Chemosphere 90 (2013) 2326–2331

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Chemosphere

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Technical Note

Enhanced-electrokinetic remediation of copper–pyrene co-contaminated soilwith different oxidants and pH control

Long Cang, Guang-Ping Fan, Dong-Mei Zhou ⇑, Quan-Ying WangKey Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China

h i g h l i g h t s

" A new technology was developed to decontaminate a compound contaminated soil." The highest removal percent of soil pyrene and Cu was 52% and 94%, respectively." Acid catholyte (pH = 3.5) and application of Na2S2O8 was the best operation condition." The reduction product of KMnO4 prevented the migration of Cu.

a r t i c l e i n f o

Article history:Received 29 May 2012Received in revised form 8 October 2012Accepted 10 October 2012Available online 22 November 2012

Keywords:ElectrokineticPyreneCopperOxidantSoilRemediation

0045-6535/$ - see front matter � 2012 Elsevier Ltd. Ahttp://dx.doi.org/10.1016/j.chemosphere.2012.10.062

⇑ Corresponding author. Tel.: +86 25 86881180; faxE-mail address: dmzhou@issas.ac.cn (D.-M. Zhou).

a b s t r a c t

Electrokinetic (EK) remediation has potential to simultaneously remove heavy metals and organic com-pounds from soil, but the removal percent of these pollutants is very low in general if no enhancing treat-ment is applied. This study developed a new enhanced-EK remediation technology to decontaminate aheavy metal–organic compound co-contaminated soil by applying different oxidants and pH control. Ared soil was used as a model clayed soil, and was spiked with pyrene and Cu at about 500 mg kg�1 forboth to simulate real situation. Bench-scale EK experiments were performed using four oxidants(H2O2, NaClO, KMnO4, and Na2S2O8) and controlling electrolyte pH at 3.5 or 10. After the treatments with1.0 V cm�1 of voltage gradient for 335 h, soil pH, electrical conductivity, and the concentrations andchemical fractionations of soil pyrene and Cu were analyzed. The results showed that there was signifi-cant migration of pyrene and Cu from the soil, and the removal percent of soil pyrene and Cu varied in therange of 30–52% and 8–94%, respectively. Low pH favoured the migration of soil Cu, while KMnO4 was thebest one for the degradation of pyrene among the tested oxidants, although it unfortunatelyprevented the migration of soil Cu by forming Cu oxide. Application of Na2S2O8 and to control thecatholyte pH at 3.5 were found to be the best operation conditions for decontaminating the Cu-pyreneco-contaminated soil.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

Thousands of sites are contaminated with both heavy metalsand organic compounds, which brought the difficulties and chal-lenges for soil remediation. According to the reports of USEPA,more than 67% of contaminated sites are found to contain heavymetals and organic pollutants simultaneously (USEPA, 2004). Forsuch heavy metal–organic compound polluted soils, there has noappropriate technology to decontaminate them because of theirenormous property difference. Heavy metals are usually water/acid-soluble, easily migrated and integrated with soil Fe–Mn oxi-des and organic matter. In contrast, most of organic pollutantsare hydrophobic, easily integrated with soil organic matter and dif-

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ficult to be removed. Therefore, the remediation of heavymetal–organic compound co-contaminated soil is difficult andchallenging.

Electrokinetic (EK) remediation is a technology that was intro-duced for soil and groundwater remediation around 1980s. Thetechnology applies DC electric field in soil to generate a voltagegradient driving soluble pollutants out of soil by electromigration,electroosmosis and/or electrophoresis (Acar and Alshawabkeh,1993; Probstein and Hicks, 1993). Electromigration is the mainmigration mode for heavy metals, and electroosmosis is the mainmigration mode for organic pollutants.

