lead removal from contaminated marine clay by electrokinetic soil decontamination

Engineering Geology 53 (1999) 139–150

Lead removal from contaminated marine clay byelectrokinetic soil decontamination

H.I. Chung a,*, B.H. Kang ba Geotechnical Engineering Division, Korea Institute of Construction Technology, 2311 Taewhadong Ilsanku Koyang,

Kyonggido, South Koreab Department of Civil Engineering, Inha University, 253 Yonghyundong Namku, Incheon, South Korea

Abstract

This paper reports the remediation of marine clay contaminated with lead by electrokinetics. A series ofelectrokinetic decontamination experiments including variable conditions such as operating duration, electrical current,concentration of lead and applications of three different chemicals were performed to demonstrate the efficiency oflead removal from natural marine clay sampled in Korea. The experiment results showed that the amounts ofhydrogen ions and electroosmotic water flow transported from anode to cathode increased with increasing in theoperating duration and the applied electrical current, and with decreasing the initial concentration of lead. Theefficiency of heavy metal removal from the contaminated soil was increased with increasing in the operating duration,the applied electrical current and the initial lead concentration. The chemicals used as deprecipitating, complexingand solubilizing agents were efficient in removal of lead from the soil. Here arises a suggestion that injection of suchchemicals could be effective in removal of heavy metals from the soil as an auxiliary method in electrokineticdecontamination. © 1999 Elsevier Science B.V. All rights reserved.

Keywords: Contaminated clay; Electrokinetics; Lead; Remediation

1. Introduction strata, and diversion schemes of a contaminantplumes in civil and environmental engineering(Acar et al., 1990, 1993; Acar and Alshawabkeh,Electrokinetics is the movement of water, ions1993; Mitchell, 1991; Ugaz et al., 1992; Yeung,and charged solid particles between two electrodes1994). Electrokinetic decontamination can removeunder the influence of an electrical field.heavy metals and organic pollutants from clayeyElectrokinetics can be applied to the fields such assoils, sludges and sediments.consolidation and stabilization of soft soil and

In Korea, the industry is commonly locatedsludge, stabilization of slopes, dewatering in con-near the seashore, therefore some marine depositsstruction sites, decontamination of pollutants, bar-at the seashore are potentially contaminated. Thererier system in clay liners, sealing and leak-detectionis a Korean criterion of soil contamination forsystem of geomembrane, injection of chemical,cadmium, copper, arsenic, mercury, lead,microorganisms as well as nutrients into subsoilchromium6+, organophosphorus compound, poly-chlorinated biphenyl, cyanogen, phenol and oilcompound (Ministry of Environment, 1996). For* Corresponding author.

E-mail address: [email protected] (H.I. Chung) example, a lead contamination of 300 mg kg−1 at

0013-7952/99/$ – see front matter © 1999 Elsevier Science B.V. All rights reserved.PII: S0013-7952 ( 99 ) 00027-7

140 H.I. Chung, B.H. Kang / Engineering Geology 53 (1999) 139–150

farm land and 1,000 mg kg−1 at a factory or such as clay. Fig. 1 shows a schematic representa-tion of the electrokinetic transport of water byindustrial sites indicate that an action needs to be

taken to clean up or dispose of the soil. electroosmosis and charged species such as heavymetal ions by electromigration in soils. These twoThis paper presents a study on an electrokinetic

decontamination for removal of lead from contam- mechanisms, electroosmosis and electromigration,are the primary driving forces to extract contami-inated marine clay spiked with lead. For this

purpose, a series of laboratory experiments includ- nants from the electrokinetic remediation process-ing (Acar et al., 1990; Alshawabkeh and Acar,ing variable conditions such as operating duration,

applied electrical current, concentration of lead, 1992; Yeung et al., 1997). Numerous electrochemi-cal reactions and soil contaminant interactions,and applications of three different chemicals, were

performed. Investigated are pH values of catholyte such as electrolysis, sorption and desorption ofcontaminants onto and from a clay particle sur-and anolyte, volume of water extracted from the

soil specimen, the changes in pH and electrical face, acidification of soil by the transport of thehydrogen ion, precipitation of inorganic species,conductivity of the contaminated soils, distribution

of electrical potential in the soil between the two occur simultaneously (Acar et al., 1993; Røsandand Acar, 1996; Yeung et al, 1997).electrodes. The efficiency of lead removal by the

proposed method was evaluated under various When an electrical charge is supplied to thesaturated soils, an electrolysis reaction of wateroperating conditions including the use of three

chemicals. takes place. Oxygen and hydrogen ions are pro-duced at the anode and hydrogen and hydroxideions are produced at the cathode. The water elec-trolysis reactions are defined by the following2. Backgroundreactions:

