| 摘要: | 零價鐵已被證實為經濟便宜、對環境友善、較無不良副產物產生，適宜應用於地下水體中整治去除污染物。最理想之零價鐵應用技術為現地注入奈米級零價鐵至受污染地下水層，讓奈米級零價鐵隨地下水流移動至污染團中發揮效能，但主要應用限制為奈米級零價鐵會因凡得瓦爾力及磁性產生凝聚及膠凝作用使零價鐵粒徑變大、發生沉澱作用或因過濾作用而阻滯於地下含水飽和孔隙層，使移動傳輸距離變短。如能藉由添加表面修飾劑，維持奈米級零價鐵在含水土壤層孔隙間保持奈米級顆粒分散穩定狀態，將可提升奈米級零價鐵在野外場址整治去除污染物之實用性。
本研究使用單一型表面修飾劑(SDBS、SDS、CMC、PAA、PEI、PVG、PVP、PSS、alginic acid、sodium alginate及gelatin)及混合型表面修飾劑(CMC混合PAA)，維持還原法合成之零價鐵顆粒分散性，探討在各種濃度表面修飾劑作用下合成之零價鐵粒徑特性，包括粒徑大小、分佈、界達電位及受離子強度(Ca2＋、Na＋)之影響；並探討奈米級零價鐵在模擬含水飽和石英砂管柱中移動性受表面修飾劑之影響。實驗結果發現CMC、PAA、Sodium alginate及PSS表面修飾劑有穩定分散零價鐵顆粒效果，使合成零價鐵顆粒粒徑分別達到奈米級尺寸6.3、5、6及20.8 nm；與未添加分散劑之零價鐵顆粒比較，其穿透砂層孔隙效能高出26.47、24.47、29.91及9.73倍。採用4×10-6 M CMC＋1.26×10-3% PAA混合表面修飾劑可使零價鐵顆粒數量比平均粒徑達16.1 nm。添加單一型(0.0063% PAA、2×10-6 M CMC)或混合型(0.0063% PAA+4×10-6 M CMC)表面修飾劑，於還原生成零價鐵前或後增加懸浮液中Ca2＋、Na＋離子強度，膠體顆粒表面之負電荷將被相反電荷抵消，使零價鐵顆粒相互吸引凝聚增加顆粒尺寸。
The direct injection of zerovalent iron (ZVI) nanoparticles into the contaminated subsurface aquifer has attracted interests in recent years such as direct decontamination of polluted plume in groundwater zone, environment friendly, and reducing remediation cost. However, the synthesized ZVI nanoparticles with sodium borohydride could aggregate quickly with van der waals or magnetic forces from nano scale into micro scale or larger and attracted in the soil surface layer when it were transported through the soil holes. To improve the migration distance and prevent the aggregation of ZVI nanoparticles, surface modifiers are used to reduce the ZVI nanoparticles sizes, to stabilize the ZVI nanoparticles and to enhance the transportation efficiency through groundwater layer.
Single type surface modifiers (SDBS, SDS, CMC, PAA, PEI, PVG, PVP, PSS, alginic acid, sodium alginate and gelatin) and mixed type surface modifiers (CMC mixed PAA), have been employed to maintain the dispersion of ZVI particles which were prepared with borohydride reduction method of ferric ion. Dynamic light scattering (DLS) analyses, UV-vis spectrophotometry, and zeta potentiometry are used to characterize the ZVI nanoparticles which were disperzed with various concentrations of surface modifiers at different pH. The effects of ionic strength (Na＋, Ca2＋) on NZVI dispersion in suspension and the migration efficiency of stabilized ZVI through sand column were also discussed. CMC, PAA, Sodium alginate, and PSS could modify, reduce and disperse the ZVI nanoparticles into 6.3, 5, 6, and 20.8 nm in diameters, respectively. Comparison with bare ZVI particles without modification of surface modifiers, the migration efficiency of stabilized ZVI through water saturated sand column, increased as high as 26.47, 24.47, 29.91, 9.73 times for CMC, PAA, Sodium alginate, and PSS, respectively.
Mixed surface modifier (4 × 10-6 M CMC +1.26 × 10-3% PAA) can disperse the ZVI particles in average number-weighted particle size of 16.1 nm. Dispersion with single (0.0063% PAA, 2 × 10-6 M CMC) or mixed surface modifiers (0.0063% PAA +4 × 10-6 M CMC), the addition of ionic strength (Ca2 + and Na+) will aggregate the ZVI nanoparticles into larger size, no matter what the addition of sodium borohydride before or after the Ca2 + and Na+。 |
