lead (ii) removal from natural soils by enhanced electrokinetic remediation

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Science of the Total Environ

Lead (II) removal from natural soils by enhanced

electrokinetic remediation

Ahmet Altin*, Mustafa Degirmenci

Cumhuriyet University, Department of Environmental Engineering, 58140 Campus, Sivas, Turkey

Received 30 May 2003; received in revised form 10 November 2003; accepted 11 June 2004

Abstract

Electrokinetic remediation is a very effective method to remove metal from fine-grained soils having low adsorption and

buffering capacity. However, remediation of soil having high alkali and adsorption capacity via the electrokinetic method is a

very difficult process. Therefore, enhancement techniques are required for use in these soil types.

In this study, the effect of the presence of minerals having high alkali and cation exchange capacity in natural soil polluted

with lead (II) was investigated by means of the efficiency of electrokinetic remediation method. Natural soil samples containing

clinoptilolite, gypsum and calcite minerals were used in experimental studies. Moreover, a sample containing kaolinite minerals

was studied to compare with the results obtained from other samples. Best results for soils bearing alkali and high sorption

capacity minerals were obtained upon addition of 3 mol AcH and application of 20 V constant potential after a remediation

period of 220 h. In these test conditions, lead (II) removal efficiencies for these samples varied between 60% and 70% up to

0.55 normalized distance. Under the same conditions, removal efficiencies in kaolinite sample varied between 50% and 95% up

to 0.9 normalized distance.

D 2004 Elsevier B.V. All rights reserved.

Keywords: Electrokinetic remediation; Lead (II); Calcite; Gypsum; Dolomite; Clinoptilolite

1. Introduction

Heavymetals occupy an important place among soil

contaminants. Acute poisoning may occur in humans

or other living organisms due to a high intake of heavy

metals. Furthermore, the inclusion of such substances

0048-9697/$ - see front matter D 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.scitotenv.2004.06.017

* Corresponding author. Fax: +90 346 219 1177.

E-mail address: [email protected] (A. Altin).

in the ecological cycle can cause chronic illness due to

metal accumulation in the bodies of living organisms

(Sengupta, 1999). Among the heavy metal contami-

nants, lead (II) holds a distinct position due to its low

solubility and low microbial fragment ability. Today,

several methods have been developed for remediation

of contaminated soil such as soil washing/flushing,

bioventing, air sparging. Most of these methods benefit

from air or water permeability of the soil. For this

reason, these methods may be used effectively for

ment 337 (2005) 1–10

A. Altin, M. Degirmenci / Science of the Total Environment 337 (2005) 1–102

coarse-grained and highly permeable soils, whereas

applications on the fine-grained soils are fairly limited

(Ashawabkeh et al., 1999).

Methods such as solidification–stabilization and

vitrification are preferred to purify fine-grained metal

polluted soil containing high alkali and cation

exchange capacity minerals. However, stabilization

methods—due to their structure—prevent the reusage

of affected area. These negative factors mainly occur

in lengthy periods due to the excesses of the soil’s

sorption capacity or deterioration of the soil’s pH

stability. For example, nowadays, many treatment

units such as stabilization ponds and sludge drying

beds and many hazardous waste disposal areas are

changed into threading contamination source for

ground and surface water. Therefore, metal pollution

near water resources, in particular, should be

addressed regardless of the costs.

Today, one of the important methods used in fine-

grained soil treatment is electrokinetic remediation.

The efficiency of the electrokinetic remediation varies

in accordance with the mineralogical properties of the

soil. Electrokinetic remediation may be effectively

applied in the remediation of heavy metals in soils

containing clay minerals such as kaolin having a low

sorption and buffering capacity (Hamed et al., 1991).

However, studies carried out by Puppala et al. (1997)

and Reddy and Shirani (1997) pointed out that

electrokinetic treatment of soils having high alkali

and sorption capacity is very difficult; but the effect of

minerals such as clinoptilolite, gypsum, dolomite and

calcite on methods has yet to be defined.

