VERFAHREN ZUR WEISSGRADERHOEHUNG VON ALTPAPIER MIT NEUTRALEM WASSERKREISLAUF

摘要

A de-inking and bleaching process for waste paper is described, which is operated without or with only minimal quantities of chemicals, especially alkali, in the pulper. After a first printing ink removal, for example by means of washing, a 2-stage bleach is carried out, preferably using the peroxide/ formamidinesulphinic acid (FAA) combination. After the 1st bleaching stage with peroxide, the pH is in the alkaline region at about 8.5 - 9.5. At approximately stoichiometric ratios of alkali and FAA, the pH in the medium is in the neutral region at 6.5 - 7.5 after the 2nd bleaching stage, without additional acidification being necessary. As a result, the purification of the circulating waters, for example by means of release flotation, is substantially facilitated. The 2-stage bleach is carried out, for example, as a combination of disperser bleach and bleach at medium stock consistency. After the disperser treatment, or after the bleach, a further removal of printing ink and dirt is carried out, for example by flotation or washing, nonionic frothing/collecting agents also having proved suitable. Residual peroxide from the 1st bleaching stage, which would destroy the FAA used in the 2nd bleaching stage, can not only be made harmless by addition of thiourea, but advantageously be converted to additional FAA.