Removal of Lignin from Water by Precipitate Flotation

Flotation was effective for the removal of lignin from aqueous solution when alum (aluminum sulfate) was used as a precipitator and a cationic surface-active agent, such as a quarternary ammonium compound, was used as a collector. Lignin fractional removal of higher than 0.94 was obtained by using 40 mg/l of alum and 40 mg/l of quaternary ammonium compounds (as cetyldimethylbenzylammonium chloride) per 100 mg/l of lignin (as Indulin C). Initial pH values between 2 and 4 were found to be optimal. The superficial gas velocity should be controlled at some optimum value; for this research the value was 24.2 cm/min. Assuming a wastewater containing 100 mg/l of lignin (as Indulin C) is treated with 40 mg/l of alum and 63.3 mg/l of Arquad 2HT-75 (i.e., 40 mg/l as cetyldimethylbenzylammonium chloride) in a precipitate flotation system, the total treatment costs including chemicals would be $0.352/1,000 gal (or $0.093/1,000 l).