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J. Ind. Eng. Chem.,Vol. 13, No. 4, (2007) 650-656

Ultrasonic-Assisted Extraction to Release Heavy Metals from

Contaminated Soil

Seon-Suk Hwang, Joon-Seok Park*

, and Wan Namkoong**

Department of Environmental Engineering, College of Engineering, Konkuk University, Seoul 143-701, Korea

*Department of Environmental Disaster Prevention Engineering, College of Engineering, Kangwon National

University, Kangwon-do 245-711, Korea

**Konkuk University Innovative Environmental Technology Center, Konkuk University, Seoul 143-701, Korea

Received January 24, 2007; Accepted February 14, 2007

Abstract: The soil used in this research was obtained from a heavy metal-contaminated site near a Pb-smelting plant. For ultrasonic-assisted extraction, citrate and ethylenediaminetetraacetic acid (EDTA) were used as

leaching solutions. When using 0.05 and 0.1 M citrates, the highest extraction efficiency was obtained at 30

W. For both citrate and EDTA, the efficiency increased with sonic time and showed the maximum at 12 min.

At the same concentration (0.05 M), EDTA was better than citrate at extraction. Despite the short extraction

time, the extraction efficiencies of metals with sonication were higher than those of soil washing for both 0.05M citrate and 0.05 M EDTA. Extraction of metallic elements from contaminated soil could be enhanced with

the aid of ultrasonic treatment.

Keywords: ultrasonic-assisted extraction, contaminated soil, heavy metal

Introduction1)The deposition of metal-rich mine tailings, metal smelt-

ing, leather tanning, electroplating, emissions from gasexhausts, energy and fuel production, down-wash from

power lines, intensive agriculture, and sludge dumping

are the human activities that contaminate soil systems

with the largest amounts of toxic metals [1,2]. The list of

sites contaminated with toxic metals grows larger every

year, presenting a serious health problem and a formida-

ble danger to the environment.

Determination of the exact forms of certain elements in

natural systems is challenging and time-consuming be-cause identifying the exact species usually requires so-

phisticated instrumental techniques [3]. Various sequen-

tial extraction methods have been widely used for the de-

termination of metal behavior in environmental solid

materials. One of the main limitations of sequential ex-

traction procedures is that they are extremely time-

consuming. Extraction of metals from solid samples us-ing ultrasonic treatment is both fast and efficient [4].

To whom all correspondence should be addressed.

(e-mail: [email protected])

Ultrasonic processing applies intense, high-frequency

sound to liquids, producing intimate mixing and power-

ful chemical and physical reactions [1]. The process of

cavitation is, in effect, cold boiling and results fromthe creation of chemical and physical reactions, such as

those of surfactancy, which is why ultrasonic processing

is a preferred extraction technique. Intensity is a measure

of the energy available per unit volume of liquid and is

directly related to amplitude. It is the intensity of cav-

itation that accelerates physical and chemical reactions,

not the total power applied to the system. Therefore, pa-

rameters such as time, frequency, and volume of sample

ought to be optimized.Soil washing technology has been applied to treat met-

al-contaminated sites. Soil washing systems offer the

greatest promise for application to soils contaminated

with a wide variety of heavy metal and organic con-

taminants [5]. In soil washing, sequential washing steps

may be needed to enhance treatment efficiency, which is

time-consuming and brings about an increase of reagentaddition and wastewater generation. Sonication processes

have been applied limitedly to pretreatment for metal

analysis and pre-extraction of metals, including Cu, Pb,

Ni, and Zn, in order to recover precious metals [6].

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Ultrasonic-Assisted Extraction to Release Heavy Metals from Contaminated Soil 651

Table 1. Experimental Conditions

Item Contaminated soil

Texture Sandy loam

Sand (20.05 mm) (%) 57.6

Silt (0.050.002 mm) (%) 26.2Clay (< 0.002 mm) (%) 16.2

Moisture content (%) 0.7

Field capacity (%) 35

Volatile solids (%) 3.7

pH 7.5

Cation exchange capacity (meq/100 g) 17.3

The use of ultrasound power has been investigated tospeed up sequential extraction methods because it has

long been recognized that the cavitational effect created

by ultrasound waves can break down the particle size,

exposing a fresh surface and aggressively agitating thesolution system [7]. When a suspension of solid particles

is subjected to treatment with ultrasound, particle dis-

persion can take place, which, in turn, causes an increase

in the surface area available for the reaction. When ex-traction applications of ultrasound are concerned, particle

fragmentation can enhance the ability of the extractant to

leach metals [3]. Ultrasonic-assisted extraction has not

been studied for remediation of heavy metal-contamin-

ated soil. Ultrasonic-assisted extraction could enhance

the treatment efficiency and shorten the time required for

washing contaminated soil. Therefore, in this study we

estimated the possibility of using ultrasonic treatment for

washing contaminated soil.

