using nanoscale zero-valent iron for the remediation of polycyclic aromatic hydrocarbons...

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Using Nanoscale Zero-Valent Iron for theRemediation of Polycyclic Aromatic HydrocarbonsContaminated SoilMing-Chin Chang a , Hung-Yee Shu a , Wen-Pin Hsieh b & Min-Chao Wang ca Department of Environmental Engineering, Hungkuang University, Taichung, Taiwan,Republic of Chinab Department of Soil and Environmental Science, National Chung-Hsin University,Taichung, Taiwan, Republic of Chinac Department and Graduate Institute of Environmental Engineering and Management,Chaoyang University of Technology, Taichung, Taiwan, Republic of ChinaPublished online: 01 Mar 2012.

To cite this article: Ming-Chin Chang , Hung-Yee Shu , Wen-Pin Hsieh & Min-Chao Wang (2005): Using Nanoscale Zero-Valent Iron for the Remediation of Polycyclic Aromatic Hydrocarbons Contaminated Soil, Journal of the Air & WasteManagement Association, 55:8, 1200-1207

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Using Nanoscale Zero-Valent Iron for the Remediation ofPolycyclic Aromatic Hydrocarbons Contaminated Soil

Ming-Chin Chang and Hung-Yee ShuDepartment of Environmental Engineering, Hungkuang University, Taichung, Taiwan, Republic of China

Wen-Pin HsiehDepartment of Soil and Environmental Science, National Chung-Hsin University, Taichung, Taiwan,Republic of China

Min-Chao WangDepartment and Graduate Institute of Environmental Engineering and Management,Chaoyang University of Technology, Taichung, Taiwan, Republic of China

ABSTRACTThe sites contaminated with recalcitrant organic com-pounds, such as polycyclic aromatic hydrocarbons(PAHs) with multiple benzene rings, are colossal andubiquitous environmental problems. They are rela-tively nonbiodegradable and mutagenic, and 16 ofthem are listed in the U.S. Environment ProtectionAgency priority pollutants. Thus, the efficient andemerging remediation technologies for removal ofPAHs in contaminated sites have to be uncovered ur-gently. In this decade, the zero-valent iron (ZVI) parti-cles have been used successfully in the laboratory, pilot,and field, such as degradation of chlorinated hydrocar-bons and remediation of the other pollutants. Never-theless, as far as we know, little research has investi-gated for soil remediation; this study used nanoscaleZVI particles to remove pyrene in the soil. The experi-mental variables were determined, including reactiontime, iron particle size, and dosage. From the results,

both the micro- and nanoscales of ZVI were capable ofremoving the target compound in soil, but the higherremoval efficiencies were by nanoscale ZVI because ofthe massive specific surface area. The optimal operatingconditions to attain the best removal efficiency ofpyrene were obtained while adding nanoscale ZVI 0.1g/g soil within 60 min and 150 rpm of mixing. Thus,nanoscale ZVI has proved to be a promising remedy forPAH-contaminated soil in this study, as well as an op-timistically predictable application for additional pilotand field studies.

INTRODUCTIONThe contamination of surface and subsurface soils withbiorefractory organic chemicals, such as polycyclic aro-matic hydrocarbons (PAHs), is a serious environmentalproblem. PAHs, which are a group of aromatic com-pounds containing two or more benzene rings, are rela-tively ubiquitous and stable and are found in the heavierfractions of petroleum. There are 16 PAHs listed by theU.S. Environmental Protection Agency (EPA) as prioritypollutants because of their toxic and mutagenic nature.Benzo[a]pyrene is one of the most famous known carcin-ogens. The water solubilities of PAHs were found to befairly low.1–4 Some of the PAHs are used for dyestuff,explosives, synthesis of drugs, and biochemical research.The source of PAHs in soil can originate from atmosphericdeposition, oil spills, and incomplete combustion of or-ganic matter. From industrial sites, the source may comefrom under- or above-ground storage tanks with spillsand/or leaks and the conveyance, processing, use, anddisposal of these fuel/oil products. In addition, manyformer manufactured gas plants had soil and groundwater

IMPLICATIONThe sites contaminated with recalcitrant, ubiquitous, toxic,mutagenic, and hardly biodegradable PAHs are colossalenvironmental problems. Thus, the efficient and emergingremediation technology for removing PAHs from the con-taminated sites was used in this study by using the mi-croscale and nanoscale of ZVI powders. From the results,the utilized ZVI in the experiment was capable of removingthe target compound in soil efficiently. Additionally, thehigher removal efficiencies of nanoscale ZVI than mi-croscale ZVI were observed. The study and experimentalconditions have proven that it is highly feasible for soilremediation of PAH contaminations.

