Refiner Bleaching With Magnesium Hydroxide (Mg(OH)_2) And Hydrogen Peroxide

摘要

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 (Na_2O/SiO_2). 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.