cyclodextrin-enhanced extraction and removal of 2,4-dinitrotoluene from contaminated soils

ENVIRONMENTAL ENGINEERING SCIENCEVolume 25, Number 4, 2008© Mary Ann Liebert, Inc.DOI: 10.1089/ees.2005.0010

Cyclodextrin-Enhanced Extraction and Removal of 2,4-Dinitrotoluene from Contaminated Soils

Amid P. Khodadoust,* Omprasad Narla, and Srividya Chandrasekaran

Department of Civil & Materials EngineeringUniversity of Illinois at Chicago

Chicago, IL 60607

ABSTRACT

The extraction and removal of 2,4-dinitrotoluene (2,4-DNT) from contaminated soils were evaluated using aque-ous solutions of hydroxypropyl-�-cyclodextrin (HPCD). The cyclodextrin-enhanced removal of 2,4-DNT fromsoils was investigated as function of soil type and concentration of HPCD solutions up to 5% HPCD (w/w).Three soils were spiked with 480 mg of 2,4-DNT per kg of soil: kaolin, a low-buffering clayey soil; montmo-rillonite, a soil with high specific surface area; and glacial till, a high-buffering silty soil with organic matter.The glacial till was a field soil containing 2.8% organic matter. The solubility of 2,4-DNT in 5% HPCD solu-tion increased approximately threefold compared to solubility of 2,4-DNT in water. For kaolin, water was aseffective as HPCD solutions. For montmorillonite, the 5% HPCD solution was the most effective extractant.For glacial till, the 2% HPCD solution was as effective an extractant as the 5% HPCD solution. Although thesolubility of 2,4-DNT in 2% HPCD was enhanced approximately 1.7-fold, the extraction of 2,4-DNT fromglacial till and montmorillonite using 2% HPCD was enhanced more than twofold in sequential extractions.Three-stage sequential extractions with 2% HPCD followed by two water rinse stages resulted in the removalof 75 and 64% of 2,4-DNT from the glacial till and montmorillonite soils, respectively, whereas five-stage se-quential extractions with water alone removed 33 and 30% of 2,4-DNT from glacial till and montmorillonite,respectively. The sequential extraction results showed that the 2% HPCD solution was an effective extractantfor remediation of soils with strong retention of 2,4-DNT.

Key words: dinitrotoluene; extraction; soil; remediation; cyclodextrin

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*Corresponding author: Department of Civil & Materials Engineering, University of Illinois at Chicago, Chicago, IL 60607. Phone:312-996-3435; Fax: 312-996-2426; E-mail: [email protected]

INTRODUCTION

CONTAMINATION OF SOIL and groundwater by munitionswastes and energetic compounds are of environmental

concern due to the toxicity exhibited by compounds such as2,4-dinitrotoluene (2,4-DNT) (Griest et al., 1993; Simini etal., 1995). Surface and subsurface soils have been contam-

inated with releases from munitions manufacturing facilities(e.g., munitions wastewaters), spills, and military field op-erations (Pennington and Patrick, 1990; Haderlein et al.,1996; Hundal et al., 1997; Sheramata et al., 1999). Con-taminants released from contaminated soils find their wayinto groundwater, thus polluting a potential source of drink-ing water. Methanol, acetone, and acetonitrile have been

used in extraction and flushing of TNT from soils (Selim etal., 1995; Sunahar et al., 1998). Water alone has been shownto be somewhat effective in soil washing of 2,4-DNT andTNT (Li et al., 1997; Zhang et al., 2001). Effective reme-diation technologies are needed to clean up soils contami-nated with nitroaromatic explosives and munitions wastes(Rodgers and Bunce, 2001) without the addition of chemi-cal agents that increase the environmental impact of the con-taminated soil and water