TECHNICAL PAPER ISSN 1047-3289 J. Air & Waste Manage. Assoc. 55:1200–1207

Copyright 2005 Air & Waste Management Association

1200 Journal of the Air & Waste Management Association Volume 55 August 2005

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contamination problems because of the prior process op-erations and management practices.5 Thus, the contami-nated sites with PAHs require emerging remediationtechnology urgently. Indeed, some techniques demon-strated the efficient decontamination of PAHs, includingchemical and biological remediation such as Fenton reac-tion for removal of pyrene.6 The surfactants were alsoused in the surface and subsurface soil and groundwaterfor the applications of the solubility enhancement studiesof the hydrophobic compounds. The ability of aqueoussurfactant solutions to recover tetrachloroethylene en-trapped in Ottawa sand was evaluated in four columnexperiments.7 The authors have investigated the effects ofsome surfactants for the successful extraction of phenan-threne in soil.8 On the other hand, the review of biore-mediation of soil contaminated with PAHs was summa-rized by Wilson and Jones,9 who found that in situremediation techniques were considered ineffective forthe removal of most PAHs from contaminated sites. Inthis decade, using zero-valent iron (ZVI) to manipulatehazardous substances in aqueous solutions has also beendemonstrated by some investigators. The batch experi-ments10 used granular ZVI to remove Uranium (VI) at 0.25and 9.3 mg/L within several hours with pH ranges be-tween 2 and 9. The results showed that Uranium-contam-inated waters can be removed by ZVI. Meanwhile, thetrichloroethylene (TCE) and atrazine were feasibly reduc-tive dechlorinated by ZVI.11–12 The long-term perfor-mance of ZVI, packed in columns, for reductive dechlori-nation of TCE was also investigated successfully during a2-year period.13 The persistent organic compound, suchas polychlorinated dibenzo-p-dioxin, in contaminatedsoil was reductive dechlorinated by ZVI, which was capa-ble of stepwise degrading polychlorinated dibenzo-p-di-oxin into octachlorinated dibenzo-p-dioxin, enhancedthe solubility by 4–6 orders over its solubility at ambientconditions.14 Accelerated remediation of pesticide-con-taminated soil was found while adding 5% (wt/wt) of ZVI,which resulted in �60% destruction efficiency of the fivepesticides within 90 days.15 A similar observation wasfound by researchers remediating the herbicide-contami-nated water with ZVI: mixing an aqueous solution of 100�M 3,6-dichloro-2-methoxybenzoicacid with 1.5% of ZVI(wt/vol) resulted into 80% loss of 3,6-dichloro-2-me-thoxybenzoicacid within 12 hr.16 Additionally, the ZVIwas used to deal with the nitrate reduction to ammoniaand reductive degradation of nitrobenzene efficiently.The nearly complete reduction of nitrate to ammoniaoccurs at room temperature and with pressure by ZVI inacidic condition.17 A 50-mL solution of 12.5 mM nitratewas rapidly reduced to ammonia by adding 4 g of 325mesh iron at pH 5. The reduction of nitrobenzene by ZVIwas affected by pH and its concentration so that the

