Magnesium Hydroxide Slurry as a Caustic Soda Replacement and Cellulose Protector in Pulp Bleaching

Magnesium Hydroxide Slurry as a Caustic Soda Replacement and Cellulose Protector in Pulp Bleaching

CellGuard^® OP magnesium hydroxide slurry can offer several economic and process benefits in mechanical and chemical pulp bleaching. Cost savings from the reduction or elimination of certain bleach chemicals can be achieved by employing CellGuard^® OP as an alternative alkali and cellulose protector. Additional benefits such as a reduction in BOD/COD and anionic trash can improve wastewater treatment and papermaking operations downstream.

In mechanical pulp bleaching, CellGuard^® OP has successfully replaced caustic soda and sodium silicate to yield significant cost savings for the mill. Since Mg(OH)2 is considered a weak alkali compared to caustic, there is less BOD and COD generated in the bleach effluent which translates to a higher pulp yield. Also, by eliminating or reducing caustic soda and sodium silicate, scaling due to silicate and oxalate salts is reduced and there is less anionic trash sent to the paper machines which can result in lower retention aid usage.

Kraft mills (i.e. chemical pulp mills) have also benefited from using CellGuard^® OP in their bleach process. For Eop or Ep bleaching, there is significant cost savings to be gained by partially replacing caustic soda in the extraction stage as well as completely replacing magnesium sulfate as a cellulose protector. Since CellGuard^® OP contains both magnesium ions and hydroxyl ions, it has a dual function as a cellulose protector and alkali. Kraft mills currently using CellGuard^®OP have also demonstrated a reduction in peroxide and chlorine dioxide for additional cost savings. Replacement of magnesium sulfate with CellGuard^® OP in the oxygen delignification stage has also been explored as a potential application for magnesium hydroxide.

CellGuard^® MH, a high purity magnesium hydroxide powder, can also be used as a cellulose protector instead of magnesium sulfate in oxygen delignification, as a substitute for caustic soda and sodium silicate in mechanical pulp peroxide bleaching, and as a partial replacement for caustic soda in EOP/EP and chlorine dioxide bleaching of chemical pulp.