Some previous studies showed that EK technology had potentialto remove heavy metals and organic compounds from soil simulta-neously (Maini et al., 2000). However, EK remediation itself cannotremove heavy metals and organic pollutants at the same time be-cause of the accumulation of heavy metals near cathode for high

L. Cang et al. / Chemosphere 90 (2013) 2326–2331 2327

soil pH over there and the weakly migration of organic pollutantsfor their hydrophobicity. Recently, some enhanced-EK remediationtechnologies are used to decontaminate the compound soil. The re-search group of Reddy at University of Illinois at Chicago had car-ried out lot of works about cosolvent-enhanced EK remediation(Maturi and Reddy, 2006, 2008; Reddy and Ala, 2006; Reddyet al., 2006; Maturi et al., 2009). In their studies, some cosolvents(Igepal CA-720, Tween 80, HP-b-CD, n-butylamine and so on) areused. However, a large amount of heavy metals were still accumu-lated in the soil near the cathode. The organic pollutants moved tothe anolyte or catholyte according to the direction of electroosmo-sis, and the electrolyte containing organic pollutants needs to befurther treated. The removal percent of pollutants was low, espe-cially for heavy metals. Oxidant-enhanced EK remediation technol-ogy can oxidize the organic pollutants during the migration oforganic pollutes. Reddy and Karri (2008) studied the oxidant-enhanced EK remediation technology to decontaminate the nickeland phenanthrene compound soil by adding H2O2 solution in elec-trolyte. About 28–57% phenanthrene were removed from soil. Inthe case of no pH control, few amount of nickel was removed forthe high soil pH.

In this study, the main objective was to achieve the simulta-neous removal of Cu and pyrene from soil. By applying differentoxidants in electrolyte and controlling soil pH, we want to driveCu to electrolyte and degrade pyrene during their migration pro-cess. Through this study, a new technology to decontaminate theco-contaminated soil was developed, and the remediation mecha-nism was disclosed. It will help us to develop the remediation tech-nology for heavy metals–organic co-contaminated soil.

2. Materials and methods

2.1. Soil

A red soil (Udic Ferrosols) was sampled from barren surface soil(0–20 cm depth) in Yingtan County, Jiangxi Province, China. Soilsamples were air-dried and sieved through a nylon sieve(0.84 mm). Its cation exchange capacity (CEC) was 24.8 cmol (+)kg�1. The soil pH, electrical conductivity (EC, 1:2.5 soil to water),and organic carbon (SOC) were 4.80, 28 lS cm�1, and 3.75 g kg�1,respectively. The background values of soil Cu, Zn, Pb and Cd were27, 25, 60, and 0.04 mg kg�1, respectively. No PAHs were detectedin the soil.

The pyrene-Cu co-contaminated soil represents typical contam-inates found at some contaminated sites. It was prepared by spik-ing CuCl2 and pyrene (each at about 500 mg kg�1 as Cu and pyrene)according to the following method. First, the red soil (300 g, 10%total quantity of soil to be spiked) was spiked with a highly purepyrene (1.500 g, Sigma 98%) in acetone. The spiked soil was trans-ferred in a wide rectangular pan and then left under the fume hoodfor 1 d to evaporate any traces of acetone. Second, the spiked soilwith pyrene were further spiked with 30 mL CuCl2 solution (con-taining 4.027 g CuCl2�2H2O) and put in the fume hood for 1 d.Third, the spiked soil (300 g) was thoroughly mixed with uncon-taminated soil (2700 g), and then the total contaminated soil waspassed through a 0.84 mm nylon sieve again to ensure homogene-ity of treatment. The final concentrations for pyrene and Cu in thetreated soil were analysed, and their values were 486 and524 mg kg�1, respectively.

2.2. Experimental design

The set-up used for EK experiments and pH control system issimilar with that in our previous studies (Zhou et al., 2004; Canget al., 2007). As shown in Table 1, there were five treatments in this

trial. Different oxidants (6% H2O2, 0.1% NaClO, 9 g L�1 KMnO4 and0.5 M Na2S2O8) and pH control were used. The concentrations ofdifferent oxidants were confirmed according to some references(Thepsithar and Roberts, 2006; Cang et al., 2007; Reddy and Karri,2008). 1.0 M NaOH and 1.0 M HCl were applied to control the pH inthe anolyte and catholyte, respectively. The applied voltage gradi-ent was 1.0 V cm�1. During the experiments, electric currents, elec-troosmotic flow (EOF), electrolyte pH, and EC were monitored.After the treatments, each soil column was divided into five equalsections, labelled as S1–S5 from the anode to the cathode. The soilpH, EC, and the contents and chemical fractionations of pyrene andCu in soil subsamples were determined. According to the soilweight and the contents of pyrene and Cu in S1–S5, the total re-moval percents of pyrene and Cu were calculated.

