Development of Light Absorption in Different Bleaching Stages Applied to Oxygen Delignified Softwood Kraft Pulp, 1996 International Pulp Bleaching Conference Proceedings

Maria Boman & Göran Annergren

SCA

A method for determining light absorption of dissolved substance in terms which match the determination of light absorption in pulp has been tested on spent liquors from different bleaching stages applied to oxygen delignified softwood pulps. Light absorption of pulp before and after chlorination at two different chlorine charges and alkaline extraction, chlorine dioxide treatment and a reinforced alkaline extraction, ozone treatment as well as peroxide treatments was compared with that which was determined for the corresponding spent liquor. Significant differences between the studied chemicals were obtained. The net result of the treatments was that chlorination increased the total light absorption (of treated pulp and spent liquor) while chlorine dioxide, ozone and hydrogen peroxide decreased it. Substantial brightening of the residual lignin in pulp was indicated only for the different peroxide stages.