Abstract: A process for the chlorine-free bleaching of pulps in an aqueous suspension which comprises forming the suspension with a consistency of 3 to 20 mass percent; introducing into the suspension an ozone-containing gas having an ozone content of 20 to 300 g/m.sup.3 in an amount corresponding to at most 2 mass percent ozone calculated on dry pulp of the suspension during vigorous agitation of the suspension to form a reaction mixture; maintaining a pressure of the ozone-containing gas at a pressure of 1 to 15 bar during introduction into the suspension; and controlling reaction conditions during contact of the ozone-containing gas with the suspension to maintain a reaction temperature of 15.degree. to 80.degree. and a pH value of 1 to 8.

Abstract: A three-stage bleaching process for dissolving grade pulp utilizes the sequence OP(alkaline)-Z-P and the off gas from the Z-stage is delivered to the alkaline (OP)-stage whose parameters are controlled to fully react all of the oxygen of the off gas. The filtrate or waste water from the Z-stage, at a pH below 3, serves to dilute the alkaline OP-stage pulp before Z-stage bleaching and/or for de-ashing of the P pulp following the P-stage.