Electrokinetic extraction of lead from kaolinites:II. Experimental investigation

Cheng-non Hsu • Albert T. Yeung •

Rajendra M. Menon

Published online: 14 January 2011

� Springer Science+Business Media, LLC 2011

Abstract This is the second paper of two companion

papers presenting the results of laboratory bench-scale

experimental studies on electrokinetic extraction of lead

from two different kaolinites. The theoretical formulation

and numerical simulation of the process are presented in

the first paper. Two different kaolinites were used in the

study: (1) Georgia kaolinite and (2) Milwhite kaolinite. The

lead spiked in Georgia kaolinite was highly mobilized and

effectively extracted by the technique as the pH in the soil

was significantly lowered by the electrokinetic process.

Milwhite kaolinite has a much higher acid/base buffer

capacity, and the required acidic environment could not be

developed. As a result, removal of the lead spiked in

Milwhite kaolinite was minimal. Comparison between

simulations and experimental results is also presented.

Factors affecting the cleanup efficiency of the process and

potential enhancement techniques are also discussed.

Keywords Electrokinetic extraction � Experimental

studies � Georgia kaolinite � Milwhite kaolinite �Acid/base buffer capacity of soil � Soil pH

1 Introduction

Approximately 15% of uncontrolled hazardous waste sites

in the United States have lead-related contamination

problems (Ellis et al. 1986). Although the situation of lead

poisoning in the United States is improving, it remains a

problem in many parts of the world. However, many

existing technologies have been proven to be ineffective in

remediating heavy metal-contaminated fine-grained soils

due to the low hydraulic conductivity of the soil and strong

interactions between heavy metal contaminants and soil

particle surfaces (Yeung 2009a).

Electrokinetic processes, phenomena first observed in

1809 by Reuss (Yeung 1994, 2006b), have been studied

intensively during the past two decades for their potential

in removing heavy metal contaminants from fine-grained

soils. Electrokinetic phenomena occur when two different

phases move relative to each other, and an electric diffuse

double layer exists at the interface between the two

phases (van Olphen 1977; Yeung 1992). They include

electroosmosis, electrophoresis, streaming potential, and

sedimentation potential. Some researchers have also

included ionic migration as an electrokinetic process

(Lageman et al. 2005; Yeung 2006b). Among these phe-

nomena, electroosmosis and ionic migration are the fun-

damental mechanisms contributing to the transport of

contaminants in the liquid phase of a contaminated soil

when a direct-current (dc) electrical potential is imposed

across the soil (Menon 1996; Yeung 2008, 2009b). When

the soil is subjected to a dc electric field, migration of

pore fluid is generated by electroosmosis and movement

of ions relative to the pore fluid is caused by ionic

migration. The combined effects of these two contaminant

removal mechanisms control the movement of ionic and

non-ionic contaminants in the liquid phase. Diffusion,

C. Hsu

Rikulau International Co. Ltd, No. 70-9 Sing An Road,

Ta-Jia Township, Taichung County, Taiwan

e-mail: chengnon@rikulau.com

A. T. Yeung (&)

Department of Civil Engineering, The University of Hong Kong,

Pokfulam Road, Pokfulam, Hong Kong

e-mail: yeungat@hku.hk

R. M. Menon

Regional Income Tax Agency, 2274 Demi Drive, Twinsburg,

OH 44087, USA

e-mail: mrmenon@hotmail.com

123

Environmentalist (2011) 31:33–38

DOI 10.1007/s10669-010-9298-1

however, is significant only when electroosmosis is sup-

pressed (Probstein and Hicks 1993).

The technique of electrokinetic extraction has been

applied successfully in laboratory bench-scale experiments

to mobilize and to remove organic contaminants such as

phenol (Acar et al. 1992; Shapiro and Probstein 1993;

Gopinath 1994; Yang and Long 1999) and gasoline hydro-

carbons (Bruell et al. 1992; Maini et al. 2000); and inorganic

contaminants such as Cu(II), Pb(II), Hg(II), and Cd(II)

(Hamed et al. 1991; Pamukcu and Wittle 1992; Eykholt and

Daniel 1994; Yeung et al. 1996; Sawada et al. 2003; Suer

and Allard 2003; Yeung and Hsu 2005) spiked in clayey soil

specimens. Banerjee et al. (1991), and Lageman and

Godschalk (2007) conducted pilot-scale field electrokinetic

extraction experiments and obtained very promising results.

