利用奈米零價鐵粉處理受鉻污染水體之研究

Remediation of Chromium-Contaminated Water by Using Zero-Valent Iron Nanoparticles

張貴錢(Chang Kuei-Chien)

指導教授 ： 林錕松

元智大學/工程學院/化學工程與材料科學學系/碩士(2003年)

摘要

國內水體受重金屬污染十分嚴重，同時造成人體危害及環境之衝擊。本研究之奈米零價鐵粉是由化學還原法製備，主要目的是探討奈米零價鐵粉吸附三價或六價鉻溶液後之變化與結構分析。經由同步輻射XANES分析奈米零價鐵粉對於六價鉻是進行氧化還原反應將其還原成三價鉻；相較於三價鉻並未有價數上之改變，意味著只是吸附於鐵粉表面，可能進行不明顯的還原作用。其反應的可行性可由電化學反應式所推導出來。由吸附動力結果顯示為一擬一階反應(pseudo-first-order )，並可求出基準化速率常數（kSA）為0.0124 min-1m-2 g及半衰期t1/2為1.32 min。經由等溫吸附平衡實驗的測定後，可找出奈米零價鐵粉吸附六價鉻後以Freundlich為最佳的吸附模式；而相較於三價鉻則以modified Langmuir描述最為適用。FE-SEM及XPRD顯示吸附鉻之鐵粉微粒可能為氧化鐵，結構成鬆散狀。本研究亦是典型應用同步輻射光源及原子級分析光譜，研究奈米鐵微粒吸附毒性鉻金屬及其在表面吸附之氧化還原反應之實例。其經由EXAFS光譜顯示吸附三價及六價鉻之奈米零價鐵粉微粒上之鉻還原成Cr2O3；相較於零價鐵是變成Fe2O3。由於奈米零價鐵粉對於含鉻污染物之去除具有高活性且已有初步成效，故希望未來應用於重金屬污染場址之現址復育（in-situ remediation）技術。

關鍵字

奈米零價鐵粉 ； 鉻污染物 ； borohydride還原反應 ； 吸附動力學 ； 表面分析 ； X光吸收近邊緣結構 ； 延伸X光吸收精細結構

並列摘要

Since chromium (III, VI) species are known to be toxic and carcinogenic, site remediation is necessarily required in order to reduce the risk to humans and ecosystems. Remediation of groundwater contaminated with Cr species by using zero-valent iron nanoparticles has received considerable attention in recent years. Therefore, the main objectives of the present study were to investigate the destruction and removal efficiency (DRE) and the adsorption kinetics of Cr (III, VI) aqueous solutions on the nanophase zero-valance iron.
Experimentally, nanoscale zero-valent iron particles of this study were prepared by borohydride reduction method at room temperature and ambient pressure. The DRE of Cr(III, VI) aqueous solutions on Fe(0) nanoparticles was ＞90% of average in the wide range (500 —5000 ppm) of the Cr concentrations. Adsorptive kinetics of the redox reaction from adsorptive equilibrium isotherm experiments of Cr(III, VI) aqueous solutions on Fe(0) nanoparticles can be satisfactorily described by the corresponding pseudo-first-order rate equation: -dC/dt = kSA A [C] = 0.524 [C]. The reaction rate constant normalized to 1m2 iron surface area (kSA) and reaction half life (t1/2) were 0.0124 min-1m-2 g and 1.32 min, respectively. In addition, the best adsorptive models for Cr(III) and Cr(VI) aqueous solutions over Fe(0) nanoparticles were also fit carefully by the modified Langmuir and Freundlich isotherms, respectively.
The Cr-adsorbed Fe(0) nanoparticles measured by FE-SEM and XRD were abnormally incompact, it was possible that Fe(0) nanoparticles were, to some extent, oxidized in the adsorption process. The existence of Cr species on the Fe(0) nanoparticles was also confirmed by XANES. It was found that mainly Cr(III) with a small amount of Cr(0) was adsorbed on the Fe(0) nanoparticles. This work exemplifies the utilization of XANES, XRD, and XPS to reveal the speciation and possible reaction pathway in a very complex adsorption and redox reaction process. EXAFS spectra showed Cr(VI) and Cr(III) all reduce to Cr2O3 while oxidizing the Fe(0) to Fe2O3 electrochemically. It is also very clear that decontamination of Cr species in groundwater via the in-situ remediation with nanophase Fe(0) permeable reactive barriers would be environmentally attractive in the future.

並列關鍵字

Zero-valent iron nanoparticles ； Cr contamination ； borohydride reduction reaction ； adsorption kinetics ； surface analysis ； XANES ； EXAFS

參考文獻

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