Electroosmotic technologies have been in useAnode: 2H2O−4e−�O

2(+4H+ (1)since the 1930s in construction sites, such as dewa-

tering and slope stabilization. A railway cut was Cathode: 4H2O+4e−�2H2(+4OH− . (2)

stabilized in 1930 and a German U-boat site wasdewatered in 1943. Segall et al. (1980) reported This causes reduction of pH at the anode compart-

ment, and increase of pH at the cathode compart-electroosmotic liquid contained high concen-trations of metals, organics and total dissolved ment. Subsequently the hydrogen ions migrate

towards the cathode by electroosmosis andsolids. Electroosmotic technology as a potential insitu remediation technique for contaminated soils electromigration, on the other hand the hydroxide

ions migrate towards the anode by electromigra-was promoted by this discovery. From the late1980s, interest in electrokinetic technology for tion. The ionic mobility of hydrogen ions is nearly

twice as high as that of the hydroxide ions. Theremediation has increased. A study on the electro-kinetic remediation has been conducted by several soil is then acidified with further electrokinetic

processing. Such acidification of the soil would beuniversities, public and private institutes and com-panies, such as Louisiana State University, effective in removal of metals adsorbed and precip-

itated in the soil, because hydrogen ions will tendUniversity of Texas A&M, MIT, Lehigh Universityand Electro-Petroleum Inc. in the USA, to exchange with metal ions adsorbed to clay

particles, and the low pH condition is favourableGeokinetics in The Netherlands and LeedsUniversity and University of Cambridge in the for the dissolution of most metal precipitates.

Electroosmosis is the movement of a liquidUK (Acar et al., 1990, 1993; Yeung, 1994; Reedet al., 1995; West and Stewart, 1996; Penn and under the applied electric potential. The most

widely accepted theory is that net water flowSavvidou, 1996).Electrokinetic remediation is an emerging in resulted when momentum transfer between migrat-

ing ions of one sign and the surrounding watersitu technology developed to extract organic andinorganic contaminants from fine grained soils molecules exceeds that of the ions of the opposite

141H.I. Chung, B.H. Kang / Engineering Geology 53 (1999) 139–150

Fig. 1. Schematic representation of an electrokinetic decontamination process in soil.

sign. It is thought that water surrounding the ions port ionic and nonionic species through soiltowards the cathode compartment. This is perhapsis dragged along a via frictional forces. Since most

soils have a negative surface charge, there are more best achieved when the state of materials dissolved,suspended, emulsified, etc. are suitable for thecations than anions in electrical double layers, so

net flow of water will be towards the cathode. flowing water to carry them through the soil pore.When a DC current is applied to a soil system,Electroosmotic flow was modelled by the

Helmholz–Smoluchowski theory as follows: cations move towards the negatively charged cath-ode and anions move towards the positivelycharged anodes. Electromigration of ions is per-qe=ke ieA=kiI=

kis

I, (3)haps the major cause of conduction of currentthrough a porous medium containing a moderatelywhere qe is the electroosmotic flow rateconcentrated aqueous solution of electrolytes. Acar(cm3 s−1); ke is the coefficient of electroosmoticet al. (1993) have reported that the migrationalpermeability (cm2 V−1 s−1); ie is the potential gra-mass flux of ions can be represented by thedient (V cm−1); A is the cross-sectional areafollowing equation:(cm2); ki is the coefficient of the water transport

efficiency (cm3 A−1 s−1); I is the current (A); ando1=

D1zF

RT, (4)s is the conductivity of the material (S cm−1). The

velocity of electroosmosis water flow provided byHelmholz–Smoluchowski is described in Fig. 1 where D1 is the effective diffusion coefficient

