| 摘要: | 為提升大麥萃取殘渣吸附去除水中重金屬離子的商品應用價值及效能，本研究以四種化學修飾法(包括磷酸鹽修飾法、檸檬酸修飾法、硫代硫酸鈉修飾法及甲醛修飾法)，配合硫脲架橋作用，修飾大麥萃取殘渣製成九種吸附劑，進行重金屬離子(Cu(Ⅱ)、Pb(Ⅱ)、及Zn(Ⅱ))批次吸附試驗，可同時處理食品加工廢棄物和移除廢水中重金屬離子，有益於提高廢棄物減量及再利用價值，更有助於永續環境利用。本研究探討影響吸附劑吸附重金屬離子之參數：如pH值、接觸時間、反應溫度、重金屬離子種類、混合重金屬離子之相互吸附競爭、及重金屬離子濃度等，並以等溫吸附平衡方程式、吸附動力學及吸附熱力學平衡模式來探討吸附效能。
比較各種經修飾化吸附劑對Cu(Ⅱ)、Pb(Ⅱ)、及Zn(Ⅱ)於最佳操作條件下吸附量為10.92、10.02、及9.21 mg/g；最差吸附量為3.08、4.07、及5.02 mg/g；最佳吸附pH為4.5～7.0。吸附反應穩定平衡時間約為60分鐘。以 Freundlich、Langmuir及Dubinin–Radushkevich equation三種等溫吸附平衡模式套用於等溫吸附平衡實驗數據，可計算各種吸附劑等溫吸附平衡常數及判斷屬於物理性或化學性吸附行為。以三種吸附動力模式( Pseudo first–order rate、Pseudo second–order rate 及 Intraparticle diffusion equation)評估發現Pseudo second–order rate equation 最適於描述修飾化吸附劑之吸附動力行為。由吸附熱力學特性參數（標準自由能（△Go）、焓值（△Ho）、及熵值（△So）變化）顯示吸附反應溫度從 15℃增至 70℃時，吸附Cu(Ⅱ)、Pb(Ⅱ)、及Zn(Ⅱ)反應主要為吸熱之自發性反應。在混合重金屬離子溶液中，受三種重金屬離子相互競爭吸附位置影響，吸附動力行為亦適合以Pseudo second–order rate equation描述，吸附熱力學特性亦主要為吸熱之自發性反應。
Four chemical modification methods were used to modify barley residual into adsorbent, including phosphorylation, sulfonation, sodium thiosulfate, citric acid, and formaldehyde modification. Those were used to increase the adsorption capacity of heavy metals compared with bare barley residual. The solid waste reduction and reuse at food processing plant could be promoted and the heavy metal ions could be removed from waste water in the same time. It is helpful and sustainable utilization of environmental resources. The adsorption capacity of heavy metal ions (Cu(Ⅱ), Pb(Ⅱ), and Zn(Ⅱ)) onto adsorbents was characterized by pH, contact time, contact temperature and heavy metal ions. The adsorption experimental data also evaluated with isothermal adsorption, adsorption dynamic and adsorption kinetic models.
The highest adsorption capacity of Cu(Ⅱ), Pb(Ⅱ)and Zn(Ⅱ) onto bare and modified adsorbents were 10.92, 10.02, and 9.21 mg/g, respectively. The lowest adsorption capacity for Cu(Ⅱ), Pb(Ⅱ) and Zn(Ⅱ) were 3.08, 4.07 and 5.02 mg/g, respectively. The optimum operation pH ranged between 4.5~7.0. 60 minutes was needed to reach equilibrium state of adsorption.
Three isothermal adsorption equations, Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) were used to evaluate the isothermal adsorption constants from experimental data and to judge the chemical or physical adsorption. The pseudo-second order rate equation fitted excellently the description of dynamic adsorption behavior of heavy metal ions (Cu(Ⅱ), Pb(Ⅱ) and Zn(Ⅱ)) onto adsorbents than the pseudo first-order rate, and intraparticle diffusion equation. The variations of thermodynamic parameters (free energy change (ΔG0), enthalpy change (ΔH0), entropy change (ΔS0)) indicated that the adsorption of Lead (II), Zinc (II) and Copper (II) was primarily endothermic process and the adsorption capacity increase with increasing temperature from 15 to 70 ℃.
Under the competition of other heavy metals onto the adsorptive sites in adsorbents, the adsorption behavior of heavy metal ion also fitted excellently the pseudo-second order rate equation and the calculated thermodynamic constants also indicated primarily the endothermic and spontaneous adsorption process. |