Cyclodextrins are nonhazardous and environmentally ac-ceptable organic substances that may biodegrade in soil andwater after their introduction into an environmental system.Cyclodextrins are organic molecules consisting of linkedglucose units. Cyclodextrins possess high aqueous solubili-ties due to the hydroxyl functional groups on their exterior,while having a hydrophobic organic cavity in the interiorwhich allows for inclusion complexation between a nonpo-lar organic molecule and the cyclodextrin molecule. Aque-ous solutions of cyclodextrin are capable of dissolving organic compounds with low aqueous solubility at concen-trations above their solubility limits. In addition to 1:1 in-clusion complexes, �-cyclodextrins can make 2:1 inclusionswith larger organic molecules (Wang and Brusseau, 1993;Brusseau et al., 1997), and �-cyclodextrins can be used forsolubilization of even larger organic molecules (Blyshak etal., 1988).

Greater solubilization of organic compounds enhances thedesorption and extraction of organic compounds from soils.Hydroxypropyl-�-cyclodextrin (HPCD) has been used forthe solubilization and desorption of phenanthrene from soils(Badr et al., 2004; Ko and Yoo, 2003; Reid et al., 2000),enhanced biodegradation of phenanthrene from contami-nated soils (Brusseau et al., 1997), for assessing the bioavail-ability of several polycyclic aromatic hydrocarbon com-pounds in sediments (Reid et al., 2000; Cuypers et al., 2002),for in situ flushing of hydrophobic organic compounds (McCray and Brusseau, 1998), for solubilization of pen-tachlorophenol in water (Hanna et al., 2004), and for re-moval of chlorinated solvents from porous media (Bovinget al., 1999). Cyclodextrin solutions have been used for des-orption and extraction of energetic compounds TNT and

RDX from soils (Hawari et al., 1996; Sheramata and Hawari,2000).

The complexation of 2,4-DNT with HPCD would enhancethe solubility of 2,4-DNT in HPCD solutions through thelikely formation of a 1:1 inlcusion complex between 2,4-DNT and the hydroxypropyl-�-cyclodextrin (HPCD) mole-cules, resulting in the enhanced desorption and extraction of2,4-DNT from soil matrices. This study investigated the cy-clodextrin-enhanced solubilization and extraction of 2,4-DNT from contaminated model soils as function of soil typeand HPCD concentration in solution.

MATERIALS AND METHODS

Chemicals

The 2,4-DNT was selected as a representative munitionswaste compound with a log Kow of 1.98 at 25°C. Neat 2,4-DNT (97% purity) and 1-chloro-3-nitrobenzene (purity98%) were obtained from Aldrich Chemicals (Milwaukee,WI). Reagent grade acetone, acetonitrile, and hexane wereobtained from Fisher Scientific (Fairlawn, NJ). HPCD, witha purity of 97%, was obtained from Fisher Scientific. Thedeionized (DI) water was high purity water with a resistancegreater than 18 M�.

Soils

The soils selected for this study were montmorillonite,glacial till, and kaolin. Table 1 shows some physical andchemical properties of these soils. Soil particle sizes wereobtained from dry sieving determinations. Montmorilloniteand kaolin are model natural soils containing mainly smec-tite and kaolinite clay minerals, respectively. Montmoril-lonite is a soil with high porosity and large specific surfacearea. Neither montmorillonite nor kaolin contains soil or-ganic matter. Montmorillonite and kaolin were obtainedfrom Aldrich Chemicals and Fisher Scientific, respectively.The glacial till was a native soil with natural soil organicmatter content of 2.8% obtained from a field site in theChicago area. The soil properties shown in Table 1 show

KHODADOUST ET AL.616

Table 1. Soil properties.

Soil Montmorillonite Kaolin Glacial till

Sand (%) 19 04 16Silt (%) 50 18 47Clay (%) 31 78 37USDA textural class Silty clay loam Clay Silty clay loamBET surface area (m2/g) 220–270 1–50 N/AOrganic matter (%) �0.1 �0.1 2.8pH �3.5 �4.9 7.7Cation exchange capaciy (mEq/100 g) 022.6 �1.3 13

that the particle size distributions of montmorillonite andglacial till are similar. The pH values of the montmorilloniteand kaolin soils were acidic, while the pH value of the glacialtill soil was slightly alkaline.