In this study, electrokinetic treatability of soils

polluted with lead (II) and minerals cited above was

investigated, and we tried to identify optimum

operation conditions for these soil types. The obtained

results were compared with the treatment results of

other sample having high kaolinite content.

2. Background

With the application of a direct current (DC)

electrical field on contaminated soil, the charged ions

begin to migrate. This migration is such that the

negatively charged contaminants move towards the

anode while the positively charged ions move towards

the cathode (Acar and Alshawabkeh, 1993). Previous

studies regarding electrokinetic remediation have

shown that the principal mechanisms causing the

contaminant migration are electroosmosis and electro-

migration (Acar and Alshawabkeh, 1993; Puppala et

al., 1997; Chung and Kang, 1999). A brief description

of electroosmosis would be a water flow due to the

potential difference of the electrodes, and contaminants

are carried by water flow. On the other hand, in

electromigration, the application of electrical current

causes the charged ions in the pore water to move

towards the positive or negative electrodes in accord-

ance with their polarities. During electrokinetic reme-

diation, the contaminant migration in the soil and

electrodes is simultaneously achieved by such phe-

nomena as sorption/desorption, precipitation/dissolu-

tion and electrolysis. (Chung and Kang, 1999; Puppala

et al., 1997). Among these studies, some are often

useful in the removal of heavy metals through electro-

kinetic remediation, while others make the remediation

more difficult. For instance, due to electrolysis, the pH

value in the cathode area rises to 12, whereas in the

anode area it falls to 2 (Reddy and Shirani, 1997;

Probstein andHicks, 1993; Hamed et al., 1991). In such

a case, the contaminant movement in the cathode area is

hindered by precipitation reactions, whereas the con-

taminant movement in the anode area is accelerated due

to desorption and dissolution reactions (Hicks and

Tondorf, 1994). In situations such as these, to increase

the efficiency of the method, acid solutions such as

acetic acid, citric acid or complexing substance such as

ethylenediamine tetra acetic acid (EDTA) are added

(Yang and Lin, 1998).

Studies on the remediation of heavy metals from

fine-grained soils have mostly been carried out on pure

clay types such as kaolin, Na montmorillonite,

smectite, illite and their synthetically prepared mix-

tures with quartz (Darmawan and Wada, 2002).

Studies on fairly heterogeneous natural soil sam-

ples—except marsh mud, clayey sand, river mud, silt

loam, marine clay and glacial tills—are relatively

limited (Langeman, 1993; Virkutyte et al., 2002; Yang

and Lin, 1998; Chung and Kang, 1999; Reddy and

Shirani, 1997). Also, in literature, no study has been

encountered on the remediation of lead (II) from

natural soil samples containing minerals such as

calcite, dolomite, gypsum, and clinoptilolite.

The objective of this study was to examine the

efficiency and extend the applicability of electro-

Table 1

General properties of soil samples

Parameter Bestepeler

sample

Kumarli

sample

Kaolinite

sample

Method

Mineralogy (%)

Dolomite 3.3 2.4 –

Gypsum 7.4 – –

Calcite 13.33 13.0 –

A. Altin, M. Degirmenci / Science of the Total Environment 337 (2005) 1–10 3

kinetic remediation to remove lead from natural soils

containing minerals with alkali and high sorption

capacity. Furthermore, it is also aimed to determine

the electrochemical behavior of these types of soils

with the application of this method and contribute

towards the development of the theory of electro-

kinetic remediation.

