High and uncontrolled surface active substances (SAS) concentrations in deinking lines process waters strongly disturb flotation deinking. Indeed, their adsorption at both air/water and ink/water interfaces stabilizes both 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 concentration. Floating process water with adapted technology is an efficient way to decrease SAS concentration and therefore 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. Ink removal selectivity achieved at both pre-and post-flotations was evaluated showing a significant improvement in comparison to the reference situation. During the trial, the mill could either produce pulp with lower ink content and consequently higher brightness (50 ppm ERIC less, corresponding to 1 brightness point increase) for similar losses, or similar pulp quality with 1 to 2% yield improvement representing huge cost reduction. In addition, beneficial side effects were reported such as reduced deinking chemicals consumption (soda, silicate, bleaching agents...) and better paper machine runnability especially in terms of stickies breaks.
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