The soils were spiked with 2,4-DNT inside the labora-tory. The solid 2,4-DNT was dissolved in hexane to preparestock solution of 2,4-DNT in hexane. The stock solution of2,4-DNT in hexane and 1 liter of hexane were added to 500g soils in glass beakers. The soil–hexane–2,4-DNT slurrywas mixed thoroughly using stainless steel spatulas. Afterthe addition of 2,4-DNT to the soil slurry, the spiked soilslurries were placed in an aluminum pan inside a fume hoodto air dry over a period of 7 to 10 days. After drying thespiked soils, the spiked soils were extracted with 1:1 (v/v)mixture of acetone–acetonitrile for 24 h to determine the ini-tial concentration of 2,4-DNT in spiked soils after volatiliza-tion of hexane.

Analysis of 2,4-DNT

The concentration of 2,4-DNT in soil extracts was deter-mined using gas chromatography (GC) according to U.S.EPA Method 8091 (1996). The liquid soil extracts were di-luted in 10 mL ethanol using various dilution ratios. Etha-nol was used for dilution of samples because the GC stan-dards were prepared in ethanol. Then 5 mL of DI water wereadded to the 5 mL of diluted ethanol samples, and 3–5 dropsof 10 N sodium hydroxide were added to 10 mL of wa-ter–ethanol dilutions. The 2,4-DNT was extracted from theaqueous water–ethanol phase into an hexane phase for GCanalysis. For GC analysis, 1-chloro-3-nitrobenzene was usedas surrogate standard. The hexane extracts were injected intoan Agilent 6890 Series GC (Wilmington, DE) equipped witha microelectron capture detector (�ECD) for analysis of 2,4-DNT. A DB-5 (J&W, Folsom, CA) capillary GC columnwas used with helium and argon–methane as carrier andmake-up gases, respectively. The GC was calibrated for 2,4-DNT analysis regularly using a five-point standard calibra-tion curve with freshly prepared standards, and the standardcalibration was checked for consistency with check stan-dards routinely.

2,4-DNT solubility

The experiments for determining the solubility of 2,4-DNT in cyclodextrin solutions were carried out in triplicate.Based on the reference data for solubility of 2,4-DNT in wa-ter, amounts of solid 2,4-DNT several times greater than thesolubility limit were added to aqueous cyclodextrin solu-tions. The mixtures of 2,4-DNT and the solution were mixedin glass serum bottles on a tumbler at 18 rpm and 24°C. Af-ter 7 days of mixing, the remaining solid 2,4-DNT particleswere separated from solution by centrifugation at 6,500 �g for 20 min. The liquid filtrates were analyzed for 2,4-DNTusing GC.

Single-stage batch extractions

Batch extractions were carried out in Teflon centrifugetubes and glass serum bottles. Soil and solution were addedto the bottles using soil:solution extraction ratios of 1:5, 1:10and 1:20 g/mL. The bottles were capped and placed insidea rotating tumbler and shaken for 24 h at 18 rpm. Batch ex-tractions were performed in triplicate. After shaking, the bot-tles were removed from the tumbler, the liquid was sepa-rated from the soil using centrifugation at 6,500 � g for 20min. The liquid extracts were analyzed for 2,4-DNT usingGC. Preliminary GC analysis showed that there was no dif-ference between 2,4-DNT concentrations in the liquid phaseafter either centrifugation or filtration of soil–liquid slurryfor all soils.

Multistage sequential extractions

Sequential extractions were carried out in a fashion sim-ilar to single batch extractions. After each single batch ex-traction period, the soil–solution slurry was centrifuged toseparate the soil and the spent solution. The spent solutionfrom the first stage extraction was analyzed for 2,4-DNT.After centrifugation, the once-extracted soil was subse-quently exposed to fresh extracting solution for anotherbatch extraction stage. After the second batch extractionstage, the soil–solution mixture was centrifuged to separatethe soil and spent solution. The twice-extracted soil was fur-ther extracted in subsequent stages until the last extractionstage.

