METHOD OF BLEACHING PAPER PULP Russian patent published in 2002 - IPC

FIELD: paper-and-pulp industry. SUBSTANCE: pulp is subjected to acid treatment to reduce, at least by 10%, level of hexeneuronic acids present in pulp. pH of the pulp is adjusted to precipitate or reprecipitate alkali-earth metal ions on pulp by adding alkaline solution without addition of alkali-earth metal ions. Pulp is washed and treated with oxidant. A chelating agent is added to pulp before acid treatment stage, in the course of acid treatment, before or during pH adjustment, and/or between pH adjustment stage and washing stage. Washing between acid treatment and pH adjustment stages is not effected. During chelation, pH changes and achieves value 9-12. EFFECT: increased economical efficiency due to reduced amount of reagents. 19 cl, 4 dwg, 5 tbl, 3 ex