Clinoptilolite 14.9 22.0 – Brindley

(1980)a

Clay 33.9 27.1 40

Quartz 3.7 7.8 60

Feldspar 23.5 27.7 –

Grain size distribution (%)

Coarse sand 8 9 ASTM

(1995a,b),

BS1370

(1995)

Medium sand 25 23 NA

Fine sand 21 26

Silt and clay 46 42

Consistency limits

Plastic limit 27.2 35.2 20.5

Liquid limit 31.5 42.5 32

Lineer crouch 3.5 5 2.3

Soil classification SM-SC SM-SC CL USBR

1974)

Pb (II) exchange

capacity

(meq/100 g)

17.4 19.3 6.56 Reddy and

Shirani

(1997)

Porosity 0.40 0.38 0.42 Calculation

Semi-quantitative percents of mineral phases of rockswere calculated

by the use of multi-componentmixtures as external standards sensu

Brindley (1980).a XRD whole-rock analyses were conducted on a Rigaku X-ray

diffractometer (type DMAX IIIC).

3. Materials and methods

3.1. Soil properties

In this study, three different soil samples were used.

The first two samples were taken from near the Kumarli

and Bestepeler landfill areas in Kayseri City (Turkey).

Other sample is powder kaolinite produced by a deposit

near the city of Canakkale. The properties of these

samples and used experimental methods are summar-

ized in Table 1. It can be seen in Table 1 that soil

samples from Kumarli and Bestepeler contain signifi-

cant amounts of calcite, gypsum, dolomite, clinoptilo-

lite and clay minerals. In particular, components such

as dolomite, calcite and gypsum, due to increasing the

buffering effect on soil, cause precipitation reactions

during electrokinetic remediation (Puppala et al.,

1997). Clinoptilolite, being a volcanic material,

adsorbs the metallic contaminants (Beyazit et al.,

2002) and extends in the electrokinetic remediation

period. Peaks of clay minerals in the graphs of XRD

analysis of all rocks are seen in the area of 5–7 and 19–

208 of 2h angles. Peaks in these areas generally defined

as smectite and illite type clays. These type of clays

form the other effect causing an increase in the sorption

capacity of the samples.

3.2. Test apparatus

The electrokinetic remediation apparatus adapted

from Hsu (1997) primarily consisted of an electro-

kinetic extraction cell, fluid volume and gas volume

measurement devices, a DC electrokinetic power

supply and a multimeter (Fig. 1). Electrokinetic

extraction cell includes a specimen cylinder (7.5�15

mm, D�L) made of PVC, two end flanges that house

a purging solution reservoir and graphite electrodes/

7.5�3 mm, D�W) and voltage measurement probes

made of steel. The flow volume and gas volume

measurement devices consist of four 350-mm-long

glass cylinders. Internal diameter of cylinders used in

gas measurement and fluid measurement are 12 and

35 mm, respectively.

3.3. Sample preparation

The amount of soil used in experimental studies is

1.5 kg. Pb(NO3) solutions were added to soil in order to

produce lead (II) contaminants of about 1000 and 4000

mg/kg. The soil–contaminant mixture was manually

mixed. To achieve a homogeneous contaminant con-

centration and moisture content, the mixture was put

aside for 48 h. Prepared slurry was transferred into

specimen cylinder and compacted by the consolidation

method described in Reddy et al. (1997). Finally,

Fig. 1. Electrokinetic remediation apparatus (adapted from Hsu, 1997).


excess portions found at the edges of the cell were

shaved away and the specimen cylinder was assembled

in the electrokinetic extraction cell.

3.4. Electrokinetic remediation tests

After placing 1000 and 4000 ppm lead (II)

contaminated soils in the test apparatus, under 10

and 20 V constant potential, the sample was

subjected to electrokinetic remediation for different

remediation periods and different conditions.

Throughout the test process, the current through

the soil sample and changes in the fluid level in the

fluid–gas measurement cylinders were continuously

monitored. At the end of electrokinetic remediation

tests, soil samples were disassembled from the

apparatus and sliced into six sections. The values

of pH and lead (II) concentration were measured in

each slice. In the measurement of lead (II) and pH,

methods suggested by Hamed et al. (1991) and

McLean (1982) were used, respectively. The testing

program is summarized in Table 2.

