Used paper recycling

摘要

To process used paper, for recycling, a selective flotation is used for ink removal followed by at least one further cleaning flotation stage, using a multistage flotation for the selective flotation. The collected flotation foam is gathered together at the laest after the third flotation and cleaned in a total flotation through pressure relaxation. The foam, carrying impurities, is sepd. from the clear water and removed after further thicknening if required. The foam or sludge from the final first to third flotation stages or the second stage in a double flotation, is sepd. from the coarse dirt and fibres in one or two washing stages, and the fibres are further sepd. from the dirt. The fraction with a low fibre content is given a pressure redn. flotation to separate out the fine dirt. The fraction with a fibre content, and the clear water from the total flotation, are returned to a point in front of the flotation assembly. With a double-stage sieve action, the coarse particles in the first fraction are mostly retained. The material with a fibre content is sepd. as a third fraction at the second stage and returned to a point in front of the selective flotation. The material contd. in the fourth fraction, together with the first fraction, is passed to the total flotation.