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/oxygen stage of brightening pulps with less than 18 % lignin utilize a megnesium compound in a sodium silicate solution to form a higher percentage of high molecular weight silicates. Such high molecular weight silicates preferentially adsorb transition metal impurities which, if left in solution, would tend to decompose hydrogen peroxide and organic peroxides. Hydrogen peroxide is added to peroxide and peroxide/oxygen stages, while it is generated, along with organic peroxides, during an oxygen stage. Decomposition decreases the amount of peroxide that actually reacts with lignin and generates free radicals that attack the desired product, carbohydrate fibers. The high molecular weight silicates can be formed by using any magnesium compound which dissociates to form Mg(OH)+ cations, which in turn cause a silicate polymerization reaction. The formation of Mg(OH)+ cations from magnesium compounds occurs most realidy over a pH range of at least about 8 and preferably between about 8 and about 12. The magnesium compound is added in an amount to achieve an Mg:SiO¿2? mass ratio of between about 1:46 to about 1:2, and preferably between about 1:15 to about 1:3.