4. Results and discussion

4.1. Electroosmotic flow

The contaminant flow during the electrokinetic

remediation is mostly governed through electromigra-

Table 2

Summary of testing program

Sample Test no. Pb (II) (ppm) Voltage (v) Duration time (hour) PH Purging solution

Bestepeler Sample

Test-1 4000 20 233 7.79 H2O

Test-2 4000 10 137 7.91 3 M AcH

Test-3 4000 10 473 7.40 0.5 M AcH

Test-4 1000 20 220 8.06 3 M AcH

Test-5 1000 10 240 7.95 3 M AcH

Kumarli Sample

Test-6 4000 20 233 7.92 H2O

Test-7 4000 10 137 7.98 3 M AcH

Test-8 4000 10 473 7.41 0.5 M AcH

Test-9 1000 20 220 8.06 3 M AcH

Test-10 1000 10 240 7.91 3 M AcH

Kaolinite Sample

Test-11 4000 20 233 4.92 H2O

Test-12 4000 10 137 4.95 3 M AcH

Test-13 4000 10 473 5.18 0.5 M AcH

Test-14 1000 20 220 4.51 3 M AcH

Test-15 1000 10 240 4.62 3 M AcH


tion, electroosmosis and diffusion (Acar and Alsha-

wabkeh, 1993; Ashawabkeh et al., 1999). For this

reason, electroosmosis flows occurring under different

experimental conditions were measured and results

are presented in Fig. 2.

Electroosmotic flow is directly related to soil zeta

potential, which is a complex function of soil properties

and chemical composition of pore water (Reddy et al.,

2001). As the negativity of soil zeta potential increases,

electroosmotic flow also increases. As can be seen in

Fig. 2, negative electroosmosis flows (excluding Test-

1) were observed in the Bestepeler and Kaolinite

samples during the initial 0–50 h interval. A similar

situation was observed in the Kumarli sample for Test-

7 and Test-8 only (Fig. 3). Based on this observation, it

may be said that the zeta potential of the Kumarli

sample has a more negative value than that of the

Bestepeler and Kaolinite sample. Furthermore, a high

metal concentration causes a decrease in soil’s zeta

potential. This situation is clearly seen in the results

obtained from Test-2, Test-5, Test-7, Test-10, Test-12

and Test-15 (given in Fig. 2). Another result shown in

Fig. 2 is that electroosmotic flow increases by applying

high voltage to system. Test-4, Test-5, Test-9, Test-10,

Test-14 and Test-15 clearly show this situation. Similar

results were also reported by Shapiro and Probstein

(1993).

It is known that hydroxyl ions in the cathode area

increases the medium pH and yields to sedimentation

reaction in the electrokinetic treatment method.

Therefore, electroosmotic flow in the sample of

Bestepeler and Kumarli decreases or completely stops

during the later hour of electrokinetic treatment.

However, it is observed that AcH used as purging

solution in tests reduces the sedimentation reaction in

the cathode area and causes electroosmotic flow. This

effect is much clearer in the Kumarli sample as given

in Fig. 2. The alkali mineral content of Kumarli

sample is less than in Bestepeler sample (see Table 1).

Therefore, the Kumarli sample is better tamponed by

AcH and results in better electroosmotic flow. It is

thought that the reason for low electroosmotic flow of

kaolonite is the low zeta potential.

4.2. Variations in soil pH

When an electrical charge is applied to the saturated

soils, an electrolysis reaction of water takes places at

the electrodes. Oxygen and hydrogen ions are pro-

duced at the anode, and hydrogen and hydroxide ions

are produced at the cathode. These ions migrate toward

cathode or anode, depending on their polarities, via

electroosmosis, electromigration and diffusion (Acar

et al., 1994). Thus, changes in soil pH profiles between

anode and cathode hinders contaminant migration. In

order to determine these phenomena, pH variations of

soil sample were measured and the results obtained are

shown in Fig. 3.

Puppala et al. (1997) determined that pH value

below 6 would be sufficient to dissolve and remove the

lead (II) from the soil. Virkutyte et al. (2002) also

reported that precipitation reactions are at a minimum

Fig. 3. The pH profile in electrokinetic remediation under differen

test conditions.

