Yield of Fillers and Fibers in Froth Flotation, 1994 Pulping Conference Proceedings

H. U. Süss, J. D. Kronis, N. F. Nimmerfroh, B. Hopf

Paper recycling with printing ink removal has become a very important part of paper production. The driving forces are to reuse valuable fibers and to unburden the landfills. Since the recycling process itself produces waste, which has to be dumped, yield in paper recycling is an important factor.

The froth flotation process produces higher yields compared with deinking by washing. Yield in froth flotation is affected by a number or parameters. One of these parameters is the chemistry of the repulping process. It has a lot of effect on the tendency of fillers and mechanical or chemical pulp fibers to float together with the froth.

The addition of sodium silicate and the amount of caustic soda with respect to the pH level during flotation affect the yield and the ash content of the deinked pulp. Additionally these chemicals have a significant influence on the selectivity of the printing ink removal and thus on the brightness development.

Recommendations are given how to optimize the froth flotation process.