Chlorine dioxide bleaching of chemical pulp

摘要

PCT No. PCT/SE91/00178 Sec. 371 Date Oct. 2, 1992 Sec. 102(e) Date Oct. 2, 1992 PCT Filed Mar. 7, 1991 PCT Pub. No. WO91/17306 PCT Pub. Date Nov. 14, 1991A method of bleaching chemical pulp in a sequence comprising at least four bleaching steps with final bleaching in a first and a second chlorine dioxide step. Between the chlorine dioxide steps an alkaline extraction is carried out, and washing takes place between the first chlorine dioxide step and extraction. Immediately after said washing step, NaOH is charged in an amount of 4-10 kg/ton pulp. Thereafter an oxidizing agent is admixed in an amount of at maximum 2 kg/ton pulp. After 15-120 seconds an acid is added for terminating the oxidation treatment and for lowering the pH-value, but without effecting a complete neutralization of residual alkaline.