Reduction of the Formation of AOX During Chlorine Dioxide Bleaching, 1996 International Pulp Bleaching Conference Proceedings

The substitution of chlorine dioxide (ClO2 ) for chlorine is expected to reduce the formation of AOX by 80 %. In some cases using ClO2 instead of Cl2 will be a satisfactory answer to meet the requirements on AOX rejects. However in other cases further reduction will be needed. A project has been developed to understand better the origin of AOX formation during ClO2 bleaching and to find the key process parameters which govern this formation. RESULTS AND DISCUSSION Schematic of ClO2 delignification The reaction taking place during ClO2 bleaching are quite complex and have been the subject of numerous investigations (l-3). It is well established that the reaction of C1O2 with lignin generates chlorite and hypochlorous acid The later. which is in equilibrium with chlorine. is responsible for the formation of AOX. Moreover hypochlorous acid and chlorine are involved in many other reactions taking place in solution which are summarized in figure 1. Some of these reactions have been well described in a series of papers (4-6).