RESULTS AND DISCUSSION

Cyclodextrin-enhanced solubilization

The solubility of 2,4-DNT in HPCD solutions was deter-mined. The enhancement in the apparent solubility of a neu-tral organic compound complexed with HPCD (Wang andBrusseau, 1993) can be written as

S/S0 � 1 � �fc

where the (S/S0), S, S0, fc, and � are the relative solubility,the apparent or enhanced solubility, aqueous solubility, thefraction of HPCD in solution (w/w or w/v), and the solu-bility enhancement factor, respectively. The relative solu-bility of 2,4-DNT is shown as a function of the HPCD frac-tion (w/w) in Fig. 1. The data from Fig. 1 show that therelative solubility of 2,4-DNT increased with concentrationof HPCD in solution in linear fashion, indicative of a 1:1inclusion complex between 2,4-DNT and HPCD. The innercavity of HPCD is reported to have a volume of 0.346 nm3

(Wang and Brusseau, 1993). The molecular volume of 2,4-DNT was determined as 0.233 nm3 using the method em-ployed by Wang and Brusseau (1993) based on solute dif-fusion volume of organic molecules using the Fuller’s group

CYCLODEXTRIN-ENHANCED REMOVAL OF 2,4-DINITROTOLUENE FROM SOILS

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contribution method (Lyman et al., 1990). Because the mo-lecular volume of 2,4-DNT is smaller than the size of theHPCD cavity, the 2,4-DNT molecule would be fully con-tained within the HPCD cavity. The relative solubility in-creased from 1 (water) to 2.9 (5% HPCD), indicating an ap-proximately threefold increase in apparent solubility of2,4-DNT in a solution containing 5% HPCD, with a �-valueof 0.407 determined from the plot.

Cyclodextrin-enhanced batch extraction

The montmorillonite, glacial till, and kaolin soils, eachcontaminated with 480 mg 2,4-DNT per kg soil, were ex-tracted with several aqueous HPCD solutions. The maxi-mum concentration of 2,4-DNT in liquid would be 96 mg/Lusing the lowest extraction ratio of 1:5 (g/mL) for completeextraction of the 2,4-DNT from any of the three soils; thismaximum concentration was well below the solubility of2,4-DNT in saturated solutions of the extractants (e.g., withan approximately solubility of 200 mg/L of 2,4-DNT in wa-ter). Therefore, none of the aqueous phase concentrationsafter extraction were close to the saturation capacity of theextracting solutions.

The data for 24-hour extraction of 2,4-DNT from the mont-morillonite, glacial till, and kaolin soils are shown in Fig. 2a–c,respectively. The soil extraction data for montmorillonite pre-sented in Fig. 2a show that more 2,4-DNT was extracted frommontmorillonite with increasing concentration of HPCD in so-lution at all three soil:solution extraction ratios. The data showthat at lower extraction ratios (g/mL) of 1:5 and 1:10, the 5%HPCD solution extracted significantly more 2,4-DNT from

montmorillonite compared to 1 and 2% HPCD solutions. Thedata from Fig. 2b show that at all three soil:solution extrac-tion ratios, the extractions of 2,4-DNT from glacial till weresimilar for the 2 and 5% HPCD solutions. The extraction datapresented in Fig. 2 show that the extraction of 2,4-DNT wasthe greatest from the kaolin soil. The data from Fig. 2c alsoshow that at an extraction ratio of 1:20 (g/mL), water was aseffective as HPCD solutions for extraction of 2,4-DNT fromkaolin.