2.3. Chemical analysis

All chemicals used in the experiments were of analytical grade,and deionized water was used to prepare all solutions. Soil pH, EC,CEC, and SOC were analyzed using conventional analytical meth-ods (Lu, 2000). The soil pH and EC were determined by a pH meter(Shanghai REX Instrument, model pHS-3B, China) and an EC meter(Shanghai REX Instrument, model DDS-11A, China), respectively,with a ratio of 1:2.5 soil to water. SOC and CEC were analyzed bydichromate oxidation method and ammonium acetate extractionmethod, respectively.

Soil samples were air-dried, and part of the samples wereground to pass through a 100-mesh nylon sieve (0.149 mm), andthen digested with HF–HNO3–HClO4 for determination of total soilCu concentration by a Hitachi Z-2000 Atomic Absorbance Spec-trometer. Two Chinese national standard soil samples(GBW07406 and GBW07407) were used for checking. The chemicalfractionations of Cu in soil subsamples were performed accordingto BCR (European Community Bureau of Reference) method (Ureet al., 1993) with four fractions: F1 acid soluble form; F2 Fe–Mnoxide bound form; F3 organically bound form; F4 residual form.

The procedure utilized to extract soil total pyrene was modifiedfrom USEPA 3550B (Sun et al., 2010). The soils were air-dried,homogenized, and passed through a 20 mesh stainless steel sieve(0.84 mm). The soil extracts were analyzed using a HPLC (Agilent1100, USA) fitted with a reverse phase C18 column (LC-PAH250 mm � 4.6 mm, 5 lm, Supelo, USA). Acetonitrile (Sigma, USA)was used as the mobile phase at a flow rate of 1.5 mL min�1. Chro-matography was performed at 30 �C and pyrene was detected at254 nm with ultraviolet detection, and their detection limitationwas 0.36 ng L�1. The average recovery efficiency was 112% (n = 4,relative standard deviation less than 1.3%) for pyrene. The bioavail-able pyrene content in soil was performed as described by Patonet al. (2009). 2 g of soil sample was shaken in 20 mL of 10% HPCD(hydroxypropyl-beta-cyclodextrin) solution for 24 h at 25 �C fol-lowed by 4000 rpm centrifugation. Then, 10 mL of the solvent frac-tions were mixed with 10 mL n-hexane by vortex for 1 minfollowed by 4000 rpm centrifugation. 5 mL of organic phase fromthe solvent fractions was evaporated by nitrogen gas and ex-changed by acetonitrile with a final volume of 2.0 mL. After filtra-tion through 0.22 lm filter, the treated soil extracts were analyzedusing a HPLC according to the similar method as for the total soilpyrene.

3. Results and discussion

3.1. Change of electric current and EOF

Fig. 1 shows the change of electric current and EOF across thesoil column with time for different treatments. From Fig. 1a, the

Table 1Experimental design of electrokinetic treatments.

Treatments Anolyte (10% HPCD + 0.01 M NaNO3) Catholyte (0.01 M NaNO3) pH control Soil weight (g)

Exp-01 Without control 535Exp-02 6% H2O2 Catholyte pH = 3.5 535Exp-03 0.1% NaClO Anolyte pH = 10 535Exp-04 9 g L�1 KMnO4 Catholyte pH = 3.5 520Exp-05 0.5 M Na2S2O8 Catholyte pH = 3.5 530

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tric

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nt (m

A)

Exp-01Exp-02Exp-03Exp-04Exp-05

(a)

Fig. 1. Change of electric current (a) and electroosmotic flow (b) with time duringelectrokinetic treatments. Positive and negative values in (b) represent theelectroosmotic flow towards the cathode and the anode, respectively.

