Pilot Plant Studies of Office Paper Deinking. Part 2. Chemical Aspects of Process Design, 1998 Recycling Symposium Proceedings

Deinking tests were performed in a pilot plant using the following sequence of unit operations: pulping, screening, thickening, kneading, and flotation. Results suggested that, for a mixed office furnish containing substantial amounts of toner-printed paper, the optimum addition point of a proprietary surfactant was to the kneader. While the process conditions were not optimized for the surfactant used, overall ink removal efficiency was as great as 94%. The highest overall brightness gain was obtained in the experiment in which the same total amount of surfactant, 0.2%, was added in equal portions to the pulper and the kneader. Excessive amounts of surfactant addition resulted in less efficient ink removal. Surfactant dosage had little effect on ash removal or Canadian Standard Freeness values.

Toner ink particle folding was previously observed in laboratory disk dispersion tests by other workers and in our studies using a pilot scale twin-shaft kneader. Similar ink particle folding was observed in the present study using a twin-shaft kneader from another manufacturer.