In all these laboratory and field experiments, mobilization

and extraction of sorbed contaminants depend on the

development of an acid front to desorb the contaminants

from soil particle surfaces (Yeung 2006a). The solubilized

contaminants are then transported by electroosmosis, ionic

migration, diffusion, and possibly hydraulic advection.

Development of the acid front is caused by migration of H?

generated at the anode from electrolytic decomposition of

water into the system (Acar et al. 1990) and the interactions

between the soil and ions in the system (Yeung and Datla

1995; Yeung et al. 1996, 1997a; Yeung 2009b). Georgia

kaolinite was used in most of these laboratory electrokinetic

extraction experiments. It is a well-characterized soil well

known for its low acid/base buffer capacity and cation

exchange capacity (van Olphen and Fripiat 1979). Thus, a

low soil pH of 2–3 can be obtained easily during the

experiment, resulting in a very high removal rate of even

strongly sorbed chemical species such as Pb(II) and Cu(II).

However, the pH of any soil of high acid/base buffer

capacity and cation exchange capacity may not be lowered

that easily (Gu et al. 2009a). As a result, most heavy metal

contaminants will remain sorbed on soil particle surfaces,

rendering electrokinetic extraction inefficient.

In this study, the efficiency of electrokinetic extraction

technique to remove spiked Pb(II) from two kaolinitic

soils: (1) Georgia kaolinite and (2) Milwhite kaolinite were

evaluated. The acid/base buffer capacities of the two soils

were significantly different. Parameters measured experi-

mentally are also used as input data for the numerical

model developed to simulate the process. Factors affecting

the cleanup efficiency of the process and potential

enhancement techniques are also discussed.

2 Soil properties

Georgia kaolinite and Milwhite kaolinite were used to

develop a better understanding of the physicochemical

soil–lead interactions and to evaluate their different

behavior during an electrokinetic extraction process.

Georgia kaolinite is a well-characterized soil with a low

acid/base buffer capacity and a cation exchange capacity

(CEC) of approximately 20 mmol/kg (van Olphen and

Fripiat 1979). Milwhite kaolinite is a commercial product

from Patria Packaging, Inc., Valdosta, Georgia. It is red-

dish brown in color and has a higher CEC of 29 mmol/kg

and a much higher acid/base buffer capacity (Yeung et al.

1996). Pertinent physicochemical properties of the two

kaolinites are tabulated in Table 1 of the first paper of these

two companion papers. More detailed descriptions of the

soils are given by Yeung et al. (1996), Yeung and Hsu

(2005).

3 Experimental design and setup

This experimental investigation includes batch tests and

bench-scale electrokinetic extraction experiments. The

batch tests were designed and performed to characterize the

soil and soil-contaminant interactions and to lay the foun-

dation for bench-scale electrokinetic extraction experi-

ments. They include (1) determination of acid/base buffer

capacity of the soil and (2) sorption/desorption character-

istics of the soil as a function of pH. In the bench-scale

electrokinetic extraction experiments, the feasibility of the

technique to remediate lead-contaminated soil under dif-

ferent operating conditions was evaluated. The results

obtained were also used to evaluate the numerical model

developed.

The schematic of the setup of the electrokinetic

extraction experiment is shown in Fig. 1. The specimen

cylinder is made of acrylic of 152.4 mm in length and

76.2 mm in internal diameter. Detailed descriptions of

specimen preparation, experimental setup, and testing

Fig. 1 Schematic of the electrokinetic extraction apparatus

34 Environmentalist (2011) 31:33–38

123

procedures are given by Yeung et al. (1997b). The

parameters of the experiments are tabulated in Table 2 of

the first paper of these two companion papers.

