| 摘要: | 大部分以氧化鐵製成之吸附劑，通常以細小粉末的形式存在或在實廠的應用上會於水溶液中產生膠凝狀或絮狀物，造成固液分離上之困難。近來，許多研究者多將氧化鐵負載於基質表面，以克服上述之問題。然而，基質上所負載之鐵含量非常少。本研究將甲殼素及氯化鐵混合並利用鹼性溶液製成富含鐵之Chitosan-Fe 複合物。
吸附劑之形狀、溶解度及chitosan、鐵含量之比例影響砷去除效率。根據文獻，Chitosan、Fe及NaOH濃度、針頭高度及交叉結合反應等五個因子可能會影響Chitosan-Fe複合物之形成及砷之去除效率，因此本研究將以部分因子試驗篩選重要因子。隨後利用中心組合設計法(CCD)及反應曲面法(RSM)將被篩選出之因子(chitosan及Fe濃度)對圓度(%)、鐵溶出率(%)及砷去除率(%)做迴歸模式。由於最適化牽涉到不同操作參數及效應（即圓度、鐵溶出率及砷去除率），而各效應的最適條件不盡相同，因此由三個指標 (圓度、鐵溶出率及砷去除率) 決定望想函數 (Derringer’s desirability function)，來尋求最適的操作條件。
在pH 7下對最佳成分之吸附劑模擬等溫及動力吸附模式。而等溫吸附模式符合Langmuir等溫吸附模式並從中可得到單層吸附容積為11.7233 mg/g的砷吸附量並發現反應過程較緩慢，約5小時才達到平衡，故推斷汙染物砷及吸附劑表面間為特定吸附，與比表面積無關。SEM分析顯示吸附劑表面極為平滑，並由BET值中得知比表面積為0.099m2/g，由此可證吸附容積與單位表面積之官能基位址有關，與比表面積無關。
Most adsorbents based on iron oxides are available as fine powders or are generated in-situ in aqueous suspension as hydroxide floc or gel, making separation of these adsorbents from treated liquid very difficult. Recently, several researchers have developed techniques for coating iron oxide onto the surface of substrates to overcome the problem of solid-liquid separation. However, the iron content on the coated substrates is very low. Instead of using coating techniques, in this study iron-rich chitosan-iron oxide composites were formed by mixing chitosan and ferric chloride solution with alkaline solution.
The shape, solubility of adsorbent and ratio of chitosan and iron oxides affect Arsenic (As(V)) removal efficiency. According to literatures, five factors, namely concentration of chitosan, Fe, and NaOH, height of the needle head, and the cross-linking reaction, might affect the formation of chitosan-iron oxide composites and As(V) removal efficiency were tested, and their significance were screened experimentally according to fractional factorial design. Subsequently, the selected influential variables (Fe and chitosan concentrations) were included in the regression models of Aspect ratio (%), Solubility of Fe (%), and As removal efficiency (%) which were determined by CCD and RSM. The formula for making ‘the best’ adsorbent was determined based on Derringer’s desirability function including Aspect ratio, Solubility of Fe, and As Removal efficiency.
Adsorption of arsenic (V) by adsorbent produced using ‘the best’ formula was studied at pH 7.0 under equilibrium and dynamic conditions. The monolayer adsorption capacity obtained from fitting experimental data with Langmuir model was 11.72 mg/g, and the time to reach equilibrium is about 5 hours, indicating a specific adsorption occurring between the arsenic species and the surface of the adsorbent. SEM analysis reveals that the surface of adsorbent was smooth. |
