本實驗研究目的主要為從含氟工業廢水中以形成類鈣鈦礦結構礦物之方式回收氟廢水(626.5 mg/L)，並探討不同平衡pH值、Na/F、Al/F莫耳比及氫氧化鉀(KOH)與氫氧化鈉(NaOH)兩種pH添加劑對其氟回收之影響。實驗結果顯示，利用不同pH添加劑NaOH和KOH可分別得到冰晶石(Na3AlF6, cryolite)與鉀冰晶石(K2NaAlF6, elpasolite)之沉澱物。當Na/F、Al/F莫耳比分別為12/6、1/6條件下且利用NaOH作為pH添加劑，在平衡pH值範圍為5.5到7.2時，氟的去除效率高於94.5%，當平衡pH大於7.6後，其氟去除效率大幅下降至78.0%。此外，晶相分析結果顯示，沉澱物除了冰晶石同時也包含副產物NaAlF4•0.83H2O與AlF2OH•1.4H2O。然而，藉由元素分析可知此程序在平衡pH條件為3.4至7.2範圍中，其主要沉澱物含量為冰晶石，成分濃度百分比並無明顯地受副產物影響。如將Al/F莫耳比提升至2.5/6，氟去除效率無法因此有效提升。同時，利用PHREEQC模擬軟體預測產物之組成和分佈並與實驗結果相互比較。另一方面，利用KOH調整廢水pH值與Na/F、Al/F莫耳比分別為3/6、1/6且平衡pH值為4.2至5.7的條件下，氟去除效率可高於94.7%且其沉澱物為鉀冰晶石。在粒徑量測與濁度分析實驗中，靜置5分鐘後，冰晶石與鉀冰晶其溶液濁度分別小於10NTU與2 NTU，顯示此程序具有良好沉降與分離效果。

This study aims to investigate the recovery of fluoride (626.5 mg/L) from an industrial wastewater in forms of perovskite-like minerals. Effects of equilibrium pH (pHeq), molar ratio of Na to F (Na/F), molar ratio of Al to F (Al/F), and different pH reagents were examined. Fluoride was recovered as cryolite (Na3AlF6) and elpasolite (K2NaAlF6) when pH of wastewater adjusted by NaOH and KOH, respectively. Once NaOH was used as pH reagent, fluoride removal efficiency was higher than 94.5% at Na/F of 12/6, Al/F of 1/6 and pHeq range of 5.5 to 7.2, but it decreased to 78.0% as pHeq became higher than 7.6. Although characteristic peaks of NaAlF4•0.83H2O and AlF2OH•1.4H2O showed in crystal patterns, it is noted that the amount of byproducts was insignificant from wet chemical analysis. Therefore, Na3AlF6 was the main precipitate recovered from wastewater at pHeq range of 3.4 to 7.2. However, increasing Al/F from 1/6 to 2.5/6, did not enhance removal efficiency at pHeq 5.5. PHREEQC simulation is conducted to predict and compare precipitation and speciation of Na3AlF6 with experimental ones. On the other hand, similar fluoride removal efficiency (>94.7%) was obtained using KOH as pH reagent at Na/F of 3/6 and Al/F of 1/6 when pHeq ranged from 4.2 to 5.7. As Na/F reduced to 1/6, it was obtained the lower fluoride removal efficiency except for pHeq 5.5. Morphology of precipitates recovered from wastewater was significantly affected by Na/F, Al/F and pHeq. Size analysis and sedimentation test showed that both K2NaAlF6 and Na3AlF6 could be easily separated from water.

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