4 Results and discussion

4.1 Acid/base buffer capacity

Acid/base buffer capacity of a soil is determined by

titrating the soil with a strong acid/base. In this study, 1 M

HNO3 and 1 M NaOH were used. The volume of acid/base

added to the soil is plotted versus the resulting soil pH in

Fig. 2. The slope of the curve at each pH value gives the

acid/base buffer capacity of the system at that pH. It can be

observed that the slope of Milwhite kaolinite curve is much

steeper than that of the Georgia kaolinite curve at all pHs.

Thus, it takes much more acid/base in Milwhite kaolinite

than in Georgia kaolinite to cause an equal change in pH.

Moreover, the acid/base buffer capacities of both soils are

dependent on pH, and it is more difficult to change the soil

pH in both low and high pH ranges.

4.2 Sorption/desorption of lead onto/from the kaolinite

particle surfaces

Soil pH has a profound influence on the sorption/desorption

of lead onto/from kaolinite particle surfaces. The results of

batch tests on sorption/desorption of lead onto/from sur-

faces of the two kaolinites are presented in Fig. 3. It can be

observed that only approximately 20–30% of lead is sorbed

onto the surface of kaolinites in the pH range of 2–3.

However, almost all the lead disappears from the liquid

phase as the soil pH increases to approximately 5. When

the lead species are not in the liquid phase, they become

immobile and are very difficult to be removed from the

subsurface.

4.3 Electrokinetic extraction

The acid/base buffer capacity of a soil has tremendous

impact on the soil pH distribution during electrokinetic

extraction. This impact can be observed easily in Fig. 4

where the final pH distributions obtained in two electro-

kinetic extraction experiments are presented. Georgia

kaolinite was used in Test EK-1. The soil pH was lowered

from the initial value of 3.45 to approximately 2 in most

sections of the soil specimen in 120 h. However, 96 h of

electrokinetic treatment could not lower the pH of Mil-

white kaolinite in most sections of the soil specimen in Test

EK-2 due to the higher acid/base buffer capacity of the soil.

The final pH was thus still at the initial value of 4.4. Very

small pH changes occurred in the Milwhite kaolinite

specimen in the vicinity of the electrodes. The volume of

electroosmotic flow in Test EK-2 was also much less than

that of Test EK-1, resulting in smaller amount of H? and

OH- ions migrating into the soil. Moreover, the direction

of electroosmotic flow in Test EK-2 was from the cathode

toward the anode which would further reduce the amount

of H? ions migrating into the soil.

The final pH distributions of the two experiments pre-

dicted by the numerical model are also shown in Fig. 4. It

can be observed that the pH distributions predicted by the

model are in good agreement with the experimental mea-

surements. Thus, the assumptions made in the development

of the model and the modeling approach are plausible.

Since a low pH environment can be developed in

Georgia kaolinite by the electrokinetic extraction process,

the lead spiked could be mobilized and removed from the

soil as shown in Fig. 5. The residual concentration of lead

in the specimen is considerably lower than the initial

concentration of 12.065 mol/m3 after 120 h of electroki-

netic treatment. However, the results are completely dif-

ferent in Milwhite kaolinite. As the pH in Milwhite

kaolinite could not be lowered, the lead was sorbed on soil

Fig. 2 Acid/base buffer capacity curves of Georgia kaolinite and

Milwhite kaolinite Fig. 3 Sorption curves of Georgia kaolinite and Milwhite kaolinite

Environmentalist (2011) 31:33–38 35

123

particle surfaces as shown in Fig. 3 and thus not removed

after 96 h of treatment. As a result, the residual concen-

tration of lead in the Milwhite kaolinite specimen is

practically identical to the initial concentration as shown in

Fig. 5. The comparison between the final total lead con-

centration distribution predicted by the model and that

measured by experiments is also presented in Fig. 5. It can

be observed that they are in good agreement.