optimum pH was observed to be 3, whereas the majorreductive product was found to be aniline by followingthe zero-order kinetics at various pH values.18 In spite ofthe zero-valent iron, some of the other zero-valent metals,such as zinc (Zn0) or bimetals such as iron/nickel, zinc/nickel, and zinc/palladium (i.e., Fe0/Ni0, Zn0/Ni0, andZn0/Pd0), were investigated for improving in situ environ-mental remediation of TCE in water rather than singlemetal.19–20 The investigators found that degradation ofTCE in groundwater by Zn0 was nearly 10 times higherthan that of Fe0. Whereas Fe0 or Zn0 associated with theother metals, such as Ni and Pd, both of the reductionefficiencies of TCE strongly improved. The TCE reductionrates of Zn0/Ni0and Zn0/Pd0 were the most rapid, yet Fe0

diminishing surface activity was reactive again by theaddition of Pd0 or Ni0, which played the role as a catalyst.Besides, the dechlorination of chlorophenols21 by Fe0/Pd0

powder by catalytic reduction was effective and followeda pseudo–first-order reaction. While adding 0.048% Pd/Fe, the rate constants were 0.0215, 0.0155, and 0.0112min�1 for o-, m-, and p-chlorophenol, respectively.

Even with the above observation of efficient reduc-tions of organic compounds by the ZVI, an additional stepof investigation on the nanoscale ZVI as a catalyst haserupted in nanotechnology application in environmentalremediation.22 More and more researches are focusing onthe innovative nanoscale ZVI to remedy persistent or-ganic pollutants in contaminated sites. For examples, TCEand polychlorinated biphenyls23 were degraded signifi-cantly and promptly by the synthesized nanoscale ZVIand palladized iron (Pd/Fe) particles because of the char-acteristics of high surface area-to-volume ratios and highreactivity. The specific surface area of the synthesizedmetal particles, 33.5 m2/g, was tens of times greater thanthat of the commercially available ZVI powder (�10 �m),0.9 m2/g. Moreover, the surface–area-normalized reactiv-ity constants were �100 times higher than that of com-mercial microscale ZVI powder.24 Besides, a field demon-stration was performed by the nanoscale bimetallicparticles,25 which were fed into groundwater contami-nated with TCE and other chlorinated aliphatic hydrocar-bons at a manufacturing site. There was �1.7 kg ofnanoscale ZVI that was fed into the test area over a 2-dayperiod to make TCE reduction efficiencies up to 96%within 4-week monitoring time. Recently, Zhang26 de-scribed nanoscale ZVI particles for environmental reme-diation and addressed that nanoscale ZVI particles pro-vide a new generation of environmental in situ cleanuptechnology both in laboratory and pilot applications. As aremedy it is more efficient, cost effective, and time savingfor the pollutants, such as chlorinated organic solvents,organochlorine pesticides, and polychlorinated biphe-nyls. On the other hand, the rapid reductive destruction

Chang, Shu, Hsieh, and Wang

Volume 55 August 2005 Journal of the Air & Waste Management Association 1201

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of hazardous organic compounds, such as chlorinatedorganic compounds and nitroaromatic compounds, inthe aqueous phase by nanoscale ZVI in anaerobic batchsystem was efficient.27 The nanoscale ZVI rapidly trans-formed TCE, chloroform, nitrobenzene, nitrotoluene, di-nitrobenzene, and dinitrotoulene under ambient condi-tions, which resulted in complete disappearance of theparent compounds from the aqueous phase within a fewminutes.

The purpose of this work was to conduct the feasi-bility study of remediation of pyrene-contaminated soilby using the nanoscale ZVI particles. The experimentalparameters, such as time, ZVI particle diameters, anddosage, were identified in the operating process. Thus,the experimental results obtained from the batch sys-tem may be expected optimistically to provide addi-tional possibility of application for pilot or full-scalesite remediation operations.

EXPERIMENTAL METHODSMaterials

Pyrene (C16H10, 97% purity) with molecular weight 202,mp 156 °C, bp 404 °C, vapor pressure 4.5 � 10�6 mmHg,water dissolution 0.14 mg/L, and log Kow 5.32, was pur-chased from Aldrich. Hexane and acetone were obtainedfrom Merck. Sodium sulfate anhydrate (Na2SO4) was pur-chased from Mallinckrodt. Iron fine powder (45–60 �m,99%), sodium borohydride (BH4Na, 95%) and iron chlo-ride (FeCl3 � 6 H2O, 99%) were purchased from Riedel-se-Haen. The double-deionized water (�18 M�cm) used inall of the aqueous solutions and dilutions was purifiedusing a Milli-Q deionizing system. Washed silica sand(0.45–0.55 mm) for nanoscale ZVI recovery test was ob-tained from Ushen Co. A Tapumei series (Tf) red soil wassampled from Mingen village, Nai-tuo county in centralTaiwan. The soil characteristic was analyzed and listed asTable 1. It was classified as clay loam.

