Comparison of foaming agents for selective froth flotation of wood extractives from Pinus radiata TMP process water

A range of surfactants have been compared for use as foaming agents in froth flotation for removal of wood extractives from thermo mechanical pulp (TMP) process water. The surfactants studied were dodecyltrimethylammonium bromide (DoTAB), hexadecyltrimethylammonium bromide (CTAB), sodium dodecyl sulphate (SDS) and (1,1,3,3-tetramethlbutyl)phenyl-polyethylene glycol (Triton X-100). The surfactants were evaluated on the basis of their selectivity for removal of wood extractives. The cationic surfactants DoTAB and CTAB were found to be the most effective for removal of extractives, concentrating the solution by a factor of 6 at pH 6.5. Triton X-100 concentrated the extractives by a factor of 3.5, while addition of SDS did not provide any improvement over the inherent surfactant properties of the process water. The selectivity of extractives removal with these cationic surfactants was found to be dependent on pH with higher selectivity achieved at pH 6.5 over pH 5.0. This can be explained by ionic interactions with resin and fatty acid anions in the colloidal phase. In all cases, the resin acids were concentrated to a higher degree than the fatty acids or triglycerides. This effect was most pronounced in flotation with DoTAC, CTAB and Triton X-100, in which the concentration factor for resin acids was more than twice that for fatty acids or triglycerides. It is unclear whether this is due to selective flotation of fibre particles which are high in resin acids or due to removal of resin acids from the fibre or colloid surfaces. Further work is required to determine this. It is also expected that further optimisation of parameters including temperature, pH, surfactant concentration and airflow will result in more selective flotation of extractives.