Modelling deinking selectivity in multistage flotation systems

Model equations and transport coefficients recently used to describe particle and water transport phenomena in a laboratory flotation deinking column were applied to industrial flotation cells and used to simulate multistage flotation systems. The deinking selectivity obtained for a two-stage pre-flotation system was in agreement with data collected in a deinking mill running in similar conditions and process yield, floated pulp composition and ink load in the floated pulp were predicted with good accuracy. Multistage flotation systems with different configurations were simulated, however, only a not conventional three-stage flotation system gave a relevant increase in the ink removal selectivity. Indeed, the addition of a third stage to a conventional two-stage flotation system gave ∼50% decrease in the pulp stock loss and only 10% decrease in ink removal which was recovered by the addition of a flotation cell in the first stage without affecting yield. In general, it was observed that the addition of second and third stages favours the selective removal of particles with the highest flotation rate constant (inks). Indeed, floatable particles, i.e. ink, fillers and fines are mainly removed in the first stage, ink and fillers in the second and ink in the third stage.