Nanoscale ZVI was chemically synthesized by slowlyadding 1.6 M of sodium borohydride (NaBH4) solution

into the 1 M of iron chloride (FeCl3 � 6 H2O) solution withmagnetic stirring to make ferric iron (Fe3�), which wasreduced and transformed into ZVI precipitation ofnanoscale at ambient temperature23 as the equation be-low.

FeH2O63 � 3BH 4

� � 3H2O 3 Fe0 2

� 3BOH3 � 10.5H2 (1)

After, the nanoscale ZVI particles were dried andstored in a desiccator, which was filled by nitrogen gas toprevent additional oxidation. Morphology of thenanoscale ZVI particle was observed by a JEOL 6330CFField Emission Scanning Electron Microscope to charac-terize and identify the size in the range of nanoscale(�100 nm) as shown in Figure 1a. Meanwhile, the distri-bution of particle size was detected to be mainly locatedin the range of 50–80 nm by a Brookhaven InstrumentsCorp-90 plus, Particle Size Analyzer with Particle SizingSoftware as shown in Figure 1b. BET surface area obtainedby the Quantachrome Autosorb Automated Gas SorptionSystem for the synthesized nanoscale ZVI and commercialmicroscale iron particle were 140.8 and 1.82 m2/g, respec-tively. Thus, the surface area of nanoscale ZVI was �77times greater than that of the micro-iron particle.

ProcedureThe target compound was spiked with the soil that con-tains no pyrene to simulate the contaminated soil. Thepyrene was dissolved in acetone thoroughly by adding 10ml of a 20 pyrene mg/L acetone solution into the 40-mLamber glass vials with screw caps containing 2 g of Ta-pumei red soil made by well mixing in 150 min, so thatthe obtained concentration was 100 mg of pyrene forevery kg soil. After the spiked samples were left in a fumehood for 24 hr to allow acetone evaporating, target com-pound remained and was distributed homogeneously insoil.

The experiment was conducted in a 40-mL borosili-cate glass vial containing 2 g of soil (100 mg pyrene/kgsoil). Both of the micro- and nanosizes of ZVI were addedinto spiked soil samples by supplemental 4-mL Milli-Qdeionized water for every sample while mixing in 150rpm. The experimental variables were reaction time, thediameter of ZVI particles, and dosage of ZVI. The water su-pernatant was decanted after reaction, after the additionof 2 g of anhydrous sodium sulfate into every soil sample,with thorough mixing for moisture prevention. Thepyrene concentrations of soil samples were then extractedby sonication method with n-hexane addition to bringthe final volume to 10 mL using Sonicator Misonix XL-2020, which is followed by EPA method 3550B with a

Table 1. The characteristic of red soil in Tapumei series of central

Taiwan.

Characteristic Value

Silt, % 42

Clay, % 36

Sand, % 22

Texture CL

pH 4.8

Organic matter, % 2.19

CEC, cmol/kg 10.9

Organic carbon, g/kg 2.7

Notes: CL � clay loam; CEC �cation exchange capacity.



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horn-type device equipped with a tita-nium tip (ultrasonic disrupter, power of300 W) and pulsing capacity.28 The pro-cess was disrupted for 3 min while thehorn tip was positioned just below thesurface of the solvent yet above the soilsample. Finally, the extract of pyrene so-lution was filtered through a 0.2-�m fil-ter, then 10 �L was injected into high-performance liquid chromatography,while using a Waters 600 equipped withan UV detector (� � 254 nm) and a col-umn of Supelco Sil TM LC 18 (15 cm �

4.6 mm, with 5 �m silica). Chromato-graphic conditions were mobile phaseisocratic of 80% acetonitrile and 20%deionized water, flow rate of 1 mL/min,operation pressure from 926 to 1073 psi,and retention time of 6.5 min. All of thesamples were conducted in triplicate,and the blank samples were carried outusing deionized water without ZVI addi-tion.