(cm2 s−1); z is the valence of the ion; F is the(Hamed et al., 1991). Electroosmosis produces arapid flow of water in low permeability soils and Faraday constant; R is the universal gas constant;

and T is the absolute temperature.electroosmotic advection should be able to trans-


3. Electrokinetic experiments Pb(NO3)2 and deionized water (Chung et al., 1995;Jeong and Kang, 1997).

3.1. Materials3.2. Testing programs

Marine clay was sampled at Kimpo reclaimedland in the west seashore of Korea. Table 1 con- A schematic diagram of the electrokinetic

decontamination system is shown in Fig. 2. Thistains the physical and chemical properties of thismarine clay used in this experiment. The index system mainly consisted of electrokinetic cell, ano-

lyte and catholyte reservoir, and power supply.properties of this soil were specific gravity 2.58,plasticity index 10.3%, percent finer than #200 The electrokinetic cell was a cylindrical tube with

100 mm in length and 100 mm in diameter. Thesieve 90%, and coefficient of permeability2×10−7 cm/s. The compaction properties were end reservoir solutions were circulated constantly

by pump to check the anolyte and catholyte pH.maximum dry density 1.73 g cm−3 and optimumwater content 18.2%. The chemical properties were Graphite electrodes were used to prevent pro-

duction of corrosion and two sheets of filter papersorganic matter content 6.74%, initial pH 6.5–7.13,and initial electrical conductivity 1500 ms cm−1. were placed at both ends of the specimen to

stabilize the soil specimen. Two electrodes wereThe chemical constituent was as follows: SiO269.20%, Al2O3 13.97%, Fe2O3 4.30%, etc. The soil not in direct contact with the soil. To allow venting

of gas produced by electrolysis, holes were drilledsample was artificially contaminated with leadusing an aqueous lead solution. Lead solutions into the top of each end reservoir.

In this paper, 12 tests were conducted by usingwere obtained by stock solution prepared withone-dimensional electrokinetic test apparatus forlead removal without and with any enhancement.

Table 1Parameters such as operating duration, currentPhysical and chemical properties of the test soilsdensity, concentration of lead, and enhancement

Items Values methods were chosen in these experiments.Constant current conditions were used in all tests

Specific gravity 2.58to minimize complicated electrical boundary con-Atterberg limits (%)ditions and to keep the net rates of the electrolysisLiquid limit 32.8

Plastic limit 22.5 reactions constant at all testing times (HamedPlasticity index 10.3 et al., 1991). The testing program is summarised

Percent finer than No. 200 sieve 90.0 in Table 2.Specific surface area (cm2 g−1) 5249

Three different chemicals like nitric acid as aCoefficient of uniformity 4.5deprecipitating agent, ethylenediamine as a com-Activity 0.114

Proctor compaction parameter plexing agent and acetic acid as a solubilizingMaximum dry density (g cm−3) 1.73 agent were used for the enhanced electrokineticOptimum water content (%) 18.2 test (Pamukcu and Wittle, 1994; Røsand and Acar,

Hydraulic conductivity (cm s−1) 2×10−71996; Chung, 1996). A few drops of pure nitricOrganic matter content (%) 6.74acid were put into lead solution to reduce leadpH 6.5–7.13

Electrical conductivity (ms cm−1) 1500 precipitation in soils. Ethylenediamine was injectedChemical constituents (%) into the anode chamber of a lead contaminated

SiO2 69.20 soil specimen and it penetrated the soil specimenAl2O3 13.97

by electroosmotic flow. The amount of ethylenedi-Fe2O3 4.30amine injected was a 10:1 ratio of moles of ethylen-CaO 0.95

MgO 1.61 ediamine:lead in soil to ensure complexation of allK2O 2.41 the lead available. Acetic acid (0.01 M) was intro-Na2O 2.17 duced at the cathode chamber to depolarized theTiO2 1.35

cathode reaction.


Fig. 2. A schematic of the electrokinetic apparatus.

