Klorfri blekning av kemisk pappersmassa

摘要

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; andbleaching the pulp with peroxide.