RESULTS AND DISCUSSIONEffects of Reaction Time

Figure 2 shows the effect of pyrene re-moval versus catalytic reaction timewhile adding microscale and nanoscaleof ZVI particles (Fe0). The complete reac-tion time of 300 min is expressed in Fig-ure 2a, whereas the partially enlargedtime period from 0 to 60 min in Figure2b has a clear sight of the early and mostidentical reaction stage. The figureshows the fast changes of pyrene con-centration with reaction time up to 50% removal at theinitial stage within 30 min, while following the exponen-tial decline until 300 min. Thus, this scenario implies thatthe catalytic reaction takes place initially within the early30 min. After this period of time, the following pyreneremoval nearly changes. However, by consideration ofboth the reaction completion and operation cost savings,the reaction time was chosen as 60 min for the rest ofexperiments.

Kinetics of Concentration Removal by TimeTo avoid the effect of ZVI concentration change by cor-rosion on the kinetics during the reactions, we addedstoichiometric excess amounts of ZVI particles comparedwith that of pyrene applied. The observation implies thatpyrene removal under this condition complies with thefirst-order reaction with respect to pyrene concentration.

Although no consideration of the ZVI concentration ef-fect, the reaction can be described as a pseudo-first-orderreaction with respect to pyrene concentration as given ineq 2.

�dCP

dt� k�CP (2)

where k is the observed rate constant of first-order reac-tion and Cp expresses the concentration of pyrene. Therate constants can be obtained by regression of plotting anatural log of pyrene concentration with respect to reac-tion time according to eq 3.

ln�CP

CP0� � �k � t (3)

Figure 1. (a) Morphology of nanoscale ZVI by a JEOL 6330CF field emission scanningelectron microscope. (b) Particle size distribution chart by a Brookhaven Instruments Corp.�90 plus particle size analyzer.



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where Cp0 is the initial concentration of pyrene. The re-moval efficiency can be expressed as the following equation:

Removal Efficiency � 1 �CP

CP0� 1 � e�kt (4)

Because the reaction occurs in soil-water-iron inter-phase, the removal efficiency is limited by phase transfermechanism and hardly reaches 100% removal. Thus, theremoval efficiency is modified by the ultimate removalefficiency factor ( ) as follows (eq 5). Therefore, the cal-culated results of regression for rate constants and theultimate removal efficiency factors ( ) are presented inTable 2.

Modified Removal Efficiency � 1 � e-kt (5)

Effect of Particle SizeAlthough the pyrene removal by ZVI involves reaction atthe metal surface, the quantity of metal surface area,which is also the most significant experimental variables,strongly influences the kinetics of pyrene removal andaffects reduction rates. The pretreatment by acid such ashydrochloride acid (HCl) before the usage of nanoscaleiron is especially necessary and important for keeping asmany active sites of iron surface area as possible shown in

Figure 3, which shows almost twice the removal efficien-cies of prior acid wash (30%) than without pretreatment(15%). Besides, the pyrene removal efficiency as a func-tion of time by adding various particle sizes of iron con-tains microscale and synthesized nanoscale ZVI. The re-action was performed under 150 rpm of mixing speed andwith iron dosage of 100 mg/g soil to react with soil sampleshown in Figure 4. The BET surface area of synthesizednanoscale iron was massive and much larger than that ofmicroscale iron, so that the pyrene removal efficiency bynanoscale iron was better. With a reaction time of 30 min,the removal efficiency of pyrene reached �70% bynanoscale iron and 14% by microscale iron, respectively.

Effect of Iron DosageThe effect of iron dosage is one of the major variables thataffects the removal efficiencies as shown in Figure 5a.Increasing the initial dosage of iron particles speeds upsubstantially the initial reaction, whereby pyrene collides

Figure 2. Pyrene removal efficiency vs. time for nanoscale andmicroscale Fe0 while at 0.05 g Fe0/g soil dosage and 150 rpm mixingspeed (a) for reaction time up to 300 min and (b) with nonlinearregression of rate expression for 60 min of reaction time.

