Two-Stage Peroxide Bleaching of Eucalypt-SGW with Chromium Catalysts

Abstract

The addition of chromium nitrate to a two-stage hydrogen peroxide bleach of Eucalypt SGW can enhance the brightness of the pulp. It is proposed that radicals produced in the catalytic decomposition of hydrogen peroxide by chromium under acidic conditions participate in reactions which render the chromophores more susceptible to bleaching in the alkaline stage. This two-stage process, under optimised conditions, consumes no more peroxide than a traditional single stage alkaline bleach and allows the pulp to be bleached to a given brightness in a shorter time. Enhanced bleaching response was also observed for a two-stage acid/alkali peroxide bleaching sequence without the addition of chromium, and we have attributed this effect to catalytic effects of transition metal ions which occur naturally in the pulp.