Abstract: A process for bleaching pulp, in which, after fiber liberation, a first filtrate containing metals, principally in ionic form, is separated off from the pulp, and supplied downstream to the pulp flow after a bleaching stage.

Abstract: The invention relates to a process for dividing up the sulphide content of green liquor into a sulphide-rich part and a sulphide-poor part by crystallizing out sodium carbonate (Na.sub.2 CO.sub.3). The crystallization of the sodium carbonate is effected by evaporating green liquor with a ratio of hydroxide ions [OH.sup.- ] and sulphide ions [HS.sup.- ] such that the liquor which is obtained after evaporation and separation of the solid phase has high sulphidity and an acceptably low content of carbonate ions [CO.sub.3.sup.2- ]. Prior to evaporation, the hydroxide ion content in the liquor is increased by adding quicklime (CaO). The solid phase (sodium carbonate and calcium carbonate) which has been separated off is diluted with water so that the sodium carbonate crystals go into solution and at the same time the solution is given a cation content which favours the causticization which is subsequently undertaken. The causticization is carried out in a conventional causticization plant.