Fig. 2. Variation of the electroosmotic flow with time under

different test conditions.


level if the pH value is below 4.5. As seen in Fig. 3, pH

values at the regions near the cathode increased up to 11

in the unenhanced electrokinetic remediation tests

(Test-1, Test-6 and Test-11). Based on this, it may be

said that during Test-1, Test-6 and Test-11 precipitation

reactions occurred in the area near the cathode, whereas

dissolution reactions occurred in the area near the

anode.

In the electrokinetic remediation of soils having

minerals of high alkali and high sorption capacity,

the metal movement is dependent on the speed of

the H+ cloud at the anode moving towards the

cathode. However, the speed of the H+ cloud is

limited by calcite, dolomite and gypsum minerals.

When the data obtained from unenhanced tests are

taken into consideration, this phenomenon is seen to

be more prominent in the Kumarli and Bestepeler

samples.

According to Fig. 3, the addition of AcH into the

cathode reservoir caused a buffering effect of the

high pH values observed in the unenhanced tests, and

reduced the pH values to between 4 and 6. On the

other hand, it may also be said that the application of

3 mol AcH in Test-2 and Test-7 caused buffering in a

shorter time as compared to Test-3 and Test-8 where

0.5 mol AcH was applied. For the kaolinite sample,

high pH values in the cathode area were completely

neutralized and fell to 5 after 473 h when 0.5 M AcH

was used (Test-13). This pH value in Test-15 was

t

Fig. 4. The lead profiles in eletrokinetic remediation under differen

test conditions.


decreased to about 4 at the end of 220 h when 3 M

AcH was used.

4.3. Lead (II) removal efficiencies

In heterogeneous soils, the presence of the calcite,

gypsum, dolomite, clinoptilolite, smectite, etc.,

increases the soil’s pH and sorption capacity and

sometimes hinders the metal movement by precip-

itation and sorption reactions. For this reason, it is

quite difficult to perform electrokinetic remediation

on soil containing such minerals. In this study, two

lead (II)-contaminated soil samples containing the

aforementioned minerals and one kaolinite sample

were subjected to electrokinetic remediation under

different potential energy and contaminant concen-

trations, and the results are presented in Fig. 4.

As seen in Fig. 4, lead (II) accumulations occurred

near the cathode, while lead (II) concentrations

decreased in areas close to the anode in all of the

unenhanced remediation tests (Test-1, Test-6 and Test-

11). In these tests, lead (II) removal efficiency of

kaolinite sample is better than the other samples. This

phenomenon directly relates to the mineralogical

structure of the soil samples. For example, due to the

low sorption and buffering capacity of kaolinite

sample, H+ clouds at the anode area were transported

by electromigration, and lead (II) transport in the

kaolinite sample became easier. However, Kumarli and

Bestepeler samples have a more heterogeneous com-

position than the kaolinite sample. Therefore, gypsum,

dolomite and calcite minerals in these samples

decreased the transportation of H+ clouds towards the

cathode. Furthermore, lead (II) transport was hindered

by minerals having high sorption capacity such as

clinoptilolite in these samples. These phenomena are

clearly observed in Test-1 and Test-6. When the

removal efficiencies obtained from Test-2 and Test-7

(which used 3 M AcH) are taken into consideration, it

can be said that results in Test-2 and Test-7 are similar

to Test-1 and Test-6. However, as seen in Table 1,

remediation times and voltage usage in Test-2 and Test-

7 are less than those used in Test-1 and Test-6 by about

40% and 50%, respectively. It means that energy costs

are reduced by using AcH as the purging solution.