Experimental

Contaminated Soil

The soil for this research was obtained from a heavy

metal-contaminated site near a Pb-smelting plant inGoyang city, Kyungki-do. Soil near the plant, which had

been operated for 30 years, was found to be highly con-

taminated with Pb and other heavy metals. After being

sampled, the soil was air-dried and passed through a

2-mm sieve to remove large soil fractions, such as stoneand gravel. Table 1 shows the characteristics of the soil.

The texture of the soil was classified as a typical sandy

loam (the portions of sand, silt, and clay in the soil were57.6, 26.2, and 16.2 %, respectively). The cation ex-

change capacity (CEC) of the soil was 17.3 meq/100 g of

dry soil, which was in the range of natural soils having

CEC values of 10 to 30 meq/100 g [8].

Experimental Apparatus and Conditions

A 3.0 g sample of soil was mixed with a leaching sol-

ution in a ratio of 1:10 (W/V). Citrate and ethyl-

Figure 1. Laboratory apparatus used for ultrasonic extraction of

heavy metals.

enediaminetetraacetic acid (EDTA) were used as leach-ing solutions. In a previous study [9], it was shown that

the extraction efficiency of citrate was lower than those

of EDTA and HCl.The ultrasonic system for this research consisted of an

ultrasonic generator, a piezoelectric transducer, and an

acoustic horn, as shown in Figure 1. Ultrasonic irradi-

ation at 20 kHz was carried out using an ultrasonic sys-

tem from Mirae Ultrasonic Tech. Co., Korea. The gen-

erator could be controlled in a power range of 0100 W(030 W/cm

2). Sonication was performed with a horn

of 2-cm diameter and 18-cm length. The bottom of thehorn was immersed 0.5 cm beneath the surface of the

sample solution. The experiment was carried out with thesonicated solutions open to the atmosphere. Ultrasonic

power of 10 to 40 W was applied for up to 12 min.

Analysis

The initial concentration of heavy metals in the con-

taminated soil and the background soil were analyzed us-

ing the methods of Chlopecka [10] and Ure [11]. Hot

acidic digestion was employed in soils with acids such as

HNO3, HClO4, and HF. HNO3 (10 mL) was added to a

Teflon beaker containing 1.0 g of soil; the beaker was

heated until the solution was concentrated to a small vol-

ume, and then cooled to room temperature. After the ad-dition of 5 mL of HNO3, 5 mL of HClO4, and 10 mL of

HF, the solution was heated for 30 min with white fume

generation. After the addition of HCl (1:1, V/V; 10 mL),

the solution was heated for 10 min, and then cooled to

room temperature. The final volume of the solution was

adjusted to 100 mL with distilled water. Fractional con-

centration of heavy metals was also analyzed by sequen-tial extraction schemes used in Tessier and coworkers

research [12].

The determination of Pb, Cu, Zn, and Cd in the ex-

tracted solution was carried out using an Atomic Ab-

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Seon-Suk Hwang, Joon-Seok Park, and Wan Namkoong652

Table 2. Concentrations of Pb, Cu, Cd, and Zn for the Contaminated Soil and Background Soil

Item Pb (mg/kg) Cu (mg/kg) Cd (mg/kg) Zn (mg/kg)

Contaminatedsoil

Exchangeable 366*

(2.4)**

0.31 (0.5) 1.58 (9.9) 1.33 (0.5)

Carbonate 6082 (40.6) 4.30 (6.6) 1.31 (8.2) 18.62 (7.3)

Reducible 2330 (15.5) 10.96 (16.4) 0.85 (5.3) 100.46 (39.3)

Oxidizable 323 (2.2) 12.27 (18.9) 0.28 (1.7) 37.22 (14.5)

Residual 5899 (39.3) 37.44 (57.6) 11.99 (74.9) 98.38 (38.4)

Total 15000993***

653.7 161.4 25612

Background soil 60 24 0.9 60

Permission standard****

400 50 1.5 300

*Mean concentration of 15 samples.

