DELIGNIFICATION AND BLEACHING OF HARDWOOD KRAFT PULP WITH HYDROGEN-PEROXIDE AND NITROGEN-DIOXIDE

The influence of both H2O2 charge and of the time of hardwood kraft pu lp delignification on the technological and water-effluent indices of the process was investigated. It was confirmed that definite two-stage pulp delignification sequences with application in one of the stages of hydrogen peroxide or nitrogen dioxide generated in situ from acidif ied sodium nitrite, may decrease the kappa number to half of its initi al value, thus improving the brightness of pulp. The impact of convent ional multistage bleaching in GEHDED sequence, as well as in sequences with hydrogen peroxide or nitrogen dioxide, permitting to obtain pulp s of over 88% brightness, on the technological and water-effluent effe cts, were determined. The influence of replacing elemental chlorine by the mentioned chlorine-free delignification agents, on the decrease o f pollution load in effluents, including the AOX index and shortening of the time of bleaching process, was established.