3.3. Testing procedure specimen was circa 2×10−7 cm s−1. The cell wasassembled to the electrokinetic test system.

A constant current was applied to the cells andKimpo marine clay was dried, crushed, pulver-ized and mixed with the lead solution. The mixture the voltage was measured on a daily basis. pH

measurement was made in the anode and cathodewas cured in a bowl for longer than 24 h. Themixture spiked with lead was compacted in an reservoir. The time dependant water movement

through the soil due to electroosmosis was mea-electrokinetic cell. Each clay sample that was pre-pared, the water content was optimum moisture sured on the outflow by graduated cylinder. After

an electrokinetic test, the cell was disassembledcontent, the dry density was 95% of the maximumdry density. The hydraulic conductivity of the from the electrokinetic system and the soil speci-

Table 2Summary of testing program

Test Initial concentration Operating duration Applied electrical Enhancementnumber of Pb (mg kg−1) (days) current (mA) method

1 0 15 50 –2 500 15 50 –3 5000 15 50 –4 50 000 15 50 –5 5000 5 50 –6 5000 30 50 –7 5000 15 10 –8 5000 15 30 –9 5000 15 100 –10 5000 15 50 Deprecipitation11 5000 15 50 Complexation12 5000 15 50 Solubilization


men was extruded and sliced into ten sections. Thevalue of pH and the concentration of lead weremeasured in each slice to assess the change in thechemical properties in the soil specimen and theefficiency of the process in lead removal.

4. Results and discussion

4.1. Anolyte and catholyte pH

Plots of anolyte (inflow) and catholyte (outflow)pH for tests with different electrical currents at anoperating duration of 15 days and a contaminationlevel of 5000 mg kg−1 are shown in Fig. 3. Fig. 4. The change in anolyte and catholyte pH by different

The anolyte pH was measured at the inflow contamination levels.reservoir and catholyte pH was measured at theoutflow reservoir during an electrokinetic decon-tamination test. The anolyte pH dropped to values dropped to values of 2–3 and the pH of the

cathode reservoir rose to values of 11–13 upon theof 2–3 and the catholyte pH rose to a value of11–13 upon the start of the electrokinetic test start of the electrokinetic test. And then the pH

remained relatively constant. In all the tests forregardless of the different electrical currents.Subsequently, the pH remained relatively constant different operating durations, electrical currents,

contamination levels and enhancement methodswith further processing. This results from theelectrolysis of water. Therefore, the generation of except ethylenediamine injection, the anolyte pH

decreased and the catholyte pH increased on theoxygen gas and hydrogen ion at the anode loweredthe pH, and generation of hydrogen gas and start of current application regardless of the oper-

ating times, applied currents and concentrationhydroxide ion at the cathode increased the pH.The change in the anolyte and the catholyte pH levels.

during electrokinetic tests for different contamina-tion levels at current of 50 mA and operating 4.2. Soil pHduration of 15 days is presented in Fig. 4. Also,this figure shows that the pH of anode reservoir The profiles of pH across the soil specimen by

different operating durations at current of 50 mAand a contamination level of 5000 mg kg−1 areshown in Fig. 5. This demonstrates that the acidfront generated at the anode advances steadilytowards the cathode, while the base front generatedat the cathode remains in the cathode. The acidfront progressed to the cathode by advection,migration and diffusion and neutralized the baseof the cathode. The transient acid front movementin soil was beneficial for metal desorption anddissolution, which in turn contributed to theremoval process. The fronts met at a normalizeddistance of circa 0.6 from the anode after 5 days,circa 0.8 after 15 days, and above 1.0 after 30 days.Fig. 3. The change in anolyte and catholyte pH by different

electrical currents. The plots of the soil pH across the contaminated


higher concentrations, the electroosmotic flow wassmall, thus transport was mainly by electomigra-tion. Where the contamination levels was up to5000 mg kg−1 the acid front and base front met ata normalized distance of circa 0.8 from the anode.On the other hand, where the contamination levelwas 50 000 mg kg−1, the acid front and base frontmet at a normalized distance of circa 0.5 fromthe anode.

