Purification of white waters by selective flotation

Abstract

Removal of detrimental contaminants from paper machine circulation waters is known to benefit process runnability and paper quality. The applicability of selective flotation to remove substances of a hydrophobic nature from paper machine circulation waters was investigated in laboratory-scale experiments. The separation efficiency of ink, stickies, and wood extractives was studied by using a flotation scheme in which the froth was generated by the white water’s inherent surface active components without any chemical addition. The removal efficiency of detrimental contaminants was considered in relation to total losses of solid materials. The results showed that while not all white waters were able to produce stabile froth, those that generated froth also exhibited substantial separation of contaminants in the froth. With a moderate removal of 10% of total solids from white waters, removal of 45% of stickies, 27% of ink, and 20 to 50% of wood extractives was observed. Higher removal of contaminants resulted in solids losses at levels that are not economically feasible in paper production. The results showed that selective white water flotation can have beneficial results for papermaking processes.