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S1 S2 S3 S4 S5

Soil section (from anode to cathode)

(b)

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EC (m

S cm

-1)

Fig. 2. Change of soil pH (a) and EC (b) in different soil sections after treatments.

2328 L. Cang et al. / Chemosphere 90 (2013) 2326–2331

current in the first 4 h reached the maximum 10.4 mA, and thengradually reduced to about 1 mA in Exp-01. In Exp-02, -03, and-04, the electric currents were low and varied from 5 to 25 mA.The electric current in Exp-05 was the highest among all the treat-ments and the peak value of electric current was 242 mA at 199 h.The Na2S2O8 solution has the highest EC (202 mS cm�1) and strongacidity to acidize soil, which leads to the highest electric currentamong all the treatments. After 199 h treatment, the electric cur-rent decreased along with the decomposition of Na2S2O8.

From Fig. 1b, the direction and volume of EOF were differentamong the five treatments. In Exp-01, the EOF moved to the cath-ode because of the negative charge in red soil surface, and the EOFvolume was 84 mL. The EOF also moved to cathode during theexperiment due to the control of anolyte pH at 10 in Exp-03, andits volume was higher than that in Exp-01. In Exp-02 and -04,the EOF moved to cathode at first and then reversed toward the an-

ode after 264 and 120 h, respectively, which were attributed to thechange of soil net surface charges as pH control at 3.5 in the cath-olyte (Yang and Lin, 1998; Zhou et al., 2004). In Exp-05, the EOFmoved to the anode at first and then turned to the cathode after120 h. This result was not according with the general rule andmight be attributed to the damage of soil particle structures forthe high electric current and strong acidity of Na2S2O8 in Exp-05.

3.2. Change of soil pH and EC

Fig. 2a shows the change of soil pH in different soil sectionsafter the treatments. In Exp-02 and -04, the soil pH values variedfrom 1.9 to 3.5 because of pH control at 3.5 in the catholyte. How-ever, the soil pH values ranged from 2.8 to 5.9 without pH controlin Exp-01 and from 5.1 to 10.8 with pH control of anolyte at 10.0 inExp-03. The soil pH values in Exp-05 ranged from 1.9 to 2.2 andwere the lowest among the five treatments, which might be dueto the high electric current and the catholyte pH control at 3.5. SoilEC values increased compared to the initial condition after thetreatments (Fig. 2b). It is ascribed to the transport of ions from

Table 2Total pyrene and Cu contents in soil sections after 335 h treatments (mg kg�1).

Pollutants Treatments Initial Soil section (from anode to cathode) Removal percent (%)

S1 S2 S3 S4 S5

Pyrene Exp-01 486 318 362 324 351 362 30Exp-02 486 239 271 298 276 312 43Exp-03 486 259 356 427 308 284 33Exp-04 486 335 380 372 64 25 52Exp-05 486 192 259 267 257 255 50

Cu Exp-01 524 53.9 113 181 624 1494 8Exp-02 524 66 100 120 169 364 69Exp-03 524 130 250 321 340 989 23Exp-04 524 40 62 89 152 2057 8Exp-05 524 27 28 31 33 40 94

L. Cang et al. / Chemosphere 90 (2013) 2326–2331 2329

electrolytes into the soil as a consequence of pH control of the elec-trolytes (Zhou et al., 2004; Cang et al., 2007). The soil EC values inExp-02, -04, and -05 were higher than those in Exp-01 and -03.This tendency was opposite to the change of soil pH, as describedabove. The lower the soil pH, the higher the soil EC.

3.3. Removal of pyrene and Cu from the soil

The total pyrene and Cu concentrations in the soil sections aftertreatments are shown in Table 2. After enhanced treatments, thetotal pyrene concentrations were lower than the initial pyrene con-centration (486 mg kg�1). The removal percent of pyrene in Exp-01was lower than those in other treatments, which indicated thatoxidants were favourable to the removal of pyrene. In Exp-02,the removal percent of pyrene was 43% and the pyrene concentra-tions in soil sections increased from the anode to the cathode byadding H2O2 in the anolyte, which was attributed to the Fenton-like oxidation by H2O2 added in the anolyte and the acid conditionsproduced by EK (Reddy and Chandhuri, 2009). In all the experi-ments, the highest removal percent of soil pyrene was 52% inExp-04, especially reached 87% and 95% in S4 and S5 respectively,and was higher than those in other soil sections. When KMnO4

with weak mobility was applied in the catholyte, the soil pyrenenear the cathode was easily oxidized, which was similar with theresults of Thepsithar and Roberts (2006). In Exp-05, the removalpercent of pyrene was 50%, and the pyrene concentrations in dif-ferent soil sections were similar, which was attributed to the stron-ger oxidability (S2O2�

