Increasing the selectivity of ozone bleaching of eucalypt kraft pulp. Part B

Ozone appears to be an effective bleaching agent for the TCF process. However, bleaching sequences involving a Z stage require optimisation to overcome low selectivity. In this work, various reagents were used in treatments preceding the ozone bleaching stage in order to increase its selectivity. Eight reagents were used under different conditions to test 26 different pretreatments. Two additional treatments consisting of a combination of a pretreatment and an additive (Pret+Addit) were also studied. Overall, the pretreatments had favourable effects (particularly those involving chelating agents or acids). Pret+Addit treatments were found to be even more efficient, probably due to the additive effect in the Z stage.