According to Chung and Kang (1999), the transport

of lead (II) at low levels of concentration is slower

because almost all of the lead is adsorbed to the soil

t

particle. Alternatively, at high levels of concentration,

the transport of lead (II) becomes faster becausemost of

the lead (II) is free in the pore and is not adsorbed to the

soil particle. This phenomenon is confirmed by the

results obtained from Test-12 and Test 15. However,

low removal efficiencies were seen at high levels of

metal concentrations when Test-2 and Test-7 are

compared with Test-5 and Test-10. These disparities

relate to the high sorption capacities of the Bestepeler

and Kumarli samples. When the clay and clinoptilolite

quantities of these samples are investigated, it is seen

that the clay minerals in the Kumarli sample are lower

and clinoptilolite minerals are higher than Bestepeler

sample (Table 1). Beyazit et al. (2002) determined that

Fig. 5. Cumulative gas production in the test system in 10-vol

constant potential.


the cation exchange capacity (CEC) of clinoptilolite

varied between 200 and 400 meq/100 g, and it is 2–3

times higher than clay minerals having high CEC.

In contaminated soils with lead (II), many precip-

itation reactions take place on the basis of pH and

mineralogy of soils, and compounds of low solubility

such as lead (II) sulphate and lead (II) carbonate occur

in soil. According to Puppala et al. (1997), soil pH

should be kept below 6 to hinder these precipitation

reactions. Virkutyte et al. (2002) report that these

reactions occur at their lowest level when pH is

between 4 and 4.5. Within the scope of the study,

Kumarli and Bestepeler samples generally have a

similar mineralogical composition. However, the Bes-

tepeler sample contains a significant proportion of

gypsum and dolomite. Disparities between these

samples affect the efficiencies of enhanced electro-

kinetic remediation. In particular, when Test-2 is

compared to Test-9, it may said that alkali minerals in

the Bestepeler sample increase the precipitation of lead

(II) and neutralization of high pH at cathode area by

using AcH.

As seen in Fig. 4, best results for Kumarli and

Bestepeler samples were obtained by adding 3 mol

AcH and applying 20 V constant potential (Test-4,

Test-9 and Test 14) after a remediation period of 220

h. In these test conditions, lead (II) removal efficien-

cies for Kumarli and Bestepeler samples varied

between 60% and 70% up to 0.55 normalized

distance. Under the same conditions, removal effi-

ciencies in kaolinite sample varied between 50% and

95% up to 0.9 normalized distance.

4.4. Gas production during electrokinetic remediation

The production of gases at the anode and cathode

reservoirs is the phenomenon observed during

electrokinetic remediation. Due to electrolysis, O2

and H2 gases are released at the anode and cathode

reservoirs. According to Faraday’s law, assuming that

the efficiency of water electrolysis is 100%, the

passage of 1 mol of electrical charge through the

system causes the formation of 0.5 mol H2 and 0.25

mol O2 (Hsu, 1997). However, during electrokinetic

remediation, the heterogeneous composition of the

pore water and the fluids in the electrode reservoirs,

and electromigration and electroosmosis and move-

ment of the H+ and OH� ions, the gas produced is

t

actually much lower. To determine the change in the

amount of H2 gas produced in the system over time,

gas measurements under the 10 V of constant

potential were carried out and the results are

presented in Fig. 5.

As seen in Fig. 5, for all soils, the gas

produced over time changes logarithmically. Within

the first 24 h the gas production rate is high, and

slows down after 35–40 h. According to Shariatma-

dari (1997), this reduction is dependent on the

decrease in the amount of current passing through

the system and the migration of the H+/OH� ions

due to electromigration.

Another result that may be extracted from Fig. 5 is

that gas production in the Kumarli sample was

proportionally higher than the Bestepeler sample. It

is thought that the source of this augmentation may

well be the high content of alkali minerals in the

Kumarli sample.

4.5. Energy expenditures

One of the cost items involved in the electrokinetic

remediation is energy expenditure. Virkutyte et al.

(2002) expressed that in site applications, the cost of

energy expenditures constitutes 10–15% of the total

costs. For this reason, the energy consumed over time

during experimental studies was continually meas-

ured, and the average energy expenditure for each test

was recorded and is presented in Table 3.

