Study On The DCS Generation In The Bleaching Of Wraste Newsprint Paper By Catalysed H₂O₂

In recent years, the recycling of waste paper becomes more and more important. But in the process of recycling, especially in the pulp bleaching process within alkaline environment, it would produce some dissolved and colloidal substances (DCS).Usually, those substances carry negative charge which will distract the effect of cationic additives used and break the balance of wet-end chemisty, consequently leading to the poor runability and paper quality.. So the feasibilty of using catylized H2O2to bleach waste newsprint pulp has been done in this research, in order to reduce or avoid the generation of DCS in the bleaching process.In this work, the deinking pulp from Huatai company and self-made were selected as study object. The forming rules of DCS within the bleaching of deinking pulp which were bleached by hydrogen peroxide in alkaline/catalytic acidic environment were studied, and especially discussed and contrasted the related factors of bleaching effect and the release of DCS. The second bleaching stage by hydrogen peroxide in alkaline environment and FAS were also discussed particularly.The experimental results show that dissolved and colloidal substances generated from bleaching of deinking pulp contain many inorganic substances, because ash content accounts for more than65%of the DCS. Watersoluble DCS account for more than80%of the DCS, which carbohydrates account for the vast majority and inorganic account for a small proportion.There are more dissolved and colloidal substances generated from bleaching of deinking pulp by hydrogen peroxide in alkaline environment than in acidic environment. The related factors of the release of DCS in alkaline environment are the dosage of hydrogen peroxide and sodium hydroxide. The related factors of the release of DCS in catalytic acidic environment are pH and the dosage of hydrogen peroxide and molybdate.The weight of dissolved and colloidal substances generated from bleaching of deinking pulp from Huatai company by hydrogen peroxide in alkaline environment are similar with that in acidic environment, but it is different in self-made deinking pulp. The weight of dissolved and colloidal substances generated from bleaching of deinking pulp from Huatai company by hydrogen peroxide in acidic and catalytic acidic environment are equally, and their whiteness of pulp are similar. But it is different in self-made deinking pulp, which indicated that the possible contaminants existing in the pulp has a great effect on the bleaching of catalysed H2O2.The activation effect of TAED is obviously in deinking pulp’s bleaching by hydrogen peroxide in alkaline environment. It can improve the pulp’s whiteness about3.5%ISO in a low temperature and short time, and the weight of dissolved and colloidal substances is similar with the traditional bleaching. The activation effect of TAED in catalysed H2O2is unprofitable compared with bleaching in alkaline environment.The weight of dissolved and colloidal substances generated from bleaching of deinking pulp by the second bleaching stage of FAS is about0.015g/5ml, which are half less than the first bleaching stage. And the release of dissolved and colloidal substances in the first bleaching stage of catalytic acidic is marginally, it would solve the problem of DCS in papermaking. So we can find that bleaching in acidic environment for the first stage and FAS for the second stage is the best combination, which could be a new way to optimize the bleaching process.