Process for removing impurities from an aqueous fibrous material suspension

摘要

To remove impurities from a watery suspension of paper fibers, e.g. inks and stickies from used paper materials for recycling, the suspension is passed through preferably two flotation stages (1,2). The foam (3) from the first stage is added to the flow into the second stage. The outflow (4) from the second stage is divided into a first running fraction (5) and a return fraction (6). The volumes of the separated fractions are set according to the required quality of the cleaned suspension (9). The first running volume is reduced if the degree of whiteness is to be increased and the ash content lowered in the cleaned suspension. The foam taken from the first stage is reduced if the fiber loss is to be cut in the flotation assembly.