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    Please use this identifier to cite or link to this item: http://tkuir.lib.tku.edu.tw:8080/dspace/handle/987654321/94571

    Title: 以冰晶石結晶方式從含氟廢液中回收氟之研究
    Other Titles: Recovery of fluoride from fluoride-containing wastewater by cryolite crystallization
    Authors: 林智偉;Lin, Chih-Wei
    Contributors: 淡江大學水資源及環境工程學系碩士班
    Keywords: 含氟廢水;冰晶石;結晶;luoride-containing wastewater;cryolite;Crystallization
    Date: 2013
    Issue Date: 2014-01-23 14:46:55 (UTC+8)
    Abstract: 半導體業之氟系廢水處理仍以添加鈣鹽,產生氟化鈣(CaF2)為主,處理過程中會產生大量高含水率的污泥。雖然上述傳統處理流程可將氟離子濃度降至法定排放標準(<15 mg/L),但目前台灣面臨現有的掩埋空間明顯不足,導致污泥廢棄置成本大幅提高,因此亟需思考其他可行的處理方式。
    Changing fluoride solubility in solution with addition of calcium salt to precipitate calcium fluoride solid is the most common practice to treat fluoride wastewater generated from semiconductor industry. As the result, large volume of sludge with high water content was produced. Although the above-mentioned traditional treatment process is capable of lowering fluoride concentration below the regulatory discharge limit of 15 mg/L in Taiwan, alternative treatment process is needed due to substantial increase in sludge-handling cost associated with limited landfill space.
    In this study, various aluminum salts were used as aluminum source for the synthesis of cryolite by crystallization in the hope of removing, recycling, and reusing fluoride from fluoride-containing wastewater. Several process parameters such as initial concentration of fluoride, Al/F and Na/F molar ratios, pH, temperature, reaction time and anionic concentration which might affect fluoride removal efficiency were investigated in Jar-Test experiments.
    The results showed that synthetic cryolite was formed effectively within appropriate Al/F molar ratio and pH ranges and fluoride recovery efficiency of up to 89% could be achieved. Excessive addition of aluminum ions with Al/F ratios of higher than 1/6 leads to formation of gelatinous aluminum hydroxide which will affect the purity of synthetic cryolite. Addition of different aluminum salts achieved different fluoride removal efficiency due to the attraction of aluminum ions with various anions which is in the order of F- > SO42- >> Cl- > NO3-.
    Recovery of fluoride by cryolite crystallization was conducted with wasted hydrofluoric acid obtained from an optoelectronic manufacturer. Aluminum salt added stepwisely was more effective than addition of aluminum salt at once for producing synthetic cryolite and removing fluoride. The precipitates solids contain cryolite (Na3AlF6), chiolite (Na5Al3F14), fluorine sodium silicate (Na2SiF6) confirmed by XRD analysis. Cares should be exercised when adding caustic soda to adjust pH of wasted hydrofluoric acid. Heat will be generated due to exothermic nature of the reaction.
    Appears in Collections:[水資源及環境工程學系暨研究所] 學位論文

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