Limits of Metal Removal from Kraft Pulp by Acid Treatment, 1996 International Pulp Bleaching Conference Proceedings

Luc Lapierre,Michael Paleologou, Richard Berry and Jean Bouchard

Pulp and Paper Research Institute of Canada

We have studied the metal removal capability of various acid treatments from kraft pulp and the response on the subsequent hydrogen peroxide bleaching stage. A significant improvement in metal removal was obtained for pulp treated with sulphuric acid for 5 hours at 95°C when compared to mild acid and chelation treatments. This improvement translated, after the subsequent peroxide bleaching stage, into significantly increas-ed brightness and lignin removal. The hypothesis that intract-able metals are inactive towards peroxide decomposition is incorrect. Unfortunately, this low level of metal in pulp, when achieved by a severe acid wash, was attained at the expense of pulp strength.We have studied the metal removal capability of various acid treatments from kraft pulp and the response on the subsequent hydrogen peroxide bleaching stage. A significant improvement in metal removal was obtained for pulp treated with sulphuric acid for 5 hours at 95°C when compared to mild acid and chelation treatments. This improvement translated, after the subsequent peroxide bleaching stage, into significantly increas-ed brightness and lignin removal. The hypothesis that intract-able metals are inactive towards peroxide decomposition is incorrect. Unfortunately, this low level of metal in pulp, when achieved by a severe acid wash, was attained at the expense of pulp strength.