The final pH value across the soil specimendecreased in the enhancement tests such as intro-ducing nitric acid in the soil specimen and acetic

Fig. 5. Final pH distribution across the soil specimen by acid in the cathode compartment, due to acidifica-different operating times.

tion of the soil specimen by applied nitric acid andacetic acid. In the test of ethylenediamine injection,

specimen for tests with different electrical currents the soil pH remained between 6 and 10 for theat 15 days of processing and 5000 mg kg−1 of entire length of the soil specimens. From the abovecontamination level are shown in Fig. 6. The fronts test results, we can recognize that the quantities ofmet at a normalized distance of circa 0.65 from hydrogen ions transported from the anode to thethe anode at a current of 10 mA, circa 0.78 at a cathode increased with an increase in the operatingcurrent of 50 mA, and circa 0.85 at a current of duration and the applied electrical current, and a100 mA. The final distributions of the pH value decrease in the initial concentration of lead.across the soil specimen decreased with an increasein the operating time and applied current, because 4.3. Electrical potential gradientstransport of the acid generated at the anodeincreased with an increase in the duration and The variation of electrical potential across thecurrent. soil specimen for tests with different electrical

The final pH value across the soil specimens currents applied during electrokinetic tests at oper-increased with an increase in the concentration of ating duration of 15 days and a contaminationlead. That reason might be the superposition of level of 5000 mg kg−1 is presented typically inelectroosmotic flow on electromigration (West and Fig. 7. The final electrical potentials by electricalStewart, 1996). At lower concentrations, the currents from this figure were 2.1 V cm−1 at aelectroosmotic flow was large, thus transport was current of 10 mA, 11.3 V cm−1 in the current ofby electroosmosis and electomigration. But at

Fig. 7. Increments of electrical potential with time by appliedFig. 6. Final pH distribution across the soil specimen bydifferent electrical currents. electrical currents.


50 mA, and 18.0 V cm−1 in the current of 100 mAafter 360 h, due to variations in the current density.This result shows that the electrical potentialdifferences across the electrodes increased with anincrease in the applied current.

The final electrical potentials with differentoperating durations were 0.5 V cm−1 by 120 h,5.0 V cm−1 by 240 h, 11.3 V cm−1 by 360 h and13.4 V cm−1 by 720 h, due to an increase in theresistance in the soil specimen with elapsed time.The final electrical potentials with concentrationof lead after 360 h were 13.1, 12.0, 11.3,2.5 V cm−1 at concentrations of 0, 500, 5000, Fig. 8. Variation of electroosmotic flow by different electrical50 000 mg kg−1 each due to the charge transport currents.capacity. The final electrical potentials withenhancement method after 360 h were 11.3 Vcm−1 in unenhanced conditions, 10.5 V cm−1 in demonstrate that the electroosmotic flow increased

with an increase in the current. The accumulatedthe enhanced condition of nitric acid, 7.0 V cm−1in the enhanced condition of ethylenediamine, and quantity of flow after 360 h was 20, 120 and 670 ml

in 10, 50 and 100 mA current each due to varia-5.0 V cm−1 in the enhanced condition of aceticacid, since lowering the pH across the specimen tions in the density of applied electrical current.

In a high current application, the electroosmoticfor enhanced tests would decrease the overallresistance in the soil. flow towards the cathode began almost immedi-

ately upon current application. But in the lowHere arises the fact that the electrical potentialdifferences across the electrodes increased with an current application, the electroosmotic flow began

a little later in accordance with the magnitude ofincrease in the operating duration and appliedcurrent, and decreased with an increase in the applied current.

In the tests of the different operating durations,concentration of lead, also decreased with an intro-duction of nitric acid, acetic acid and ethylenedi- the electroosmotic water flow at the cathode

increased with an increase in the operating dura-amine in the soil specimen. The increase of electri-cal potential in the tests for the different operating tion. There was no measurable flow within the first

40 h of the current application. Subsequently, theduration and electrical current is probably associ-ated with the formation of a lead hydroxide, which flow increased rapidly up to 115 ml by 300 h and

then increased slowly up to 130 ml by 720 h. Inreduces ionic strength and soil pore space. Thedecrease in electrical potential in the tests of the cases of the enhancement tests, the electroos-

motic flow increased in the enhanced case com-different contamination levels is probably relatedwith transport capacity of electrical charge due to pared with the unenhanced cases. The enhanced

test introduced acetic acid at the cathode reservoirthe difference in ionic concentration existing inthe soil. exhibited highest electroosmotic flow of 400 ml

after 15 days, whereas unenhanced electrokinetictest exhibited lowest flow of 120 ml after 15 days.4.4. Electroosmotic flow

