| Summary: | 碩士 === 國立臺灣科技大學 === 化學工程系 === 107 === The proposed study aims to develop a novel treatment technology for phosphate and ammonium-containing wastewaters from electronics industries to produce high- purity struvite. Combining ammonia-containing wastewater phosphate-containing wastewater from an identical source, it will be dosed with magnesium chloride to induce precipitation of magnesium ammonia phosphate (MgNH4PO4, struvite), a potentially reusable mineral. Experimental results indicated that when molar ratio of [PO4-3]:[Mg2+]:[NH4+] of 1:1:1 and pH 9, phosphate were removed 80~90 % at initial phosphate concentration from 1,000 to 20,000 mg/L. Moreover, when initial phosphate concentration increased, the morphology of the obtained products was shifted from rod-shaped to a fine particle. Therefore, it could be concluded that initial phosphate concentrations was a critical parameter and there was a strong correlation between particle size and morphology. The formation of struvite, as produced under different reaction conditions, were confirmed by FESEM, XRD, and wet chemical analysis. Theoretical equilibria were modeled with PHREEQC and compared with experimental results. A pilot scale system consisting of a 10-dm3 reactor was used. Not only the volume of wastewater was from 500 ml to 10 L, but also industrial grade chemicals were used. The scale-up system was evaluated for potential applications in the factory. However, recovery of phosphate as magnesium phosphate, the effluent cannot meet of effluent standards of Taiwan EPA. To ensure effluent quality, a 2-stage in-series precipitation unit is proposed in which calcium chloride is added to induce the formation of hydroxyapatite (Ca5(PO4)3OH).
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