The comparison between the final voltage distributions

predicted by the model and that measured by experiments

is presented in Fig. 6. It can be observed that the final

distribution is non-linear in space although the initial dis-

tribution is linear. The non-linearity is probably caused by

the migration of ions in the pore fluid resulting in a dif-

ferent distribution of electrical conductivity in the speci-

men. It can also be observed that the simulations and the

experimental measurements are in good agreement indi-

cating the validity of the theoretical formulation of the

phenomenon.

4.4 Enhancement of electrokinetic extraction

It can be observed in this study that the efficiency of

electrokinetic extraction of heavy metal contaminants can

be enhanced by solubilization of the contaminants. As the

transformation of most heavy metals is pH dependent,

keeping the soil at low pH appears to be a plausible solu-

tion. Techniques being investigated include simultaneous

injection of enhancement agents, such as purging solutions

(synthetic or natural), chelating agents, and complexing

agents including sulfuric acid, citric acid (Eykholt and

Daniel 1994; Gu et al. 2009b), EDTA (Yeung et al. 1996),

iodine/iodide lixiviant (Cox et al. 1996; Reddy et al. 2003),

humic acid, sodium acetate solution, nitric acid, to trans-

form the contaminants to their mobile phases so that they

can be effectively removed; acetic acid depolarization of

the cathode reaction, and use of ion-selective membrane to

veil hydroxide ions back-transport at the cathode (Rødsand

et al. 1995); and conditioning of electrodes and reservoir

solutions to specific pH to eliminate the adverse impacts of

electrode reactions (Lee and Yang 2000). More research on

these physicochemical soil-contaminant interactions is

certainly needed to develop better enhancement techniques

for electrokinetic extraction (Yeung 2009b).

Many new developments to enhance the technology

have been accomplished in recent years (Yeung 2006a).

These technologies include coupling of electrokinetic

extraction with a Fenton-like treatment process using a

permeable reactive wall of scrap iron powder to remove

and oxidize organic contaminants; modification of the

existing NEOCHIM technology for application in electro-

kinetic extraction (Leinz et al. 1998); use of the concept of

Integrated In situ Remediation to develop the Lasagna

process in which a dc electric field is applied to mobilize

contaminants from the contaminated soils into treatment

zones where the contaminants are removed by adsorption,

immobilization, or degradation (Ho et al. 1999a, b);

Fig. 4 Final pH distributions in Georgia kaolinite and Milwhite

kaolinite after 120 and 96 h of electrokinetic treatment, respectively

Fig. 5 Final total lead distributions in Georgia kaolinite and

Milwhite kaolinite after 120 and 96 h of electrokinetic treatment,

respectively

Fig. 6 Final voltage distributions in Georgia kaolinite and Milwhite

kaolinite after 120 and 96 h of electrokinetic treatment, respectively

36 Environmentalist (2011) 31:33–38

123

injection of bioremediation cometabolite or specific bac-

teria to engineer the degradation of recalcitrant hydrocar-

bons, or other difficult to degrade contaminants;

development of Ek-phytoremediation process as a combi-

nation of electrokinetic remediation and phytoremediation

to decontaminate soils contaminated by heavy metals.

5 Conclusions

Electrokinetic extraction technique has the potential in

mobilizing/removing heavy metal contaminants sorbed

onto soil particle surfaces. However, it can only transport

the contaminants in the liquid phase. The chemistry and

physicochemical soil-contaminant interactions associated

with the process are very complex. This study is conducted

to investigate these aspects by numerical modeling and

experimental studies on two different kaolinites. The

results of the study indicate that the acid/base buffer

capacity and the sorption–desorption characteristics of the

soil have profound impact on the contaminant removal

efficiency of the technique. The technique does not appear

to be feasible in soils of high acid/base buffer capacity

without proper enhancement. A numerical model has been

developed to simulate the process. The good agreement

between simulations and experimental measurements

indicates that the modeling approach is plausible and the

assumptions made are reasonable. Different enhancement

techniques have also been discussed. However, their fea-

sibility is still under investigation.

References

Acar YB, Gale RJ, Putnam GA, Hamed J, Wong RL (1990)

Electrochemical processing of soils: Theory of pH gradient

development by diffusion, migration, and linear convection.