In Fig. 9, a plot of electroosmotic flow withconcentration levels at the end of 360 h at anThe electroosmotic flow was directed towards

the cathode from the anode in all tests. An example application of 50 mA are shown. The total flowvolume was circa 420 ml at a concentration ofof the electroosmotic flow over the different electri-

cal current applied in an electrokinetic tests with zero, 390 ml at a concentration of 500 mg kg−1,120 ml at a concentration of 5000 mg kg−1 and15 days duration and a 5000 mg kg−1 concen-

tration level is presented in Fig. 8. These results 25 ml at a concentration of 50 000 mg kg−1. The


Fig. 10. Distribution of final lead concentration across the soilFig. 9. Variation of electroosmotic flow by different contamina-specimen by different operating durations.tion levels.

quantities of flow through uncontaminated and the average removal rate of lead in the soil speci-men was 13% after 5 days, 88% after 15 days andcontaminated samples with concentrations of

500 mg kg−1 were similar, whereas contaminated 95% after 30 days. Any removal of the adsorbedlead should involve its desorption into the poresamples with 50 000 mg kg−1 were less. These

results could be explained by the zeta potential fluid by cation exchange of the hydrogen ionsadvancing across the soil specimen and its subse-(West and Stewart, 1996). At a concentration level

of 500 mg kg−1 or less, the zeta potential was more quent flushing to the cathode by transport andadvection. For the soil specimens where the remedi-negative. On the other hand at a concentration

level of 50 000 mg kg−1, the zeta potential was less ation process was operated for a relatively shortperiod, the lead was completely removed from thenegative. Thus the electroosmotic flow propor-

tioned directly to zeta potential is reduced with section near the anode, but accumulated to someextent near the cathode. On the other hand wherehigher concentration. Flow rate began to rapidly

reduce after circa 170 h for the tests with concen- the remediation process was executed for a longperiod, the lead was evenly removed throughouttrations level of 5 000 and 50 000 mg kg−1, on the

other hand the flow rate began to slightly decrease the soil specimen.The normalized lead concentration profiles withafter circa 300–350 h for the tests with contamin-

ation levels up to 500 mg kg−1. different electrical currents at the operating dura-tion of 15 days and contamination level of5000 mg kg−1 are plotted in Fig. 11. The test4.5. Efficiency of lead removalresults shows that the efficiency of extracting leadfrom a soil specimen increased with an increase inThe normalized lead concentration ratio across

the soil specimens determined at the conclusion of the applied currents. The average concentrationratio of lead was 0.65 in the current of 10 mA,the electrokinetic experiments for tests with 5, 15,

30 days operating times at an electrical current 0.12 in the current of 50 mA, and 0.06 in thecurrent of 100 mA. Thus, the average removal rateof 50 mA and a contamination level of

5000 mg kg−1 are presented as a function of nor- of lead was 35, 88 and 94% in the current of 10,50 and 100 mA. When an electrical field of lowmalized distance from the anode in Fig.10. This

figure shows that lead was progressively advanced currents was applied to the soil specimens in theelectrokinetic remediation tests, the lead was com-from the anode to the cathode as time elapsed.

The average concentration ratio of lead in an pletely removed from the anode compartment, butaccumulated to some extent near the cathodeentire specimen was 0.87 after 5 days, 0.12 after

15 days and 0.05 after 30 days. This means that compartment. But when high currents were


