Peroxide bleaching refiner pulp - at high initial pH, lower end pH and with limited addn. of silicate

摘要

Cellulose pulp si prepd. by refining chips, partic. a thermo-mechanical pulp prepd. from steam-preheated chips with addn. of silicate e.g. Na silicate. Bleaching takes place esp. after a pre-treatment with a complexing agent, e.g. ethylene diamine tetraacetic acid, or with CaCl2. In the initial bleaching phase, alkalinity of bleaching liq. is such that the liq. has a Ph of 11-12 (11.5-12) measured in pulp suspension. Quantity of silicate added to reduce buffer capacity of system is 50, esp. 30 kg/t of absolutely dry pulp, so that pH 9-10.5 (9.5-10) measured in pulp suspension is achieved during end-phase of bleaching. Brightness values of 80% SCAN are achieved.