Use of zeolites in hydrogen peroxide bleaching of pulp

The use of zeolites for inhibition of transition metal catalyzed decomposit ion of hydrogen peroxide was evaluated. A number of zeolite types (A, P, Y, and mordenite 10A), with different crystal structures and ion-exchange cha racteristics, were tested as additives in bleaching experiments using a mec hanical (TMP) pulp and a chemical (kraft) pulp. For the mechanical pulp, ad dition of zeolites A and P at a moderate alkali charge resulted in a signif icant improvement of the bleaching performance as signified by an increase in both brightness and residual peroxide content of the bleaching liquor. T he other zeolite types studied did not give any positive effects at the ble aching conditions used. For the chemical pulp, no significant improvements were obtained at any alkali charge using zeolite A as an additive. At high alkali charges, addition of zeolite A resulted in a substantially lower bri ghtness than that reached in a zeolite free reference experiment. The effects of zeolite addition upon the bleaching of pulp are complex and dependent upon a number of factors. Parameters of great importance are the bleaching pH, consistency and the zeolite type and charge.