螯合離子交換與電解薄膜混合程序去除重金屬離子之最佳化

Optimization for the Removal of Heavy Metals Using a Hybrid Chelating Ion-Exchange and Electrolytic Membrane Process

林麗君(Li-Chun Lin)

指導教授 ： 莊瑞鑫

元智大學/工程學院/化學工程與材料科學學系/博士(2007年)

https://doi.org/10.6838/YZU.2007.00283

摘要

要從給水或廢水中去除重金屬離子的方法很多，其中以離子交換是最簡單和有效率的。本研究選用含有亞胺二醋酸鹽 (Iminodiacetate, IDA) 官能基的螯合劑 (Chelating) 之螯合交換樹脂 Amberlite IRC 748來去除模擬廢液中Cu2+ 和Ni2+。首先在IRC 748與Cu2+ 和Ni2+ 批次交換研究裡，因IRC 748的官能基IDA結構與pH值有關，在低的pH值會傾向與H+ 結合成分子結構，降低了交換Cu2+ 和Ni2+ 的能力，當pH值在4附近時，IDA會解離，故交換Cu2+ 和Ni2+ 的機會就增加，則去除Cu2+ 和Ni2+ 的效果就愈好，故IRC 748樹脂要能與Cu2+ 和Ni2+ 有不錯的交換效果，pH值最好有4以上。同理，要溶出交換至IRC 748樹脂上的Cu2+ 和Ni2+，則水溶液中的pH值愈低，溶出效果就愈好。此外，在批次交換的動力研究裡，實驗顯示交換反應動力學受孔隙擴散所限制，我們並由此得知在25oC時，IRC 748與Cu2+ 、Ni2+ 、Cu-EDTA與Ni-EDTA的交換之平均有效擴散係數 (DM) 分別是1.64 × 10-10 、1.04 × 10-10、5.85 × 10-11與4.19 × 10-11 m2/s，而以EDTA自IRC 748樹脂中溶出Cu2+ 與Ni2+ 的平均有效擴散係數 (DM) 分別是1.20 × 10-9 與1.76 ×10-9 m2/s。由平衡與動力學資料，我們得知其符合Langmuir等溫式，在交換時為一吸熱反應，求得之IRC 748與Cu2+ 及Ni2+ 的 ?寒0 值分別為23.68及28.81 kJ/mol，以Pitzer法所求得Cu2+ 及Ni2+ 的熱力學平衡常數實驗值各為7.53 × 10−3及3 × 10−3。
固定床樹脂的交換實驗是在不同的金屬濃度 (10-100 mol/m3)，以及體積流量 (1-10 cm3/min) 下進行，並藉著由兩個參數組成的Thomas模式探討其貫穿動力學。固定床樹脂再生實驗，則以EDTA與HCl為主，並加以比較。由貫穿曲線實驗我們得知，不論是交換或溶出實驗均是以向下流之同流式方式效果較佳。在我們L/D 為 20及填充0.0075 kg的樹脂情況下，流速及濃度最好控制在3 cm3/min 及60 mol/m3下，可將廢水處理至零的目標，符合嚴格的環保法規。
最後我們利用電化學薄膜法來回收Cu2+ 與螯合劑EDTA，其陰極液Cu-EDTA是先由以定流量3 cm3/min的100 mol/m3之模擬Cu2+ 流經0.0075 kg之樹脂床後，再以定流量3 cm3/min但不同濃度的溶出劑EDTA自樹脂中將Cu溶出。研究的方法為以此錯合離子溶液作為對象，使用自製的直流電源供應器電解Cu-EDTA，在不同的電流密度、錯合離子溶液之濃度與pH值等條件下，測試Cu2+ 與EDTA之回收率和電流效率的情形。由研究結果得知，電解Cu-EDTA，最佳的pH在2.2附近。若在相同的時間與定電流密度操作下，將Cu-EDTA的濃度提高，電流效率及Cu與EDTA的回收量也會提高。

關鍵字

離子交換, 螯合樹脂, 電解薄膜程序

並列摘要

There are lots of methods to remove the heavy metal ions from supply water or wastewater, while ion exchange is the most simple and efficient one. In this study, Amberlite IRC 748, containing the chelating ligand of functional group iminodiacetate (IDA), was used to remove Cu2+ and Ni2+ from the simulating wastewater. First, in the study of batch exchange of IRC 748 with Cu2+ and Ni2+ , the structure of the functional group IDA of IRC 748 is dependent on a pH value of solution, i.e., IDA tends to combine with H+ to become a molecular structure at low pH value, which reduces the exchange capacity with Cu2+ and Ni2+, when pH value is raised to about 4, IDA will be decomposed, and the exchange capacity with Cu2+ and Ni2+ will be increased, thus improves the effect of removing Cu2+ and Ni2+. So, the better effect of exchange between IRC 748 with Cu2+ and Ni2+ occurs at pH value above 4. Conversely, the lower the pH value, the better the extract effect of Cu2+ and Ni2+ exchanged to IRC748. Besides, in the kinetic experiment of batch exchange, it shows the exchange kinetics is limited by the pore diffusion, and it is obtained that at 25oC, the mean effective diffusion coefficient (DM) of exchange of IRC 748 with Cu2+, Ni2+, Cu-EDTA, and Ni-EDTA is 1.64 × 10-10, 1.04 × 10-10, 5.85 × 10-11 and 4.19 × 10-11 m2/s respectively, and the mean effective diffusion coefficient (DM) of extraction of Cu2+ and Ni2+ from IRC 748 using EDTA is 1.20 × 10-9 and 1.76 ×10-9 m2/s respectively. From the data of equilibrium and kinetics, it shows the exchange reaction obeys the Langmuir isotherm and is an endothermic reaction, the ?寒0 of exchange of IRC 748 with Cu2+ and Ni2+ is 23.68 and 28.81 kJ/mol respectively, and the thermodynamic equilibrium constants of Cu2+ and Ni2+ obtained by using Pitzer's method are 7.53 × 10−3 and 3 × 10−3.
Fixed-bed experiments were carried out at various concentrations of metal ions (10-100 mol/m3) and at various volumetric flow rate (1-10 cm3/min), and the exchange kinetics were studied by using the two-parameter Thomas’s model. Fixed-bed resin regeneration experiments were carried out mainly by using EDTA and HCl and make a comparison. From the breakthrough curve experiment, it shows that the experimental effect is better by the co-current down-flow, either exchange experiments or extraction experiments. Under the L/D value of 20 and the resin weight of 0.0075 kg, the flow rate and concentration is best controlled at 3 cm3/min and 60 mol/m3, the wastewater treatment can be attained to "0" effluent, to match the serous environmental protection rules.
In the experiment of recovering Cu2+ and chelating agent EDTA by the electrochemical membrane method, first, let the simulating Cu2+ solution (100 mol/m3) flow into 0.0075 kg resin bed at constant flow rate of 3 cm3/min, then use various concentrations of eluting agents EDTA at constant flow rate of 3 cm3/min to elute Cu from the resin, this complex ion solution is called the catholyte solution Cu-EDTA of electrochemical membrane process. In this study, Cu-EDTA is electrolyzed by using the self-made DC power supply at various current densities, concentrations of complex ion solutions and pH values, to test the effect of current efficiency on Cu2+ and EDTA. From the result, it shows that the optimum pH value is c.a. 2.2 while electrolyzing Cu-EDTA. If the experiment is carried out under the same time and constant current density, when the concentration of Cu-EDTA is raised, the current efficiency and the recovery of Cu and EDTA will be thus increased.

並列關鍵字

Ion-Exchange, Chelating resins, Electrolytic Membrane Process

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