Refiner Bleaching With Magnesium Hydroxide (Mg(OH)2) And Hydrogen Peroxide, 2006 Engineering, Pulping, & Environmental Conference

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Mill experience using a patented process with Mg(OH)₂ as the alkali source in refiner peroxide bleaching has shown significant benefits over conventional post refiner bleaching using caustic (NaOH) and sodium silicate (Na₂O/SiO₂). The peroxide stabilization and stable pH provided by the Mg(OH)₂ alkali source eliminates the need for sodium silicate. The excellent mixing, high temperatures and high consistency of the refining environment solubilize the Mg(OH)₂ and provide an excellent bleaching reactor with the addition of hydrogen peroxide. Mill data confirmed that using the divalent base Mg(OH)₂ has lowered BOD and COD in the effluent and improved TMP yield. Calcium oxalate scale deposits were eliminated when Mg(OH)₂ became the alkali bleaching source as magnesium complexes with oxalate keeping it in a soluble state. Additionally, reductions in refiner energy were realized due to adding the alkali (Mg(OH)₂) directly into the refiner.