Table 2. Model regression parameters for the pyrene removal by zero-

valent nanoscale iron in soil.

Dosage,g Fe0/g soil �, % k, min�1 R2

Nm-Fe0 without pretreatment 0.0125 19.60 0.205 0.932

0.05 34.86 0.237 0.999

0.15 40.79 0.261 0.971

Nm-Fe0 with pretreatment 0.0125 21.80 0.202 0.909

0.05 55.20 0.263 0.978

0.15 77.03 0.381 0.997

Figure 3. Pyrene removal efficiency vs. time for nanoscale Fe0 withor without acid pretreatment. The iron dosage was 0.0125 g/g soil,and mixing speed was 150 rpm.



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with the more surface-active sites of iron particles. Thefigure shows pyrene removal efficiency as a function oftime by various nanoscale iron doses from 0.00625 g to0.1 g/g soil with a mixing speed of 150 rpm. From exper-imental data, the removal efficiencies by iron dosage of0.1, 0.025, and 0.00625 g per 1 g soil reached 72, 30, and18%, respectively, at 60 min of reaction time. Besides, thecontrol soil samples without the addition of iron wereused to compare with the samples adding iron shown inFigure 5a, which shows insignificant reduction of pyrene.That implies that pyrene cannot be removed with no ironaddition in the controlled soil samples. Moreover, theremoval efficiencies of pyrene as function of nanoscaleiron dosages are shown in Figure 5b, which is dependenton nanoscale iron dosage. Meanwhile, the relationship offirst-order reaction was developed because the reactivenanoscale iron site increases proportionally with thenanoscale iron dosage. The reaction rate linearly in-creased with incrementing amounts of iron up to a dosageof 0.05 g/g soil under this experimental condition.

Effect of Multistage ReactionThe reaction by adding iron step by step in multistage wasperformed to increase the removal efficiency as shown inFigure 6. For example, the first stage of adding 0.025 g/gsoil of nanoscale iron in the soil samples can achieve�23% of removal efficiency in 30 min. During a secondstage, another 0.025 g/g soil of nanoscale iron was againadded into the same residual soil samples, which incre-ments the removal efficiency as well. Furthermore, thetotal removal efficiency of the three-stage reactions wasadded up to 65%, which is also about three times that of

single-stage reaction. Similar result of a three-stage andsingle-stage by nanoscale iron addition of 0.00625 g/g soilreaches removal efficiency of 23% and only �10%, re-spectively. Meanwhile, it is very interesting to observethat removal efficiency of a single reaction stage of 0.025g iron/g soil was 23%, which was nearly the same of thesum of three-stage reaction of 0.00625 g/g soil addition(0.01375 g iron/g soil). The differences came to 0.01125 giron/g soil while reaching almost the same efficiency. Thisimplies that reaction with multistage of a small amount ofaddition has clearly increased reaction efficiency than onetime of a greater pulse amount addition of iron particles.

Feasibility and Cost AnalysisTechnology by injecting the nanoscale ZVI particles withwater into the subsurface of contaminated site was dem-onstrated successfully for reduction of contaminant infield groundwater.25,26 For soil application, the nanoscaleparticles need to be injected into subsurface soil and toflow liberally through the area of contaminated soil toperform an excellent mixing of iron and soil particles. Thenanoscale ZVI particles applied on soil remediation are

Figure 5. (a) Removal efficiency of pyrene as a function of time.The nanoscale Fe0 dosages were 0.0625, 0.025, and 0.1 g/g soil. (b)Pyrene removal efficiency for 60 min of reaction time vs. nanoscaleFe0 dosage.

Figure 4. Comparison of pyrene removal efficiency by nanoscaleFe0 with microscale Fe0. The iron dosage was 0.1 g/g soil, andmixing speed was 150 rpm.



