薄膜電晶體液晶面板(TFT-LCD)製造業產生的廢水含有高濃度的氟及磷酸。此研究之目地為研究工業廢棄物合成之吸附材 – 鈣礬石，及其對氟離子與磷酸根離子之去除效果。此研究使用工業廢棄物為:鹼性氧氣轉爐（BOF）爐渣，煙氣脫硫（FGD）石膏和純硫酸鋁。此研究顯示摩爾比[鈣]:[鋁]:[硫酸根] = 3:2:3及平衡酸鹼值為11.74下為合成鈣礬石之最佳條件。工業廢棄物和合成鈣礬石以場發式掃描電子顯微鏡（FE-SEM）及X光繞射分析儀（XRD）分析。

動力學研究表明，氟離子與磷酸根離子吸附現象皆符合擬二階 (pseudo-second-order) 模型。實驗結果表明，當在低濃度時主要去除機制是表面沉澱與吸附，而在高濃度時為沉澱。羥基磷灰石（HAP）和氟磷灰石（FAP）為主要沉澱物，與XRD分析結果一致，也符合PHREEQC平衡預測。氟離子和磷酸根離子以1.0克/公升之鈣礬石最高去除量在25 °C，平衡酸鹼值範圍為10.89至12.42時分別為186.77毫克/克及613.33毫克/克，顯示鈣礬石對於氟離子及磷酸根離子具有良好去除能力。

The thin-film transistor liquid crystal display (TFT-LCD) industry generates effluents with high concentrations of fluoride and phosphate. The objective of this study was to investigate the removal efficiency of fluoride and phosphate using ettringite synthesized from industrial wastes. The industrial wastes used in this study were basic oxygen furnace (BOF) slag and flue gas desulfurization (FGD) gypsum. Addition of pure aluminum sulfate was also employed in the synthesis reaction. The molar ratio ([Ca]:[Al]:[SO4]) of 3:2:3 under pHeq 11.74 was found to be the optimum synthesis condition for ettringite in this study. The industrial wastes and synthesized ettringite were characterized by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) analysis.
Kinetics study indicated that both fluoride and phosphate adsorption obeyed pseudo-second-order rate equation. Experimental results showed that fluoride and phosphate were mainly removed by surface precipitation in combination with adsorption at low equilibrium concentration and by surface precipitation at high concentration. Hydroxyapatite (HAP) and fluorapatite (FAP) were the major precipitates formed in the removal process as analyzed by XRD, which was in good agreement with PHREEQC predictions. The highest removal capacity of fluoride and phosphate with ettringite dose 1.0 g/L at 25°C, pHeq ranged from 10.89 to 12.42 was 186.77 mg/g and 613.33 mg/g, respectively. The results implied that the ettringite could effectively remove fluoride and phosphate.

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