After performing the batch extraction experiments for 24h, experiments were carried out to determine the extractionkinetics within 24 h for removal of 2,4-DNT using HPCD so-lutions. The extraction data presented in Fig. 2 showed thatthe 2% HPCD solution was effective for extraction of 2,4-DNT from montmorillonite and glacial till, while the 1%HPCD solution was effective for extraction from kaolin. Us-ing a soil:solution extraction ratio of 1:10 (g:mL), extractionkinetics were determined for all three soils. The extraction kinetics for removal of 2,4-DNT from montmoril-lonite, glacial till, and kaolin using 2% HPCD, 2% HPCD,and 1% HPCD solutions are shown in Fig. 3a–c, respectively.The extraction kinetics data in Fig. 3 show that most or all ofthe extractable 2,4-DNT was removed from soil within 1 hof extraction, and that an extraction period of 24 h was suf-ficient to remove the extractable 2,4-DNT from all three soils.

Effect of soil type on cyclodextrin-enhancedextraction of 2,4-DNT

According to Fig. 2c, water was found to be as effectiveas HPCD solutions for extraction of 2,4-DNT from kaolin;


Figure 1. Solubility of 2,4-DNT in HPCD solutions.

therefore, the relative extraction ratios are discussed furtheronly for montmorillonite and glacial till soils. Because therelative solubility (S/S0) of a substrate (organic compound)in a 1:1 inclusion complex with cyclodextrin increases lin-early with fraction of cyclodextrin in solution (fc) with slopefactor of �, the expected enhancement in the extraction ofthat compound from soil due to the cyclodextrin-enhancedsolubilization of the extracted compound may be written as

E/E0 � 1 � ��fc

where E and E0 are the cyclodextrin-enhanced extractionand the extraction with water, respectively, and (E/E0) is therelative extraction. The � is a coefficient related tosoil–solute–solution interactions. An � value of 1.0 denotesthe lack of specific soil–solute–solution interactions asidefrom solute–solution interactions, where enhanced desorp-



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Figure 2. Extraction of 2,4-DNT from soils.

tion of the compound from soil occurs fully according to theenhancement in solubilization of compound in the HPCDsolution (a solute–solution interaction).

The cyclodextrin-enhanced extraction of 2,4-DNT frommontmorillonite is shown in Fig. 4a–c for extraction ratiosof 1:5, 1:10, and 1:20 (g/mL), respectively. The results pre-sented in Fig. 4 show that the relative extraction increasedlinearly with increasing concentration of HPCD in solution,indicating that the cyclodextrin-enhanced desorption of 2,4-DNT from montmorillonite was linear with respect to HPCDconcentration. The linear dependency of extraction onHPCD concentration is shown by a twofold increase in ex-

traction for the 5% HPCD solution, less than the threefoldincrease in solubility for the 5% HPCD solution (Fig. 1).The slope of the plots in Fig. 4a–c was determined to havean average value of 0.192 (�� value), resulting in an aver-age �-value of 0.473 (� � 0.407). The linear increase in ex-traction indicates that as 2,4-DNT desorbs from montmoril-lonite into the HPCD solution, it continues to form a 1:1inclusion with HPCD for all HPCD solutions. The � valueof 0.473 (less than 1.0) indicates that the desorption of 2,4-DNT from the surface of montmorillonite was hindered bysoil–solute–solution interactions such as the strong retentionof 2,4-DNT on the surface of clay and the swelling of the


Figure 3. Extraction of 2,4-DNT from soils as function of time.

montmorillonite due to the expansion of interclay region,and that the expected increase in desorption of 2,4-DNTfrom soil solely due to the solute–solution interaction (en-hanced solubility) between 2,4-DNT and HPCD solutionsdid not occur.

The results presented in Fig. 5 show an average of 1.6-fold increase in extraction of 2,4-DNT from glacial till us-ing HPCD solutions up to 2% HPCD. The slope of the plotsin Fig. 5 was determined to have an average value of 0.294(�� value), resulting in the �-value of 0.722 (� � 0.407).



