Influence of Transition Metal Ions on High Consistency O3 Bleaching, 1996 Pulping Conference Proceedings

G.J. Kang

Y. Ni

A.R.P. van Heiningen

University of New Brunswick

In the present paper the influence of Fe 2+ , Fe 3+ , Cu 3+ and Mn 2+ on ozone treatment of a cellulose model compound solution, fully bleached pulp and unbleached Hemlock kraft pulp is studied. It was found that Mn 2+ had a slightly protective effect on pulp viscosity but no influence on the delignification and brightness during ozonation of unbleached pulp. However, Mn 2+ can lead to severe cellulose degradation in fully bleached pulp. These results indicate that although Mn 2+ can react with O2 to produce hydroxyl radicals, the presence of lignin suppresses this reaction. The explanation why Mn 2+ is protected by lignin from reacting with ozone is that under acidic conditions the oxidation of Mn 2+ to Mn 3+ is rather difficult due to the high oxidation potential of this reaction. The presence of ferrous during ozone bleaching may lead to additional carbohydrate degradation. At a concentration of below 100 ppm, the additional loss in pulp viscosity due to Fe 2+ is limited to about 2 mPa.s. At a much higher concentration of 500 ppm, ferrous may contribute to additional loss in pulp viscosity of about 4 mPa.s. The effect of ferric ion on the decrease in pulp viscosity during ozone bleaching of unbleached pulp is similar to that of ferrous. The presence of Cu 2+ has a minimum impact on viscosity for both fully bleached and unbleached pulp.