| Summary: | 碩士 === 國立臺灣科技大學 === 化學工程系 === 96 === e etching wastewater from thin film transistor liquid crystal display (TFT-LCD) manufacturers contains high concentration of phosphate. The aim of this thesis was to investigate the feasibility of phosphate removal from TFT-LCD wastewater by precipitation with calcium and magnesium salts. Optimal operating conditions were determined. Besides , field-emission scanning electron microscope (FE-SEM) and X-ray diffraction (X-RD) were used in characterization of precipitates.
Both pH value and molar ratio of metal to phosphate play important roles in precipitation of phosphate. For calcium salts, excess dosage resulted in higher removal efficiency of phosphate. However, the pH value must be controlled between 8.5 and 10.5. Magnesium salts showed lower removal efficiency when compared to calcium salts. Yet, they were more selective in phosphate removal when in the presence of fluoride.
The results of precipitate characterization showed that the dominant phase of calcium phosphates precipitates depended on the pH value. When at pH value of 5.5, the dominant phase was found to be dicalcium phosphate dihydrate (DCPD), while hydroxyapitite (HAP) predominantly formed between a pH of 6.5 and 10.5. It was observed that bobierrite was predominantly formed between pH of 8.5 and 10.5 when magnesium salts were used.
Result from the study indicated that the removal efficiency of phosphate by precipitation was satisfactory. Besides, the precipitates were potentially reusable as fertilizers. The method is promising for application on phosphate removal from TFT-LCD wastewater.
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