**( ) = % Portion relative to total concentration.

***Relative standard deviation.

****Soil Contamination

Care Permission Standard for industrial region in Soil Environment Conservation Act.

sorption Spectrophotometer (Shimadzu AA-6501F, Ja-

pan) equipped with an acetylene-air flame. Hollow cath-ode lamps (Shimadzu) were used as a radiation source

for all the studied elements. The instrumental parameters

employed were a spectral bandwidth of 0.2 nm for Pb

and Cd and 0.5 nm for Cu and Zn. The wavelengths were

217.0, 324.8, 213.9, and 228.8 nm for Pb, Cu, Zn, andCd, respectively.

Two-constant Rate Kinetic Model

Zn adsorption or desorption processes have been basedmainly on the study of equilibrium conditions using ther-

modynamic approaches [13]. The thermodynamic ap-

proach can predict only the final state of a soil system

from an initial non-equilibrium state, while the analysisof the kinetics may yield important information concern-

ing the nature of the reaction at a given time. Zinc de-

sorption kinetics have been described by a two-constant

rate equation by Kuo and Mikkelsen [14] as

Qt= atb

where Qt is the amount of Zn desorbed by EDTA (mg

Zn/kg) aftert(sec) period of extraction, a is the initial Zn

desorption rate constant (mg Zn/kg/sec)b, b is the de-

sorption rate coefficient (mg Zn/kg)-1

, and t is the ex-

traction time (sec). An increase in the value of a and a

decrease in b probably indicates an increase in the rate ofZn desorption from the soils.

Results and Discussion

Initial Heavy Metal Concentrations in Contaminated

Soil

The mean concentrations of Pb, Cu, Cd, and Zn in the

contaminated soil and in the background soil are sum-

marized in Table 2. The concentrations of Pb, Cu, Cd,

and Zn in the contaminated soil were 15000, 65, 16, and

256 mg/kg, respectively. Pb was present at the highestconcentration among all of the heavy metals. It is ob-

vious that the plant affected the neighboring soil quality.

The Pb concentration of the contaminated soil was 250

and 38 times higher than the 60 mg/kg of the background

soil and the 400 mg/kg of the Soil Contamination CarePermission Standard for industrial region in Soil Envi-

ronment Conservation Act, respectively.

The distribution of heavy metals in the contaminated

soil according to the chemical combined form is also pre-

sented in Table 2. The residual fraction in heavy metals

was ca. 40 % for Pb and Zn, 60 % for Cu, and 75 % for

Cd. The distributed characteristics of the exchangeable,

carbonate, reducible, and oxidizable fractions in eachmetallic element were different. In the case of Pb, carbo-

nate and reducible fractions were high relative to ex-

changeable and oxidizable fractions. In the case of Cd,

exchangeable, carbonate, reducible, and oxidizable frac-

tions were lower than 10 %. This situation may be due to

the high residual fraction (ca. 75 %) of Cd. Ma and Rao

reported that Cd was present mainly in residual fraction

when the natural concentration was lower than 50 mg/kg[15].

The chemical combined fraction from sequential ex-

traction analysis could be classified into two groups:

non-detrital and detrital fractions [16]. Although these

fractions (the five-step extraction scheme) are opera-tional and caution is warranted in mechanistic inter-

pretations, it is convenient to broadly consider two frac-

tion categories. Non-detrital metals are displaceablewithout solid phase dissolution. Detrital metals are re-

leased into solution only if structural decomposition of

minerals occurs. The nondetrital fraction includes the ex-

changeable, carbonate, and oxidizable fractions in metals

and represent the portion of the soil metal that is poten-

tially leachable and bioavailable. The reducible and re-

sidual metals will not be environmentally available under

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Table 3.Non-detrital and Detrital Fractions (%) of Pb, Cu, Cd,

and Zn in the Contaminated Soil

Fraction Pb Cu Cd Zn

Non-detrital 45.2 26.0 19.8 22.3

Detrital 54.8 74.0 80.2 77.7

Figure 2. Effect of sonication power on extraction of metals.

normal conditions, and are termed detrital because their

release requires solid phase dissolution. Therefore, it ismore difficult to extract the detrital heavy metal fraction

from contaminated soil relative to the non-detrital heavy

metals. The non-detrital fraction of Pb was the highest

(45.2 %) among the metals. Apart from the case of Pb,

the non-detrital fractions of Cu, Cd, and Zn were below

20 % (Table 3). From this result, we predicted that Cu,

Cd, and Zn could not be extracted simply.

