Abstract: Provided is a method of treating chemical paper pulp having the steps of: adjusting the pH of the pulp to be between 1 and 6; treating the pulp with ozone to reduce the kappa number of the pulp; treating the pulp with a chelating agent after the ozone treating step without any intervening washing step between the ozone treating step and the chelating agent treating step; adjusting the pH of the pulp by adding alkali together with or after the addition of chelating agent to a pH exceeding 3; washing the pulp; and bleaching the pulp with peroxide.

Abstract: A process for chlorine-free bleaching of chemical pulp in association with the production thereof, where a suspension of the pulp preferably has a concentration exceeding 8% of cellulose-containing fiber material and where the pulp entering into a bleaching line is preferably fed continuously through at least one bleaching vessel in the bleaching line, is treated with at least one acid for adjusting the pH to a value below 7, and with a chelating agent, and is subsequently bleached in at least one stage to a brightness exceeding 75% ISO, preferably exceeding 80%, with hydrogen peroxide or the corresponding quantity of another peroxide, employed in a quantity exceeding 5 kg/BDMT, where the peroxide bleaching takes place at elevated temperature and at a pressure in the bleaching vessel which exceeds 2 bar and where the cross-sectional area of the bleaching vessel exceeds 3 m.sup.2 and the area of the metal surface exposed towards the interior of the bleaching vessel is less than 4V m.sup.

Abstract: A method of manufacturing chemical pulp out of comminuted cellulosic fiber material comprising digesting the fiber material with digestion liquid without preceding peroxide stage. According to the invention the comminuted fiber material is treated in at least one stage prior to said digestion, in the presence of a liquid containing at least one compound having the ability to form complexes with metals existing naturally in the fiber material.

Abstract: A process for chlorine-free bleaching of chemical pulp in association with the production thereof, where a suspension of the pulp preferably has a concentration exceeding 8% of cellulose-containing fiber material and where the pulp entering into a bleaching line is preferably fed continuously through at least one bleaching vessel in the bleaching line, is treated with at least one acid for adjusting the pH to a value below 7, and with a chelating agent, and is subsequently bleached in at least one stage to a brightness exceeding 75% ISO, preferably exceeding 80%, with hydrogen peroxide or the corresponding quantity of another peroxide, employed in a quantity exceeding 5 kg/BDMT, where the peroxide bleaching takes place at elevated temperature and at a pressure in the bleaching vessel which exceeds 2 bar and where the cross-sectional area of the bleaching vessel exceeds 3 m.sup.2 and the area of the metal surface exposed towards the interior of the bleaching vessel is less than 4 V m.sup.