Treatment of Fluoride-Containing Wastewater of Semiconductor Manufacturer

• Main Authors: Chang Ming-Fa, 張明發
• Other Authors: J.C. Liu
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/85178362460370772217

碩士 === 國立臺灣科技大學 === 化學工程系 === 91 === The major objective of this study was to investigate coagulation- flocculation, recycling calcium fluoride sludge, and ultrafiltration in treating fluoride-containing wastewater from semiconductor manufacturer. Chemical precipitation method utilizing calcium salts is extensively used to treat fluoride-containing wastewater. The fine precipitates of calcium fluoride are further flocculated by PAC(polyaluminum chloride) and anionic polyelectrolyte to facilitate better solid-liquid separation. When molar ratio of calcium to fluoride was 0.5, the residual fluoride concentration could meet effluent limit of 15 mg/l. Experimental results indicated that both PAC and PAA(polyacrylic acid, M.W.=90,000) could remove CaF2 precipitate, represented as turbidity, effectively. Satisfactory turbidity removal was also achieved at lower dosage when PAC and PAA were used in combination. Upon recycling calcium fluoride precipitates or sludge, particle size of calcium fluoride did not grow apparently and neither residual fluoride concentration nor residual turbidity became lower. Sludge recycle did not prove to be a feasible method, as claimed by previous studies. Effects of operation pressure and crossflow velocity were investigated in ultrafiltration with and without coagulation pretreatment. Experimental results indicated that permeate flux and steady flux increased with increasing operation pressure and crossflow velocity. Initial flux and steady flux became higher after pretreatment by PAC or PAA. Field emission scanning electron microscope (FESEM) was used to observe filtration cake. Fouling mechanisms were discussed.