Adsorption of lead, cadmium, copper, zinc, and nickel, by surfactant modified goethite.


針鐵礦因為實驗室合成的便利性及良好的結晶特性,已成為研究各種界面(或表面)吸附現象與機制以及水體污染物之移除時備受廣泛使用的吸附材質之一。但是受制於其表面電荷之特性,常使得針鐵礦在一般水體環境條件下吸附正電性金屬物種(微量金屬或重金屬)的功效受到限制。界面活性劑是一種兩性分子,分子組成中各有極性端(或稱親水端,為頭部)與非極性端(或稱疏水端,為尾部),經常用於土壤或地下水有機污染物復育的實驗室研究及現地場址之試驗;界面活性劑藉由覆蓋表面或插入層間,為固體吸附劑增加疏水性甚至轉變表面電性所構成的修飾性吸附材料則屬於另一種應用方式。本研究即是利用陰離子性界面活性劑(SDS)修飾針鐵礦表面,以希望提高表面負電荷來增加金屬吸附量為出發,探討修飾對針鐵礦吸附重金屬的影響。研究結果說明了金屬吸附量確實受表面負電荷增加而有所提升,而且推論負電荷及其於金屬吸附量之效應乃透過界面活性劑於表面之局部雙層結構所貢獻。各樣品對金屬的等溫吸附結果與Langmuir model有良好的配適,數據顯示SDS修飾提高了針鐵礦吸附重金屬的最大吸附容量(qmax),以Cd、Zn尤甚;對Cd、Zn之吸附親和力(KL)亦從無到有,最高對Pb可提升將近5倍之多,對Cu提升約79 %,對Ni則提升約95 %。DRIFT光譜分析之結果,則幫助我們更加確認針鐵礦表面修飾結構之存在。由本研究的實驗成果加上其他眾多的研究文獻,相信此類吸附劑之修飾技術於環境污染復育上應尤有可為。Because of well crystalline and ease for synthesis in laboratory, goethite has become one of the most widely used adsorbents for researching phenomena and mechanisms of varied adsorbates adsorbed on the surface/interface, and also for removing contaminant in aquifers. In general condition of the aqueous environment, however, goethite is usually limited to adsorb trace metal or heavy metal species by its characteristic of surface charge. Surfactants with both polar (hydrophilic) and nonpolar (hydrophobic) group in molecular constitution has been used in the remediation of soil or groundwater organic contamination in laboratory scale as well as in situ trial works. It was also shown that solid adsorbents are able to become more hydrophobic and to reverse the surface charge through the surfactant modification. In this study, our intent is to promote the adsorption for heavy metals by goethite via such kind of modification. We took advantage of the negatively charged anionic surfactant (sodium dodecyl sulfate, SDS) to modify the surface of goethite, and investigated the effect of different proportional modifications on the capability of adsorption for heavy metals by goethite. The amount of metals adsorbed on the solid sample was significantly promoted by the SDS modification. It could be speculated that the partial bilayer structure of surfactant on goethite surface was responsible for additional negative charges and its influence on metal adsorption as well. Adsorption isotherm data were well fitted with Langmuir model. It showed that the SDS modification raised the maximum adsorption capacity (qmax) of goethite for heavy metals, especially for Cd and Zn. The adsorption affinity (KL) was also enhanced by modification, up to five times in increase for Pb, 79% and 95% in increase for Cu and Ni respectively, and Cd was helped to grow out of nothing as well as Zn. According to the DRIFT analysis, we were convinced of the existence of the modification arrangement. By plenty of previous research coupled with this study, one can believe that such technique of modified adsorbents will get an advance in the remediation of environmental contaminations.謝誌---------------------------------------------------------------- i 摘要-------------------------------------------------------------- iii 英文摘要------------------------------------------------------------ v 目錄--------------------------------------------------------------- vi 表目錄----------------------------------------------------------- viii 圖目錄------------------------------------------------------------- ix 第壹章 前言--------------------------------------------------------- 1 一、 針鐵礦與重金屬吸附-------------------------------------------- 1 二、 界面活性劑基本性質與分類--------------------------------------- 2 三、 界面活性劑與土壤及地下水污染----------------------------------- 6 四、 界面活性劑修飾性材料之發展與應用-------------------------------- 8 五、 等溫吸附模式------------------------------------------------ 12 六、 Visual Minteq程式------------------------------------------ 15 七、 研究目的---------------------------------------------------- 16 第貳章 材料與方法----------------------------------------------------17 一、 鐵礦之合成---------------------------------------------------17 二、 合成樣品之鑑定與特性分析---------------------------------------18 三、 針鐵礦之表面修飾----------------------------------------------20 四、 重金屬等溫吸附實驗--------------------------------------------23 五、 pH對重金屬吸附之效應------------------------------------------24 第參章 結果與討論----------------------------------------------------26 一、 針鐵礦與界面活性劑(SDS)之吸附--------------------------------26 二、 合成針鐵礦之基本特性------------------------------------------32 三、 pH對重金屬吸附之效應------------------------------------------45 四、 重金屬之等溫吸附實驗------------------------------------------55 五、 修飾針鐵礦之FTIR分析------------------------------------------74 第肆章 結論-------------------------------------------------------81 第伍章 參考文獻----------------------------------------------------83 附錄----------------------------------------------------------------8

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