Abstract: The invention relates to a process for bleaching preoxidized paper pulp enabling a pulp having a very high degree of whiteness to be obtained with a limited number of treatment steps and enabling pollution to be reduced without degrading the qualities of the pulp; such a process essentially comprises the combination of the three successive treatment steps, namely:(a) a first step of hot chlorination with gaseous chlorine at a temperature of between about 30.degree. and 80.degree. C., and preferably between 35.degree. and 50.degree. C., in the presence of urea used at a rate of 0.5 to 5% by weight of the chlorine used, and preferably from 1 to 3%, with a concentration of pulp of between 3 and 30%, and a duration of retention of the chlorine of 30 seconds to 45 minutes;(b) a second step of alkaline extraction in the presence of an oxidizing agent of the hypochlorite or peroxide type, at a temperature of between about 30.degree. and 70.degree. C., and at a pH of between about 8 and 12, and preferably between 10.

Abstract: The delignification and bleaching of lignocellulosic products is effected by mixing an aqueous suspension of the lignocellulosic product with a chlorine-containing substance and an oxygen-containing substance, simultaneously or sequentially, and they, by reaction in situ, give rise to gases in the nascent state. The chlorine and/or oxygen are in the so-called "singlet" state, or in a state of higher energy. The treatment occurs at a temperature below 100.degree. C and for a time less than 60 minutes.