PEROXIDE, OXYGEN, AND PEROXIDE/OXYGEN BRIGHTENING OF CHEMICAL AND MIXED WASTE PULPS

摘要

A composition and method for use in the peroxide, oxygen, or peroxide/oxygenstage of brightening pulps with less than 18 % ligninutilize a megnesium compound in a sodium silicate solution to form a higherpercentage of high molecular weight silicates. Such highmolecular weight silicates preferentially adsorb transition metal impuritieswhich, if left in solution, would tend to decompose hydrogenperoxide and organic peroxides. Hydrogen peroxide is added to peroxide andperoxide/oxygen stages, while it is generated, along withorganic peroxides, during an oxygen stage. Decomposition decreases the amountof peroxide that actually reacts with lignin and generatesfree radicals that attack the desired product, carbohydrate fibers. The highmolecular weight silicates can be formed by using any magnesiumcompound which dissociates to form Mg(OH)+ cations, which in turn cause asilicate polymerization reaction. The formation of Mg(OH)+cations from magnesium compounds occurs most realidy over a pH range of atleast about 8 and preferably between about 8 and about 12.The magnesium compound is added in an amount to achieve an Mg:SiO2 mass ratioof between about 1:46 to about 1:2, and preferablybetween about 1:15 to about 1:3.