Influence of magnesium addition on hydrogen peroxide bleaching of the acid treated pinewood kraft pulp

The effects of preliminary acid treatment and magnesium sulfate addition during hydrogen peroxide kraft pulp bleaching was evaluated. The magnesium retention level is similar after the acid treatment and after chelation. Independently of differences in native magnesium contents in pulp the addition of magnesium sulfate stabilizes hydrogen peroxide and limits its ability for delignification. Magnesium charge should be optimized for each type of pulp. Too low or too high level of magnesium causes the decrease of brightness and limits delignification. While the excess of magnesium does not influence negatively the degree of polymerization of cellulose.