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Figure 4. Relative extraction for cyclodextrin-enhanced desorp-tion of 2,4-DNT from montmorillonite.

Figure 5. Relative extraction for cyclodextrin-enhanced desorp-tion of 2,4-DNT from glacial till.

The linear increase in extraction indicates that as 2,4-DNTdesorbs from glacial till into the HPCD solution, it contin-ues to form a 1:1 inclusion with HPCD for up to 2% HPCDin an aqueous solution, which is in contact with the glacialtill soil. The �-value of 0.473 (less than 1.0) indicates thatthe desorption of 2,4-DNT from the glacial till soil was hin-

dered by soil–solute–solution interactions such as the inter-action between 2,4-DNT and soil organic matter, and thatthe expected increase in extraction of 2,4-DNT solely dueto the solute–solution interaction (enhanced solubility) be-tween 2,4-DNT and HPCD solutions did not occur. Thesorption of organic compounds onto soils containing organic


Figure 6. Sequential extraction of 2,4-DNT from montmorillonite soil.

matter has been attributed to sorption and uptake of the or-ganic compound by the soil organic matter matrix. The lackof increase in extraction from 2 to 5% HPCD was due tothe ineffectiveness of the additional 3% HPCD in solutionfor extraction of 2,4-DNT from glacial till, limited primar-ily by soil–solution interactions between the glacial till andthe 5% HPCD solution.

Sorption of HPCD in soils

The sorption or partitioning of HPCD in soil may be afactor affecting the desorption of 2,4-DNT from soils us-ing HPCD solutions. Using aqueous HPCD solutions, Koet al. (1999) have shown that no partitioning of HPCD oc-curred between water and kaolin. Using HPCD solutions



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Figure 7. Sequential extraction of 2,4-DNT from glacial till soil.

comparable to solutions used in our study for desorptionand extraction of 2,4,6-trinitrotoluene and its metabolitesfrom illite and topsoil, Sheramata and Hawari (2000) haveshown that HPCD did not adsorb onto illite (a pure clay)or topsoil. Due to its high aqueous solubility, HPCD is acyclodextrin with low surface activity for adsorption ontosoils. Badr et al. (2004) have shown minimal adsorptionof HPCD onto silty soils containing up to 5% organic mat-ter.

Because the sorption of HPCD onto illite and kaolin(two mineral soils) has not been observed, the sorptionof HPCD onto montmorillonite would be unlikely in this study. The sorption or partitioning of HPCD in thesoil organic matter could possibly contribute to a decreasein effectiveness of different HPCD solutions for extrac-tion of organic soil contaminants. In our study, becausethere was no increase in extraction of 2,4-DNT fromglacial till from 2% HPCD to 5% HPCD, the sorption ofsome HPCD from the 5% HPCD solution onto soil or-ganic matter contained in the glacial till may have con-tributed to the lack of increase in desorption of 2,4-DNTusing 5% HPCD.

Sequential extraction of 2,4-DNT from soils

To increase the extraction efficiency of HPCD solutionsfor removal of 2,4-DNT from soils, three different strate-gies for sequential extraction of soils were carried out. Se-quential extractions were carried out in several stages usingthe intermediate soil:solution extraction ratio of 1:10 (g/mL)to avoid using larger volumes of solution, where the soil wasextracted with HPCD solutions followed by water rinsestages. Because the extraction kinetics results for montmo-rillonite and glacial till presented in Fig. 3 had shown thatmost of the extractable 2,4-DNT was removed from soilwithin 1 h of extraction, the soils were extracted for 1 h ineach extraction stage of the sequential extractions. Becausethe soil extraction data presented in Fig. 2b show that the2% HPCD solution was an effective extraction solution forglacial till, sequential extractions of glacial till were carriedout with the 2% HPCD solution. Although the soil extrac-tion data from Fig. 2a show higher extraction of 2,4-DNTfrom montmorillonite using the 5% HPCD solution, the 2%HPCD solution was used in sequential extraction of 2,4-DNT from montmorillonite to optimize the efficiency of thesequential extraction and to compare the extraction frommontmorillonite to extraction from glacial till using the sameextracting solution. The sequential extractions were carriedout using the following sets of sequential stages: five-stageextraction with water, five-stage extraction (the first stagewith 2% HPCD followed by a second-stage water rinse andthe third stage with 2% HPCD followed by two water rinsestages), and five-stage extraction (three stages with 2%HPCD followed by two water rinse stages).

