Sodium silicate is a key additive in mechanical pulp bleaching processes. Silicates stabilize bleaching liquors by complexing transition metals that catalyze hydrogen peroxide decomposition and by buffering the pH to eliminate alkali darkening. Optimizing silicate addition levels will increase pulp brightness and reduce bleaching costs.
Sodium silicate is also an important component in de-inking recycled paper. Silicates enhance ink removal and dispersion from paper fibers during pulping and flotation stages. They also act to stabilize hydrogen peroxide when it is added to improve brightness.
Magnesium sulfate protects pulp fibers from oxidative degradation during Kraft oxygen delignification stages. The addition of small quantities of magnesium allows removal of more lignin without loss of pulp strength. This process modification reduces chemical costs in later bleaching stages.