Refiner bleaching with magnesium hydroxide (Mg(OH)2) and hydrogen peroxide

Conventional bleaching of mechanical pulp with magnesium hydroxide and hydrogen peroxide shows significant economic benefits over bleaching with caustic soda and sodium silicate. Magnesium hydroxide [Mg(OH)2] bleaching generates lower effluent BOD/COD, higher pulp yield, lower anionic trash in the paper machines, reduced oxalate scaling and, in some cases, higher bulk. NORPAC has developed this bleaching process into a commercial, patented refiner bleaching technology. The excellent mixing, high temperature, and high consistency of the refining environment solubilize the magnesium hydroxide and provide an excellent bleach reactor with the addition of hydrogen peroxide. We have shown that by adding magnesium hydroxide into the refining system, refiner energy demand is reduced by 100-200 KW-hr/odmt and pulp strength is improved by 5-10%. In this paper, we describe NORPAC’s development of refiner bleaching, University of Maine lab refiner studies that support NORPAC’s work, and the additional benefits this technology provides to the mill.