BLEACHING OF CHEMICAL PULP FOR UNBLEACHING PAPERMAKING AND BLEACHING AGENT AQUEOUS SOLUTION USED THEREIN

摘要

1. Process for bleaching chemical paper pulps using hydrogen peroxide, characterized in that the operation is carried out in a single stage at a pH of 11 to 11.5, at a temperature of 70 degrees C to 100 degrees C, with the aid of a solution containing, in addition to hydrogen peroxide, at least one alkaline agent chosen from sodium hydroxide and sodium carbonate, at least one alkali metal silicate at a concentration of at least 0.3% by weight, expressed as SiO2 , at least one magnesium salt and at least one calcium salt in such quantity that the weight concentration of each of these alkaline-earth elements is between 0.05% and 1%, these elements being maintained in the dissolved state with the aid of at least one complexing agent for alkaline-earth ions in such quantity that the total concentration of complexant does not exceed 10% by weight.