Adsorption of Fluoride, Chloride, Bromide, Sulfate and Nitrate onto Novel Superparamagnetic Zirconia from Aqueous Solutions

本研究以新穎超順磁性二氧化鋯吸附劑吸附處理含F-、SO42-、Cl-、Br-和NO3-水溶液。研究內容包含吸附劑之製備(分別以沈澱法(MZHP)及溶膠-凝膠法(MZSG)合成超順磁性二氧化鋯)、物理化學特性鑑定分析、等溫吸附行為、吸附動力及二氧化鋯吸附再生試驗。此外，亦針對操作因子如pH值、離子強度及陰離子初始濃度對鋯離子溶出之影響進行探討。
超順磁性二氧化鋯之製備程序乃先以共沉澱法製備奈米級Fe3O4超順磁性顆粒；再以溶膠凝-膠法於Fe3O4表面包覆SiO2，製得SiO2/Fe3O4磁性載體；最後再分別以沈澱法(MZHP)及溶膠-凝膠法(MZSG)於磁性載體表面上合成奈米級磁性二氧化鋯吸附劑。然而無法以沈澱法製得均勻之MZHP，因此以下之探討皆以MZSG為主要對象。Fe3O4、磁性載體及MZSG之飽和磁化強度分別為56.45、21.72及7.10 emu g-1，皆具有超順磁性。Fe3O4磁性顆粒粒徑約為7-9 nm，SiO2/Fe3O4磁性載體及MZSG粒徑約為10-12 nm。X射線繞射(X-ray diffraction, XRD) 之鑑定結果顯示MZSG表面之氧化鋯為四方晶體(tetragonal)及單斜晶體(monoclinic)結構。
等溫吸附試驗之結果顯示以Langmuir與Freundlich等溫吸附方程式皆能有效的描述MZSG吸附劑吸附氟離子及硫酸根之行為。以單層飽和吸附量(qL)及異質性(nF)而言，MZSG對氟離子吸附效果最佳。MZSG吸附反應速率非常快，且對pH值非常敏感，故以簡單設備(完全攪拌反應槽及氟選擇性電極)無法探討其對陰離子吸附的動力。

半導體實廠模擬廢水(實驗條件為配製 F-、SO42-、Cl-、Br-和NO3-初始濃度值分別為 54、2、2.2、1.1及10 mg L-1且初始pH值為4之水溶液)之混合陰離子吸附去除試驗。結果顯示：MZSG吸附可有效去除半導體廢水中之氟離子，對於其他陰離子(SO42-、Cl-、Br-和NO3-)而言，其吸附去除效果較差。
MZSG對氟離子之吸附再生試驗，以吸附、物理脫附、再生及中和程序為一循環。當處理水溶液pH值為4，重複4循環之後，則吸附容量為原來之83 %；而當處理水溶液pH值為5，重複8循環之後，則吸容量為原來之84 %。

Two novel magnetic zirconia adsorbents were synthesized employing precipitation (called MZHP) and sol-gel (called MZSG) methods, respectively, in this study. However, only MZSG possessed homogeneous property so that MZSG was the main adsorbent discussed in this study. MZSG was prepared with three sequentical steps: formation of Fe3O4 (magnetitie) as magnetic core via precipitation method; coating of SiO2 (silica) film on magnetite as magnetic carrier with sol-gel method; coating of ZrO2 as magnetic adsorbent via sol-gel method.
The physicochemical characteristics of adsorbents, adsorption behavior of various anions, such as F-, SO42-, Cl-, Br- and NO3-, and regeneration processes of aged adsorbents from fluoride adsorption were investigated. In addition, effects of operating parameters, such as ionic strength, pH value and initial concentration were also were also examined.
Langmuir and Freundlich isotherms can well describe the adsorption of F- and SO42- on MZSG from solutions, and MZSG possessed high potentical to remove F- and SO42-. However, the adsoption capacities of Cl-, Br- and NO3- were considerably low. There sults indicated MZSG was a good adsorbent for selective adsorption of F- and SO42-.