Acid Hydrogen Peroxide Treatment of Norway Spruce TMP: The Effect of an Extended pH Range when Catalyzed by Free Ferrous and Free or EDG/EDTA-Chelated Ferric Ions

Abstract

The influence of different types of iron salts (i.e., ferrous or ferric cations with sulphate, nitrate or chloride anions) on the reaction between coarse thermomechanical pulp and acid hydrogen peroxide (Fenton chemistry) was studied when the initial pH was 3.2 and 5.3. Also, ferric ions chelated with EDTA or EDG at different molar ratios were compared with ferrous sulphate when the initial pH was extended from about 3 to 8. Different anions of ferric ion salt gave a similar catalytic effect. At an initial pH of 7–8, the ferric-EDTA catalyzed reaction resulted in similar or higher hydrogen peroxide consumption and more detectable hydroxyl radicals than the ferrous sulphate catalyzed reaction, but less reaction with the pulp was indicated. Between pH 5–8, using Fe-EDG as a catalyst gave higher hydrogen peroxide consumption and more detectable hydroxyl radicals than if using ferrous sulphate; however, the measured effect on the pulp was similar or less.

Keywords:

• Hydrogen peroxide
• TMP
• Fenton’s reagent
• hydroxyl radicals
• ferrous
• ferric
• sulphate
• nitrate
• chloride
• EDTA
• EDG
• TOC
• total fiber charge

Acknowledgments

The authors gratefully acknowledge the financial support from the Swedish Knowledge Foundation. Jim LePage and Arjen Reichwein (AkzoNobel Functional Chemicals) are acknowledged for accessing the chelating agents and for valuable discussion. We also would like to thank Katarina Gutke and Pär Nilsson (AkzoNobel Pulp and Performance Chemicals) for help with laboratory work and modeling of hydrogen peroxide decomposition.