The results for the sequential extraction of 2,4-DNT frommontmorillonite and glacial till soils are shown in Figs. 6and 7, respectively. The results from Figs. 6a and 7a indi-cate that five-stage extraction with water alone resulted inthe lowest cumulative removal of 2,4-DNT from the mont-morillonite (30%) and glacial till (33%), respectively. Theresults from Figs. 6b and 7b show a marked improvementin removal of 2,4-DNT from montmorillonite (53%) andglacial till (68%), respectively, with the addition of twostages of extraction with 2% HPCD with an intermediatewater rinse stage between the first and second extractionstages with 2% HPCD. Three-stage sequential extractionswith 2% HPCD removed 55.2 and 65.2% of 2,4-DNT frommontmorillonite and glacial till soils, respectively, whereasthree-stage extractions with water removed only 28.3 and30.8% of 2,4-DNT from the two soils, respectively. Thefive-stage sequential extraction with 2% HPCD shown inFigs. 6c and 7c removed the most 2,4-DNT from montmo-rillonite (64%) and glacial till (75%), respectively. The re-sults of the fivestage sequential extractions shown in Figs.6 and 7 show that extractions using 2% HPCD were supe-rior to extraction using water alone (Figs. 6a and 7a), wherethere was no significant extraction after the third extractionstage with water.

The results from the single batch extractions and mul-tistage sequential extractions for the montmorillonite andglacial till soils show that more 2,4-DNT was removedfrom glacial till using the 2% HPCD solution. Althoughthe glacial till contained organic matter, the interaction be-tween 2% HPCD solution, glacial till, and 2,4-DNT wasmore effective than the interaction between 2% HPCD so-lution, montmorillonite, and 2,4-DNT, conducive to thegreater removal of 2,4-DNT from glacial till. The soilproperty data presented in Table 1 show that the particlesize distributions for the montmorillonite and glacial tillsoils are similar; however, montmorillonite has a largespecific surface area (220 m2/g) and swells after contactwith the aqueous solutions, increasing the contact surfacearea between the extracting solution and soil. Thus, thestronger retention of 2,4-DNT by montmorillonite and thelower extraction of 2,4-DNT using the 2% HPCD solu-tion could be due to the high specific surface area of mont-morillonite soil particles.

CONCLUSIONS

In single batch extractions, 1 and 2% HPCD solutionswere as effective as 5% HPCD solutions for removal of2,4-DNT from kaolin and glacial till soils, respectively,whereas the 5% HPCD solution was more effective than2% HPCD for removal of 2,4-DNT from montmorillonite.The 2% HPCD solution removed more 2,4-DNT fromglacial till than from montmorillonite. As a soil washing


strategy, five-stage sequential extraction of 2,4-DNT frommontmorillonite and glacial till soils using three stages ofextraction with 2% HPCD followed by two water rinsestages was more successful than five-stage extraction withwater alone, removing 75 and 64% of 2,4-DNT contami-nation from the glacial till and montmorillonite soils, re-spectively. In remediation of soils contaminated with mu-nitions wastes such as 2,4-DNT, a greater than twofoldincrease in removal of contaminant using 2% HPCD canbe an appreciable improvement in ex situ remediation ofcontaminated soils.

AUTHOR DISCLOSURE STATEMENT

The authors state that no competing financial interests exist.

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cyclodextrin-enhanced extraction and removal of 2,4-dinitrotoluene from contaminated soils

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