Effect of Sonication Power and Time on Extraction

Efficiency

The effect of the sonication power on the extraction of

metals is provided in Figure 2. A low metal extraction ef-

ficiency was observed in 0.05 and 0.1 M citrate leaching

solutions. Despite the concentration of Pb being the high-

est in this metal-contaminated soil, the extraction effi-

ciency of Pb was the highest among the metals Pb, Cu,Cd, and Zn. As previous mentioned, this situation might

Figure 3. Effect of sonication time on extraction of metals with

leaching solutions of 0.05 and 0.1 M citrate.

be due to the fact that the non-detrital fraction of Pb was

the highest (45.2 %) among these metals. The extraction

efficiency increased with an increase of the sonicationpower in 0.05 M citrate [Figure 2(a)]. The extraction effi-

ciency at 40 W was 714 % higher than that at 10 W.The highest extraction efficiency was observed at 30 W

for 0.1 M citrate [Figure 2(b)]. For both 0.05 and 0.1 M

citrates, high extraction efficiency was mainly shown at

30 W.

Figure 3 shows the effect of the sonication time on ex-

traction of metals with leaching solutions of 0.05 and 0.1

M citrate. The sonication power was fixed at 25 W. The

extraction efficiency increased slightly with the soni-cation time for 0.05 and 0.1 M citrates. However, a great-

er increase of the extraction efficiency was observed in

0.1 M citrate for Pb. When the sonication time was over

5 min in 0.05 and 0.1 M citrates, the extraction efficiency

was ca. 10 % higher than those after 1 and 3 min. Pb was

extracted the most among these metallic elements.

For 0.01 and 0.05 M EDTA, the effect of the sonication

time on the removal efficiency of metals is presented inFigure 4. The sonication power was fixed at 25 W. In

this case, the extraction efficiency increased with the

sonication time and was highest at 12 min. Visnen and

coworkers reported that the optimum ultrasonic ex-

traction time was 9 min for releasing metals [17].

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Figure 4. Effect of sonication time on extraction of metals with

leaching solutions of 0.01 and 0.05 M EDTA.

Table 4. Kinetic Constant B Based on Two-constant Rate-

based Model

Item

0.05 M Citrate 0.05 M EDTA

Sonication

(min)-1

Soil washing

(min)-1

Sonication

(min)-1

Soil washing

(min)-1

Pb 0.2553 0.1443 0.1010 0.1444

Cu 0.1206 0.1079 0.1573 0.1449

Cd 0.1066 0.0994 0.1170 0.1003

Zn 0.2535 0.2211 0.3442 0.2247

At the same concentration of 0.05 M, the extraction ef-

ficiency of the metals for citrate was compared with that

for EDTA (Figure 5). The extraction efficiencies of Pb,

Cu, and Cd for EDTA were much higher than those of

citrate, except for Zn. The extraction efficiency of Pb forEDTA was 2.5 times higher in comparison to that of

citrate. Consequently, EDTA was better than citrate for

metal extraction from contaminated soil.

Two-constant Rate-based Kinetics

The two-constant rate-based kinetics for Pb, Cu, Cd,

and Zn, based on two-constant rate model, are provided

in Figures 69 and Table 4. The concentrations of cit-rate and EDTA used were the same (0.05 M). The ki-

netics of ultrasonic treatment are presented with that of

soil washing at the same concentration. Data for soil

Figure 5. Removal efficiency of metals with 0.05 M citrate and

0.05 M EDTA after a 12-min sonication time.

Figure 6. Two-constant rate-based model for Pb in sonication

and soil washing with 0.05 M citrate and 0.05 M EDTA.

washing were obtained from the previous research by

Hwang and coworkers [9]. The kinetic model in this

research is given by C = AtB

, whereA is the extraction

efficiency (%), B is the desorption rate constant (min-1

),

C is the extraction efficiency (%) at time t, and t is the

extraction time (min). The model is linearly transformedto the following equation.

Log C = Log A + BLog t

Except of Pb, for sonication with 0.05 M EDTA, the

two-constant rate-based kinetic model described the ex-

traction reaction of metals with high correlation co-

efficients (R2

= 0.780.99). The kinetic constant forsonication was similar to, or slightly higher than, that forsoil washing. In Pb with 0.05 M EDTA, the kinetic con-

stant (0.144 min-1

) for soil washing was higher than that

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Figure 7. Two-constant rate-based model for Cu in sonication


Figure 8. Two-constant rate-based model for Cd in sonication


(0.101 min-1

) for sonication (Table 4), which might be

due to the fact that the non-detrital fraction of the

contaminated soil was as high as 45.2 % and was ex-

tracted easily, even through soil washing with EDTA.Despite the short extraction time, extraction efficiencies

of metals with sonication were higher than those of soil

washing for both 0.05 M citrate and 0.05 M EDTA

(Figures 69). For example, when the extraction timewas 12 min (log t = 1.079 min), the values of log

(Extraction Efficiency) of Pb for sonication and soil

washing were 1.441 and 1.036, respectively (Figure 6).