The injection of three chemicals into the soilspecimen contaminated with lead was tried toenhance the electrokinetic decontamination. Allenhancement of experiments presented significantlead transport and removal through the soil speci-men. The chemicals such as nitric acid, ethylenedi-amine and acetic acid used as deprecipitating,complexing and solubilizing agents were efficientin removal of lead from the soil. But the removalefficiency would be variable with the concentrationand the quantity of chemical agents applied in theelectrokinetic test. The lead removal efficiency ofabove 88% was achieved in all enhancement experi-Fig. 11. Distribution of final lead concentration across the soilments conducted in this study. This would resultspecimen by different electrical currents.in a prevention of hydroxide precipitation andsolubilization of the species in transport and itapplied, the lead was evenly removed across thewould be rendered efficient removal of speciesentire soil specimen.(Røsand and Acar, 1996; Pamukcu and Wittle,The final concentration profiles of lead in the1994; Cline and Reed, 1995). Chelants such assoil specimens with different concentration levelsethylenediamine can readily form soluble com-after 15 days of test duration at an electrical cur-plexes with a lead ion, reducing the quantity ofrent of 50 mA are plotted in Fig. 12. It is notedmetals retained by soil particles, thereby increasingthat the efficiency of the lead extraction was highestheavy metal mobility, and easily removing metalsin the highest contaminated soil and lowest in thebound by soils. The pH control inside and bothleast contaminated soil. At low levels of concen-ends of soil specimen should create suitable envi-tration, the transport of lead was slower becauseronments for the metal ions to remain in solutionalmost all the lead was adsorbed to the soil particleof the pore, so that they can be extracted in aand required a replacement by other cations suchfeasible manner. Acetic acid can decrease the pHas hydrogen ion H+. But at high levels of concen-value, depolarize the cathode reaction, and solubi-tration, the transport of lead was faster becauselize the hydroxide precipitation on the cathode.most of the leads were free in the pore and notThe acetic acid enhancement method produced aadsorbed to the soil particle, thus relatively easilybest removal efficiency of 94% in enhancementand quickly moved to the cathode on currentmethod. This could suggest that the injection ofapplication.such chemicals could be effective in removal ofheavy metals from the soil as an auxiliary methodin electrokinetic decontamination.

In this study, the clay sample contained circa7% of organic material. Therefore, the complex-ation could be expected between the lead ion andorganic substance as suggested by Yonget al.(1992), because the organic components ofthe soil constituents has a high affinity for heavymetal cation. This leads to the conclusion that thecomplexation phenomenon should affect the trans-portation and remediation of the lead ion. Fromthe electrokinetic test results mentioned above, theefficiency of lead removal from the contaminatedFig. 12. Distribution of final lead concentration across the soil

specimen by different contamination levels. soil was increased by increasing the operating time,


the applied electrical current and the initial lead used as deprecipitating, complexing, and solubiliz-ing agents were found to be efficient in removingconcentration, and with the application of the

enhancement method. lead from the soil. The addition of the selectedchemicals into the contaminated soil expedited theremediation process. Here arises a suggestion thatthe injection of such chemicals could be effective5. Conclusionsin removing heavy metals from the marine clay asan auxiliary method in electrokineticLaboratory bench scale experiments demon-

strated the removal efficiency of lead from contam- decontamination.inated natural marine clay. Electrokineticdecontamination can be used in the extraction ofheavy metals from high plastic marine clay. The

Referencestest results showed that the anolyte pH decreasedand the catholyte pH increased at the start of

Acar, Y.B., Alshawabkeh, A.N., 1993. Principles of electroki-current application regardless of the operatingnetic remediation. Environmental Science and Technology

time, the applied electrical currents and the concen- 27 (13), 2638–2647.tration levels. The pH across the soil specimen Acar, Y.B., Gale, R.J., Putnam, G.A., Hamed, J., Wong, R.L.,

1990. Electrochemical processing of soils: theory of pH gra-increased by increasing the operating time and thedient development by diffusion migration and linear convec-applied electrical current, and decreasing the initialtion. Journal of Environmental Science and Health A25concentration level of the lead. The transient acid(6), 687–714.

front movement in soil from the anode to cathode Acar, Y.B., Alshawabkeh, A.N., Gale, R.J., 1993. Fundamen-site was beneficial for metal desorption and dis- tals of extracting species from soils by electrokinetics. Waste

Management 13, 141–151.solution, which in turn contributed to the removalAlshawabkeh, A.N., Acar, Y.B., 1992. Removal of contami-process. Electroosmotic water flow transported

nants from soils by electrokinetics: A theoretical treatise.from anode to cathode increased with a decreaseJournal of Environmental Science and Health A27 (7),

in the initial concentration of lead and an increase 1835–1861.in the operating time and the applied electrical Chung, H., 1996. Removal of heavy metals from contaminated

ground by electrokinetic remediation. PhD Dissertation,current. There was no measurable electroosmoticInha University, South Korea.flow within the first 40 h of current application.

