conventional process, but the pulp from the Mg(OH)(2) process had a higher light-scattering coefficient. The bleached pulp from the Mg(OH)(2) process was lower in total carboxylic group content, but its surface charge density was close to that of pulp from the NaOH process. A lower COD load in the bleaching effluent from the Mg(OH)(2) process was found to be caused by the decreased formation of acetic acid and methanol and by the lower dissolution of lignin.