REDUCTION OF THE FORMATION OF ORGANICALLY BOUND CHLORINE DURING CLO2 BLEACHING

The formation of organically bound chlorine during the bleaching of ch emical pulp with chlorine dioxide can be reduced by equimolar replacem ent of part of the chlorine dioxide by chlorite. It is shown that a re placement of 30% of the chlorine dioxide by chlorite results in a 25% reduction in organically bound chlorine in effluent and C pulp while t he delignification is not affected. The addition of hydrogen peroxide also reduces the formation of organically bound chlorine during chlori ne dioxide bleaching. When an unbleached softwood kraft pulp of kappa number 28.7 was treated with chlorine dioxide at a kappa factor of 0.1 1, the addition of 0.1% H2O2 (based on pulp) reduced the organically b ound chlorine by 20%. Hydrogen peroxide can also be used to remove ele mental chlorine from industrial chlorine dioxide solutions, which lead s to a further decrease in the formation of organically bound chlorine during ClO2 bleaching.