As seen in Table 3, the energy expenditures of the

Bestepeler andKaolinite sampleswere lower than in the

Kumarli sample. Puppala et al. (1997) determined that

in electrokinetic remediation, energy expenditures

Table 3

Energy expenditures in electrokinetic remediation tests

Bestepeler sample Kumarli sample Kaolinite sample

Test

no.

Energy

expenditure

(kW h/m3

soil)

Test

no.

Energy

expenditure

(kW h/m3

soil)

Test

no.

Energy

expenditure

(kW h/m3

soil)

Test-1 45 Test-6 70 Test-11 20

Test-4 85 Test-9 160 Test-14 45

Test-5 75 Test-10 95 Test-15 40


increase with the increase in the soil sorption capacity.

The results given in Table 3 for the Kumarli sample

support this observation. Also, Puppala et al. (1997)

state that energy expenditures are reduced by using

acetic acid in enhanced electrokinetic remediation.

However, at first sight, the data presented in Table 3

seem tobe contrary to this attribute. Furthermore, taking

into consideration that AcH increased the efficiency of

the remediation and that the output obtained fromTest-1

and Test-6 were obtained in a shorter period, it may be

concluded that remediation completed with AcH

required less total remediation costs.

5. Conclusions

In this study, the applicability of electrokinetic

remediation in the removal of lead (II) from two

different natural soils having a high sorption and

buffering capacity was examined. Conclusions

derived from the experimental studies have been

summarized as follows:

! Direction and quantity of electroosmotic flow is

generally related to the zeta potential of the soil.

When the negativity of the zeta potential

increases and the velocity of the electroosmotic

flow also increases, the direction of the electro-

osmotic flow generally leads towards the cathode

and the velocity of the electroosmotic flow also

increases. High levels of metals in soil reduce the

negativity of the zeta potential and cause negative

electroosmotic flow in the initial hours (generally

the first 50 h) of electrokinetic remediation. In

addition, hydroxyl ions generated from the

cathode due to electrolysis cause precipitation

reactions to slow down or to stop completely.

However, these negative factors may be hindered

by using AcH as purging solution.

! High pH levels at the cathode area in the

unenhanced electrokinetic remediation may be

decreased to the range of 4 and 6 by adding 3 M

AcH into cathode reservoir for soils containing

alkali and high sorption capacity minerals. How-

ever, similar pH values may be reached at longer

remediation times by using 0.5 M AcH.

! Minerals in soils such as gypsum, dolomite calcite

and clinoptilolite decrease the efficiency of elec-

trokinetic remediation due to the hindrance in the

transportation of H+ clouds towards the cathode as

well the desorption of metals. However, electro-

kinetic remediation time may be decreased by 40%

and energy costs may also be reduced by 50% by

using 3 M AcH as purging solution.

! The effect on electrokinetic remediation of cli-

noptilolite minerals is higher than other clay

minerals. It is estimated that this phenomenon is

generated from the sorption capacity of clinopti-

lolite minerals which is 2–3 times higher than the

sorption capacity of clay minerals.

! In contaminated soils with lead (II), many of

the precipitation reactions that took place

depend on the pH of the soil, and compounds

of low solubility such as lead (II) sulphate and

lead (II) carbonates occurred in the soil. More-

over, these minerals also reduced the desorption

of contaminants.

! Gas production during electrokinetic remediation

decreases logarithmically. Furthermore, the quan-

tity of alkali minerals in the soil also increased the

speed of gas production in the electrodes.

! Soil mineralogy has a substantial impact on

energy expenditures and removal efficiencies. In

particular, energy expenditures rather increase in

the case of soils containing clinoptilolite. How-

ever, using AcH as the purging solution signifi-

cantly decreases the remediation time and

remediation costs.

Acknowledgements

This study was financially supported by the

Cumhuriyet University Scientific Research Fund as

a PhD thesis (Project Code No, M-169).


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