Treatment of Polishing Wastewater from Semiconductor Manufacturer by Dispersed Air Flotation

Treatment of chemical mechanical polishing wastewater containing nanosized silica from semiconductor industry by dispersed air flotation was investigated. Very effective removal of particles from wastewater was found when cationic surfactant, cetyltrimethyl ammonium bromide (CTAB), was used as a collector. The flotation efficiency decreased slightly under a pH of 4.5. The zeta potential increased with a increasing concentration of CTAB, and flocculation of particles by CTAB was found. It is proposed that both the change of interface properties and the aggregation of particles contributed to flotation removal of particles. Longer reaction time and higher dosage were needed when n-dodecyl amine chloride (DAC) was used as a collector, owing to its relatively weak adsorption. The flotation efficiency increased with increasing DAC concentration. The improved flotation efficiency at pH of 10.0 was probably due to the formation of DAC precipitate.