Chung, H., Lee, Y., Woo, J., 1995. A study on the remedialSubsequently, the flow increased rapidly by 300 htechnologies of contaminated soil and groundwater, Final

and then increased slowly. Research Report, KICT 95-GE-1101-2. Korea Institute ofIn the experiments of low currents and short Construction Technology, Korea, pp. 5–195.

Cline, S.R., Reed, B.E., 1995. Lead removal from soils viatimes, the lead was completely removed at thebench-scale soil washing techniques. Journal of Environ-anode section and accumulated near the cathodemental Engineering, ASCE 121 (10), 700–705.section. But in the high currents over long dura-

Hamed, J., Acar, Y.B., Gale, R.J., 1991. Pb (II ) removal fromtions, the lead was evenly removed throughout the kaolinite by electrokinetics. Journal of Geotechnical Engi-soil specimen. Two major transport processes such neering, ASCE 117 (2), 242–271.

Jeong, H., Kang, B., 1997. Removal of lead from contaminatedas transport by electroosmotic flow and electromi-Korean marine clay by electrokinetic remediation technol-gration of ions were involved in electrokineticogy, Geoenvironmental Engineering Contaminatedremediation. Electroosmosis and electromigrationGround: Fate of Pollutants and Remediation. Thomas Tel-

were superposed on decontamination of heavy ford, London, pp. 423–430.metals from low contaminated soils, but electromi- Ministry of Environment, 1996. A Handbook for Conservation

of Soil Environment, Korean Administrative Publicationgration was dominant in highly contaminated soils.No. 12000-67630-67-9613. Ministry of Environment,The extract efficiency of heavy metal from theKorea, pp. 1–54.contaminated soil was increased with an increase

Mitchell, J.K., 1991. Conduction phenomena: from theory toin the operating time, the applied electrical current geotechnical practice. Geotechnique 41 (3), 299–340.and the initial lead concentration. Chemicals such Pamukcu, S., Wittle, J.K., 1994. Electrokinetically enhanced in

situ soil decontamination, Remediation of Hazardous Wasteas nitric acid, ethylenediamine, and acetic acid


and Contaminated Soils. Marcel Dekker, New York, ries: saturation effects and the role of the cathodeelectrolysis. Paper presented at the AICHE 1992 Meeting inpp. 245–298.

Penn, M., Savvidou, C., 1996. Centrifuge modeling of the Florida. Department of Chemistry and Civil Engineering,Louisiana State University, LA.removal of heavy metal pollutants using electrokinetics,

Environmental Geotechnics vol. 2. Balkema, Rotterdam, West, L.J., Stewart, D.I., 1996. Effect of zeta potential on soilelectrokinetics. Geoenvironment 2000, 1535–1549.pp. 1055–1060.

Røsand, T., Acar, Y.B., 1996. Electrokinetic extraction of lead Yeung, A.T., 1994. Electrokinetic flow processes in porousmedia and their applications. In: Corapcioglu, M.Y. (Ed.),from spiked Norwegian marine clay. Geoenvironment 2000,

1518–1533. Advances in Porous Media vol. 2. Elsevier, Amsterdam,pp. 309–395.Reed, B.E., Berg, M.T., Thompson, J.C., Hatfield, J.H., 1995.

Chemical conditioning of electrode reservoirs during electro- Yeung, Y.B., Scott, T.B., Gopinath, S., Menon, R.M., Hsu, C.,1997. Design, fabrication and assembly of an apparatus forkinetic soil flushing of Pb-contaminated silt loam. Journal

of Environmental Engineering, ASCE 121 (11), 805–815. electrokinetic remediation studies. Geotechnical TestingJournal, GTJODJ 20 (2), 199–210.Segall, B.A., O’Bannon, C.E., Mattias, J.A., 1980. Electro-

osmosis chemistry and water quality. Journal of Geotechni- Yong, R.N., Mohamed, A.M.O., Warkentin, B.P., 1992. Prin-ciple of contaminant transport in soilsDevelopments incal Engineering, ASCE 10610, 1148–1152.

Ugaz, A., Puppala, S., Gale, R.J, Acar, Y.B., 1992. Complicat- Geotechnical Engineering 73, vol. 73. Elsevier Science,Amsterdam.ing features of electrokinetic remediation of soils and slur-

lead removal from contaminated marine clay by electrokinetic soil decontamination

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