Optimisation of froth flotation for removal of wood extractives in paper manufacture

A laboratory scale froth flotation batch process has been optimised for removal of wood extractives from Pinus radiata thermo-mechanical pulp (TMP) process water. This has provided insight into the mechanism of flotation and has potential for application in industry. The study involved optimisation of surfactant type and concentration, flotation time, airflow, impeller speed, pH, temperature and ionic strength.

Maximum wood extractive removal was achieved by flotation with the addition of 80 mg/L of the cationic surfactant dodecyltrimethylammonium bromide (DoTAB) at pH 5.0 and 60 ºC for 20 min with an air flow of 4.5 L/min and impeller speed of 1300 rpm. Under these conditions the removal efficiency of total extractives was close to 95%. Process water treated in this way would be suitable for recirculation in a pulp or paper mill and would result in significant reduction in problems caused by accumulation of wood extractives.