奈米零價鐵在飽和多孔介質中的傳輸模擬及管柱試驗

含氯有機物釋放至地下水多孔介質中易形成比水之重非水相液體 (Dense Non-Aqueous Phase Liquids, DNAPLs)。以奈米級零價鐵 (nanoscale zero valence iron，NZVI) 直接注入土壤地下水層或許可整治受污染之地下水層。由於奈米粒子之間的距離很小，顆粒間的吸引力使其極容易絮聚，而無法均勻分散於液相中，因此首先須利用界面活性劑作為表面修飾劑，增加顆粒表面電荷斥力或是空間阻隔力，使奈米粒子穩定。本研究利用三種不同的界面活性劑或聚合物，聚丙烯酸 (PAA)，月桂基醯乙二醇胺 (CDE) 或十二烷基硫酸鈉 (SDS) 修飾奈米零價鐵。以最終總鐵濃度1250 mg/L，修飾劑濃度PAA 1250 mg/L、CDE 2500 mg/L或SDS 1250 mg/L修飾過之奈米鐵懸浮液中，以PAA修飾者有最佳的殘留率82 %；CDE修飾者穩定性次之，有66 %的殘留率；SDS修飾者液穩定性最差，只有35 %的殘留率。再以穩定性較佳之奈米零價鐵懸浮液通過10 cm之填充石英砂之飽和多孔介質管柱，以PAA修飾者貫穿管柱濃度約為20 %；以CDE修飾者所得到的貫穿效果為最佳，貫穿濃度殘留率達到60 %；以SDS修飾者貫穿率只有12.5 %。本研究採用軌跡分析 (trajectory analysis method) 方法模擬顆粒在多孔介質中的傳輸並建立軌跡模式。以Wei和Wu在2010年提出的模式為基礎，直接運用牛頓第二運動定律描述顆粒受力移動的情況，再以Langevin 方程式計算膠體顆粒移動的軌跡。本研究與Wei和Wu模式的差別在於除了考慮凡得瓦爾力、電荷斥力及空間阻隔力外，本研究將另外考慮震盪結構力在顆粒上的作用。本研究假設顆粒通過壓縮管型 (constricted tube) 之收集器通道，並進而推算顆粒在多孔介質中過濾收集的效率 (collection efficiency)。以本研究之管柱試驗結果來驗證軌跡模式，模擬的結果以PAA修飾的奈米零價鐵考慮空間阻隔力，其模擬的收集效率值與實驗所得值僅相差0.042 %。以CDE及SDS修飾的奈米鐵考慮震盪結構力，前者模擬值與實際收集效率相差0.086 %；後者相差0.039 %。本研究所使用的軌跡模式能用於模擬不同種類的修飾劑修飾之奈米零價鐵顆粒在多孔介質中的傳輸。

關鍵字

奈米零價鐵；表面修飾劑；多孔介質；軌跡分析；傳輸模式

並列摘要

Dense non-aqueous phase liquids (DNAPLs) is sometimes formed when chlorinated hydrocarbons has been released into groundwater aquifers. The use of nanoscale zero valence iron (NZVI) to treat DNAPLs by direct injection to contaminated aquifer has been proven effective. Unfortunately, due to the exceedingly narrow distance between nanoparticles, the attraction force between each particle is so huge that they could easily aggregate into lumps and became hard to disperse. Recently, the use of surface modifier such as surfactant or polymer to enhance the stability and mobility of nanoscale particles in aquifer by increacing surface electrostatic forces or steric forces have become popular. For this reason, the objective of this research was to investigate the effects of three types of surfactant/polymers, which are: (1) poly acrylic acid, PAA. (2) cocamide diethanolamine, CDE. (3) sodium dodecyl sulfate, SDS, on the mobility and tendency to be collected of NZVI. The results demonstrated that when PAA and the total iron concentrations were both 1250 mg/L, the most stable suspension could be reached with 82% of particles remain in suspension. A less satisfactory result 66% of particles are properly suspended was reached when the concentration of CDE increases to 2500 mg/L and the concentration of total iron remains at 1250 mg/L. The worst particle dispersion phenomenon was observed with only 35% of patricles suspended when the final concentration of SDS and total iron were both 1250 mg/L. The amount of NZVI modified with PAA, CDE, and SDS, respectively, breaking through 10 cm saturated soil column were 20 %, 60 %, and 12.5 % of the originally input amount respectively. In addition, simulations of the NZVI transportation in saturated porous media were performed. The trajectory simulation algorithm was developed to describe the efficiency of a single collector to catch submicrometer particles moving through saturated porous media. Modification of Wei and Wu’s model, established in 2010, a constricted-tube model incorporating the van der Waals force, Brownian diffusion, electrostatic and steric repulsion force mechanisms, developed to predict the transportation and deposition of surface modified NZVI particles by Lagrangian trajectory analytical approach.The oscillatory structural force had been taken into consideration in the modified Wei and Wu’s model. The results from column tests were compared with the trajectory simulation results. The results indicate that simulation of PAA-modified NZVI with consideration of steric repulsion force are fairly consistent with experimental results with only 0.042% in variation. Simulation results of CDE-modified NZVI differ from experimental results with 0.086% while simulation results of SDS-modified NZVI differ with 0.039%. The results of research has shown that the modified model is able to describe the transportation of NZVI in a collector with various surface modification and to successfully predict the behavior of nanoscale particles moving through saturated soil columns.

並列關鍵字

nanoscale zero valent iron ； surfactant ； porous media ； trajectory analysis ； transport model

參考文獻

王郁翔. 2005. 穩定奈米零價鐵顆粒之製備及在多孔介質中之傳輸. 國立台灣大學碩士論文.

謝彩虹. 2008. 奈米級零價鐵懸浮液之製備及於土壤飽和層中傳輸模擬之研究. 國立台灣大學碩士論文.

Alessi, D. S., and Z. Li. 2001. Synergistic Effect of Cationic Surfactants on Perchloroethylene Degradation by Zero-Valent Iron. Environ. Sci. Technol. 35 (18):3713-3717.

Bell, N. S., J. Sindel, F. Aldinger, and W. M. Sigmund. 2002. Cation-Induced Collapse of Low-Molecular-Weight Polyacrylic Acid in the Dispersion of Barium Titanate. J. Colloid Interf. Sci. 254 (2):296-305.

Chandrasekhar, S. 1943. Stochastic Problems in Physics and Astronomy. Rev. Mod. Phys. 15 (1):1-89.

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奈米零價鐵在飽和多孔介質中的傳輸模擬及管柱試驗

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