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High and uncontrolled surface active substances (SAS) concentrations in deinking line process waters strongly disturb flotation deinking. Indeed, their adsorption at air/water and ink/water interfaces stabilizes air bubbles and ink particles, reducing ink collection during flotation. In addition, foam stabilization promoted by SAS reduces froth drainage and consequently enhances suspended solids losses. All in all, selectivity of flotation is negatively affected by excessive SAS concentrations. Floating process water with adapted technology, a patented solution, is an efficient way to decrease SAS concentration and thereby recover flotation deinking selectivity. This concept was tested at industrial scale with success. First loop clear filtrates of a deinked pulp line (for newsprint production) were floated. At steady state, this treatment allows a 20% reduction of the SAS concentration in first loop process water. Evaluation of ink removal selectivity at pre-flotation and post-flotation showed a significant improvement in comparison with reference values. During the trial, the mill could either produce pulp with lower ink content and consequently higher brightness (50 ppm effective residual ink concentration [ERIC] less, corresponding to a 1 brightness point increase) for similar losses, or similar pulp quality with 1% to 2% yield improvement, representing a huge cost reduction. In addition, beneficial side effects were reported, such as reduced deinking chemicals consumption (soda, silicate, and bleaching agents) and better paper machine runnability, especially in terms of stickies breaks.

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