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similar to in situ chemical remediation, such as Fenton

oxidation and soil washing. Thus, the operation cost was

compared such that soil washing29 was $151/metric ton

($137/t) in a pilot scale site by surfactant addition. The

soil contained PAH of 550–1,700 ppm and pentachloro-

phenol of 48–210 ppm in Escambia Wood Treating Com-

pany Superfund Site, Pensecola, FL. Remaining soil vol-

ume contained 45 ppm of PAHs and 3 ppm of

pentachloro-phenol. Another case, such as the 32-hectare

site with full-scale integrated treatment both for PAH and

metal recovery by soil washing, cost $100/t in Ataratiri

Site, Toronto, Ontario, Canada. In addition to the cost of

operation, the cost of nanoscale iron particle is also a

considerable expense. The cost of commercially available

nanoscale ZVI particles was pretty high once in the mar-

ket, although it becomes less than $50/kg in mid-2004.29

Meanwhile, it is expected to be additionally reduced for

the more mature technique and increasing demand and

supply. Although the cost is still high now, the per-surface

area cost was competitive to the regular zero valent iron

particles. According to the larger surface area, the per-

surface area cost was less than $0.0033/m2, which was

in comparison with $0.33/m2 for iron filings of 0.5-mm

diameter. Therefore, a smaller dosage of nanoscale iron

particles was needed for reduction of soil contaminant so

as to reduce the operation cost. Base on the above results,

we propose that soil remediation by nanoscale ZVI parti-

cles is a highly potential technology for future environ-

mental applications.

CONCLUSIONSThis study has shown that reductive catalysis of pyrene insoil samples can be achieved in 60 min by contacting thesoil with nanoscale ZVI powders in aqueous solution un-der ambient conditions with no pH control. Approxi-mately 70% of pyrene in soil samples was reductivelydegraded in 60 min with little intermediates. In our batchtest, the kinetics of pyrene reduction was dominated byiron dosage, as well as particle size and BET surface area ofiron particles. The kinetics of pyrene reduction can bedescribed as a pseudo–first-order reaction with respect tothe pyrene concentration in the presence of stoichiomet-ric excess of iron particles, and the observed reaction rateconstant (k) was 0.103–0.381 min�1 for synthesizednanoscale ZVI at dosage of 0.00625 to 0.15 g/g soil. Re-moval efficiency linearly increases with increasing irondosage up to 0.05 g/g soil. Besides, multistage addition ofiron particles leads to higher removal percentage in com-parison with single addition of iron particles. Thus, formultistage addition, it may be a suitable operating condi-tion. With low per-surface area cost of less than $0.0033/m2, the soil remediation technology uses nanoscale ZVIparticles has high potential to be one of the feasible re-mediation technologies for field applications. Meanwhile,the future goal of this research for in situ application is topour nanoscale ZVI into the subsurface soil of a contam-inated site instead of digging it out.

ACKNOWLEDGMENTSThe authors appreciate the research funding granted bythe Taiwan National Science Foundation (NSC 92–2211-E-241-009).

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Figure 6. Removal efficiency of pyrene in soil for multistage of Fe0

addition procedure. The nanoscale Fe0 dosages were 0.0625 and0.025, respectively. Each additional stage performed was 30 min ofreaction time.



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About the AuthorsMing-Chin Chang is an assistant professor in the Depart-ment of Environmental Engineering, Hungkuang University.Hung-Yee Shu is an associate professor in the Departmentof Environmental Engineering, Hungkuang University. Wen-Pin Hsieh was a master’s student in the Department of Soiland Environmental Science in National Chung-Hsin Univer-sity during the time of this study. Min-Chao Wang is aprofessor in the Department and Graduate Institute of En-vironmental Engineering and Management, Chaoyang Uni-versity of Technology. Address correspondence to: Ming-Chin Chang, Department of Environmental Engineering,Hungkuang University, 34 Chung-Chie Rd., Shalu,Taichung county, Taiwan 433, Republic of China; phone:�886-4-2631-8652 x4113; fax: �886-4-2652-5245; e-mail:[email protected].



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using nanoscale zero-valent iron for the remediation of polycyclic aromatic hydrocarbons...

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