Method for delignifying or bleaching cellulose pulp wherein chlorine is added to recycle liquor to regenerate chlorine dioxide

A method for delignifying or bleaching cellulose pulp which comprises in at least one stage adding a liquid containing chlorine dioxide to the cellulose pulp;

• reacting the cellulose pulp with the chlorine dioxide over a selected period of time;
• and then decreasing the amount of active chlorine available to the pulp by removing at least a substantial amount of the chlorine by removing a portion of the liquid accompanying the pulp;
• replenishing active chlorine as chlorine dioxide in the liquid removed from the pulp by regenerating chlorine dioxide in situ by adding chlorine as chlorine only in an amount from 10 to 35% of the amount of active chlorine already present in the liquid;
• and then recyling the replenished liquid as chlorine dioxide liquor to newly supplied cellulose pulp for delignifying or bleaching the pulp.