J Environ Sci Health Part A—Environ Sci Eng Toxic Hazard

Subst Control 25(6):687–714

Acar YB, Li H, Gale RJ (1992) Phenol removal from kaolinite by

electrokinetics. ASCE J Geotech Eng 118(11):1837–1852

Banerjee S, Horng JI, Ferguson JF (1991) Field experience with

electrokinetics at a superfund site. In: Energy and environmental

issues. Transp Res Rec 1312, Transp Res Board, Washington,

DC, pp 167–174

Bruell CJ, Segall BA, Walsh MT (1992) Electroosmotic removal of

gasoline hydrocarbons and TCE from clay. ASCE J Environ Eng

118(1):68–83

Cox CD, Shoesmith MA, Ghosh MM (1996) Electrokinetic remedi-

ation of mercury-contaminated soils using iodine/iodide lixivi-

ant. Environ Sci Technol 30(6):1933–1938

Ellis WD, Fogg TR, Tafuri AN (1986) Treatment of soils contam-

inated with metals. In: Proceedings of 12th Annual Research

Symposium: Land disposal, remedial action, incineration and

treatment of hazardous waste, Report no. EPA/600/S9-86/022,

US EPA, Cincinnati, pp 201–207

Eykholt GR, Daniel DE (1994) Impact of system chemistry on

electroosmosis in contaminated soil. ASCE J Geotech Eng

120(5):797–815

Gopinath S (1994) A laboratory study of electro-kinetic remediation

of fine-grained soil contaminated with organic compounds. MS

Thesis, Texas A&M University

Gu Y-Y, Yeung AT, Li H-J (2009a) EDTA-enhanced electrokinetic

extraction of cadmium from a natural clay of high buffer

capacity. In: Proceedings of International Symposium on

Geoenvironmental Engineering (ISGE 2009), Hangzhou,

pp 790–795

Gu Y-Y, Yeung AT, Koenig A, Li H (2009b) Effects of chelating

agents on the zeta potential of cadmium-contaminated natural

clay. Sep Sci Technol 44(10):2203–2222

Hamed J, Acar YB, Gale RJ (1991) Pb(II) removal from kaolinite

using electrokinetics. ASCE J Geotech Eng 117(2):241–271

Ho SV, Athmer C, Sheridan PW, Hughes BM, Orth R, Mckenzie D,

Brodsky PH, Shapiro A, Thornton R, Salvo J, Schultz D, Landis

R, Griffith R, Shoemaker S (1999a) The Lasagna technology for

in situ soil remediation. 1. Small field test. Environ Sci Technol

33(7):1086–1091

Ho SV, Athmer C, Sheridan PW, Hughes BM, Orth R, Mckenzie D,

Brodsky PH, Shapiro AM, Sivavec TM, Salvo J, Schultz D,

Landis R, Griffith R, Shoemaker S (1999b) The Lasagna

technology for in situ soil remediation. 2. Large field test.

