Patent ID: 6123809
Filing Date: 2000-09-26
Classification: D21C

Abstract:
Process for the delignification and bleaching of chemical pulp comprising in this order:a) an acid treatment stage of the pulp in order to reduce the quantity of hexene uronic acids present in the pulp by at least 10%, the acid treatment stage of the pulp being conducted at a pH of 2 to 6.5 and at a temperature of between 85.degree. C. and 150.degree. C.,b) a pH adjustment stage of the pulp to a value of between 7 and 12 in order to deposit or redeposit ions of alkaline-earth metals on the pulp, by addition of an alkaline liquor and without addition of alkaline earth metal ions,c) a washing stage of the pulp,d) a treatment stage of the pulp with an oxidizing agent, together with at least one addition of a chelating agent to the pulp carried out before the acid treatment stage (a), during the acid treatment stage (a), before the pH adjustment stage (b), during the pH adjustment stage (b) or between the pH adjustment stage (b) and the washing stage (c), and wherein a washing stage between stages (a) and (b) is not carried out.