Patent ID: 6331192
Filing Date: 2001-12-18
Classification: D21C

Abstract:
A process for bleaching chemical pulp, wherein the pulp is subjected to a first treatment step including at least one of a delignification treatment and a bleaching treatment, said first treatment step comprising admixing said pulp with a treatment chemical selected from chlorine dioxide and an admixture of chlorine dioxide and a per-compound, and said process further including a second treatment step wherein the pulp is chelated by contact with a chelating chemical to bind heavy metals into a chelate complex, the process comprising:subjecting said pulp to said first and said second treatment steps substantially simultaneously by combining, in a single stage, said pulp with said treatment chemical and said chelating chemical; andchoosing said chelating chemical from a material selected from the group consisting of N-bis-[(1,2-dicarboxylethoxy)-ethyl]-amine; N-bis-[(1,2-dicarboxylethoxy)-ethyl]-aspartic acid, N-tris-[1,2-dicarboxylethoxy)-ethyl]-amine and alkali metal and earth-alkali metal salts of these materials.