The value of log (Extraction Efficiency) for sonication atan extraction time of 12 min (log t = 1.079 min) was

slightly higher than that (1.408) for soil washing for 360

Figure 9. Two-constant rate-based model for Zn in sonicationand soil washing with 0.05 M citrate and 0.05 M EDTA.

min (log t = 2.556 min). This result indicates that the

ultrasonic-assisted extraction could help to enhance the

extraction of metals from contaminated soils and to

shorten the extraction time greatly. Other researchers

have reported that ultrasonic extraction could shorten

extraction times during pretreatment for metal analysis[1,17,18].

Conclusions

The Pb, Cu, Cd, and Zn concentrations of the con-

taminated soil used in this research were 15000, 65, 16,and 256 mg/kg, respectively. The residual fraction in

heavy metals was ca. 40 % for Pb and Zn, 60 % for Cu,

and 75 % for Cd. The non-detrital fraction of Pb was the

highest (45.2 %) among these metals, which indicates

that Pb could be extracted more simply than the other

metals. When using 0.05 and 0.1 M citrate, the highest

extraction efficiency was obtained at 30 W. In both cit-

rate and EDTA, the extraction efficiency increased withthe sonication time; it was highest at 12 min. At the same

concentration (0.05 M), extraction with EDTA showed

higher efficiency than that with citrate. The two-constantrate-based kinetic model described the extraction re-

action of metals with high correlation coefficients (R2

=

0.780.99). Despite the short extraction time, the ex-traction efficiencies of metals with sonication were high-

er than those with soil washing for both 0.05 M citrateand 0.05 M EDTA. Extraction of metallic elements from

contaminated soil could be enhanced with the aid of ul-

trasonic treatment.

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References1. A. Marn, A. Lpez-Gonzlvez, and C. Barbas,Anal.

Chim. Acta, 442, 205 (2001).

2. C. Jeon and S. H. Yeom,J. Ind. Eng. Chem., 12, 362(2006).

3. T. G. Kazi, M. K. Jamali, A. Siddiqui, G. H. Kazi, M.

B. Arain, and H. I. Afridi, Chemosphere, 63, 411

(2006).

4. C. Bedicho and I. Lavilla, in Encyclopedia ofSeparation Science, I. D. Wilson, E. R. Adlard, M.

Cooke, and C. F. Poole, Eds., pp. 4421-4426,

Academic Press, London (2000).

5. H. M. Freeman and E. F. Harris, Hazardous Waste

Remediation: Innovative Treatment Technologies,

pp. 103-112, Tehnomic Publishing Co., Inc.,

Lancaster (1995).

6. K. M. Narayana, K. M. Swamy, R. K. Sarveswara,and J. S. Murty,Min. Process. Ext. Metallurgy Rev.,

16, 239 (1997).

7. T. J. Mason, in Sonochemistry: The Uses of

Ultrasound in Chemistry, T. J. Mason, Ed., p. 5,

Royal Society of Chemistry, London (1990).

8. R. C. Loehr, inLand Disposal of Hazardous Wastes,

Hazardous Waste Management Engineering, E. J.

Martin and J. H. Johnson, Eds., pp. 365-439, VanNostrand Reinhold, New York (1987).

9. S. S. Hwang, S. S. Park, and W. Namkoong, J.

Korean Soc. Env. Eng., 26, 1181 (2004).

10. A. Chlopecka, Sci. Total Environ., 188, 253 (1996).

11. A. M. Ure, in Method of Analysis for Heavy Metals

in Soils, B. J. Alloway, Ed., pp. 40-80, Blakckie &

Sons, London (1990).

12. A. Tessier, P. G. C. Campbell, and M. Bisson,

Analy. Chem., 51, 844 (1979).

13. Y. P. Dang, R. C. Dalal, D. G. Edwards, and K. G.

Tiller, Soil. Sci. Soc. Am. J., 58, 1392 (1994).

14. S. Kuo and D. S. Mikkelson, Plant Soil, 56, 355

(1980).

15. L. Q. Ma and G. N. Rao, Environ. Qual., 26, 259

(1997).

16. H. A. Elliott and N. L. Shastri, Water Air SoilPollut., 110, 335 (1999).

17. A. Visnen, R. Suontamo, and J. Silvonen, Anal.

Bioanal. Chem., 373, 93 (2002).

18. B. Prez-Cid, I. Lavilla, and C. Bendicho,Fresenius

J. Analy. Chem., 363, 667 (1999).

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