Environ Sci Technol 33(7):1092–1099

Lageman R, Godschalk MS (2007) Electro-bioreclamation—A com-

bination of in situ remediation techniques proves successful at a

site in Zeist, the Netherlands. Electrochim Acta 52(10):3449–

3453

Lageman R, Clarke RL, Pool W (2005) Electro-reclamation, a

versatile soil remediation solution. Eng Geol 77(3–4):191–201

Lee HH, Yang JW (2000) A new method to control electrolytes pH by

circulation system in electrokinetic soil remediation. J Hazard

Mater 77(1–3):227–240

Leinz RW, Hoover DB, Meier AL (1998) NEOCHIM: an electro-

chemical method for environmental application. J Geochem

Explor 64(1–3):421–434

Maini G, Sharman AK, Knowles CJ, Sunderland G, Jackman SA

(2000) Electrokinetic remediation of metals and organics from

historically contaminated soil. J Chem Technol Biotechnol

75(8):657–664

Menon RM (1996) Numerical modeling and experimental study on

electro-kinetic extraction. Dissertation, Texas A&M University

Pamukcu S, Wittle JK (1992) Electrokinetic removal of selected

heavy metals from soil. AIChE Environ Prog 11(3):241–250

Probstein RF, Hicks RE (1993) Removal of contaminants from soils

by electric fields. Sci 260(5107):498–503

Reddy KR, Chaparro C, Saichek RE (2003) Iodide-enhanced

electrokinetic remediation of mercury-contaminated soils. ASCE

J Environ Eng 129(12):1137–1148

Rødsand T, Acar YB, Breedveld G (1995) Electrokinetic extraction of

lead from spiked Norwegian marine clay. In: Acar YB, Daniel

DE (eds) Characterization, containment, remediation, and per-

formance in environmental geotechnics. Geotech Spec Publ No

46, vol 2. ASCE, New York, pp 1518–1534

Sawada A, Tanaka S, Fukushima M, Tatsumi K (2003) Electrokinetic

remediation of clayey soils containing copper(II)-oxinate using

humic acid as a surfactant. J Hazard Mater 96(2–3):145–154

Shapiro AP, Probstein RF (1993) Removal of contaminants from

saturated clay by electroosmosis. Environ Sci Technol 27(2):

283–291

Suer P, Allard B (2003) Mercury transport and speciation during

electrokinetic soil remediation. Water Air Soil Pollut 143(1–4):

99–109

Environmentalist (2011) 31:33–38 37

123

van Olphen H (1977) An introduction to clay colloid chemistry, 2nd

edn. Wiley, New York

van Olphen H, Fripiat JJ (eds) (1979) Data summaries—Clay

minerals society. In: Data handbook for clay materials and other

non-metallic minerals. Pergamon Press, New York, pp 13–37

Yang GCC, Long Y-W (1999) Removal and degradation of phenol in

a saturated flow by in situ electrokinetic remediation and Fenton-

like process. J Hazard Mater 69(3):259–271

Yeung AT (1992) Diffuse double-layer equations in SI units. ASCE J

Geotech Eng 118(12):2000–2005

Yeung AT (1994) Electrokinetic flow processes in porous media and

their applications. In: Corapcioglu MY (ed) Advances in porous

media, vol 2. Elsevier, Amsterdam, pp 309–395

Yeung AT (2006a) Contaminant extractability by electrokinetics.

Environ Eng Sci 23(1):202–224

Yeung AT (2006b) Fundamental aspects of prolonged electrokinetic

flows in kaolinites. Geomech and Geoeng: An Int J 1(1):13–25

Yeung AT (2008) Electrokinetics for soil remediation. In: Yeung AT,

Lo IMC (eds) Environmental geotechnology and global sustain-

able development 2008. Advanced Technovation Ltd, Hong

Kong, pp 16–25

Yeung AT (2009a) Remediation technologies for contaminated sites.

In: Proceedings of the International Symposium on Geoenvi-

ronmental Engineering (ISGE 2009), Hangzhou, pp 328–369

Yeung AT (2009b) Geochemical processes affecting electrochemical

remediation. In: Reddy K, Cameselle C (eds) Electrochemical

remediation technologies for polluted soils, sediments and

groundwater. Wiley, New York, pp 65–94

Yeung AT, Datla S (1995) Fundamental formulation of electrokinetic

extraction of contaminants from soil. Can Geotech J 32(4):569–

583

Yeung AT, Hsu C (2005) Electrokinetic remediation of cadmium-

contaminated clay. ASCE J Environ Eng 131(2):298–304

Yeung AT, Hsu C, Menon RM (1996) EDTA-enhanced electrokinetic

extraction of lead. ASCE J Geotech Eng 122(8):666–673

Yeung AT, Hsu C, Menon RM (1997a) Physicochemical soil-

contaminant interactions during electrokinetic extraction. J Haz-

ard Mater 55(1–3):221–237

Yeung AT, Scott TB, Gopinath S, Menon RM, Hsu C (1997b) Design,

fabrication, and assembly of an apparatus for electrokinetic

remediation studies. ASTM Geotech Test J 20(2):199–210

38 Environmentalist (2011) 31:33–38

123