Selective froth flotation of pitch components from spruce TMP process water

Selective removal of dissolved and colloidal pitch components from an unbleached thermomechanical pulp (TMP) pressate by addition of a cationic foaming agent, dodecyltrimethylammonium chloride (DoTAC), and subsequent froth flotation was assessed. The experiments were conducted with varying pH, temperature, and concentrations of DoTAC and calcium. The concentrations of pitch components, lignans, and dissolved polysaccharides were determined before and after flotation. All pitch components were removed more efficiently by flotation at pH 5 and 3.5 than by flotation at pH 7.6. Resin and fatty acids were removed to a higher degree than neutral pitch substances at all the tested pH levels. Most of the water-soluble uronic acids and galactoglucomannans stayed in the TMP water after flotation. Froth flotation with DoTAC was an effective way of selectively removing colloidal and dissolved pitch. Removal of pitch, especially of resin acids, at an early stage should be beneficial to the overall papermaking process.