Patent ID: 6010594
Filing Date: 2000-01-04
Classification: D21C

Abstract:
A method of processing cellulose pulp having a consistency between 5-18% containing undesirable heavy metals without the use of chlorine bleaching chemicals, comprising the steps of:(a) cooking and delignifying comminuted cellulosic fibrous material to produce cellulose pulp having a consistency between 5-18% and a kappa no. of about 14 or less and containing undesirable heavy metals;(b) bleaching the pulp having a consistency between 5-18% from step (a) using a (ZT) stage having a Z-portion and a T-portion, said (ZT) stage practiced by (i) if the pH of the pulp is not within the range of 2-7, adjusting the pH so that it is within the range of 2-7; (ii) bleaching the pulp with ozone in the Z-portion, and then removing gas from the pulp, and then adding alkali and complexing agent; and (iii) in the T-portion substantially immediately after the degassing, alkali addition, and complexing agent addition following ozone bleaching in substep (ii), without intervening washing, removing undesirable heavy metals from the pulp by using the complexing agent in the T-portion;(c) after step (b) washing or thickening the pulp; and(d) after step (c), bleaching the pulp in at least one additional stage with peroxide alone, or peroxide in combination with ozone or oxygen, to produce a bleached pulp.