8 ! 2SO��4 ) and mobility of Na2S2O8.For the removal of soil Cu, there were different removal efficien-

cies among the different treatments. From Table 2, the total soil Cuconcentrations decreased, and the Cu concentrations in the soilsections increased from the anode to cathode, which indicated thatCu moved from anode to cathode and migrated out of the soil col-umn. In Exp-01, the removal percent of Cu was only 8% and a lot ofCu was precipitated and accumulated in S4 (624 mg kg�1) and S5(1494 mg kg�1) due to high soil pH (6.0) near the cathode. Theseresults were similar with the results in Exp-04. By controlling thecatholyte pH at 3.5, Cu was dissolved from soil S1–S4 and migratedto the cathode. However, a substantial amount of Cu was accumu-lated in S5 and could not move to the catholyte, and the removalpercent of Cu was only 8%. This may be attributed to the fact thatthe decomposition products of KMnO4 and Cu ions formed newsubstances, which were adsorbed on the soil minerals (Roachand Reddy, 2006). In Exp-03, NaClO and alkaline condition (anolytepH control at 10) were disadvantageous for the migration of Cu,and the removal percent of soil Cu was 23%. The removal percentsof soil Cu in Exp-02 and -05 were 69% and 94%, respectively, andwere higher than those in other treatments, which was attributedto the lower soil pH by controlling the catholyte pH at 3.5 (Fig. 2a).The higher electric current and lower pH lead to the higher

removal percent of soil Cu in Exp-05. Meanwhile, the strong oxida-bility of Na2S2O8 destroyed the soil structures and promoted thedissolution and migration of soil Cu. According to the above results,the control of catholyte pH and addition of Na2S2O8 solution arethe best treatment for the simultaneous removal of pyrene and Cu.

3.4. Change of different fractionations of soil pyrene and Cu

Fig. 3 shows the HPCD-extracted pyrene concentration in differ-ent soil sections. After all the treatments, the HPCD-extracted pyr-ene concentrations in soil decreased. About 50% HPCD-extractedpyrene were removed, and the HPCD-extracted pyrene concentra-tions were similar between Exp-01 and -03. The HPCD-extractedpyrene concentrations in Exp-02 were higher than those in Exp-01 and -03, which might be attributed to that the addition ofH2O2 transformed the pyrene into the bioavailable pyrene(HPCD-extracted pyrene). The HPCD-extracted pyrene concentra-tions in Exp-04 and -05 were lower than those in other treatments,which was similar with the distribution of total pyrene and attrib-uted to the strong oxidability of KMnO4 and Na2S2O8 to pyrene.

Fig. 4 shows the percent of different Cu fractionations in soilafter the treatments. The percents of initial acid soluble (F1), Fe–Mn oxide bound (F2), organically bound (F3), and residual fractio-nations (F4) of Cu were 65%, 11%, 10% and 14%, respectively. Afterthe EK process, the soil Cu moved to the cathode and its concentra-tion increased from anode to cathode. Soil Cu in Exp-01 and -03moved to the cathode and was accumulated in S5 because thehigher soil pH in S5 hindered the Cu migration to the catholyte.The percents of different Cu fractionations in S5 were all higherthan those in initial soil and S1–S3. In Exp-04, the Cu accumulatedin S5 and the percents of Fe–Mn oxide bound fractionation andresidual fractionation increased to 171 and 25% of total Cu concen-tration. These results may be attributed to the reductive product ofKMnO4 (Siegrist et al., 2002). The soil pH values in different soilsections were lower in Exp-02 and -05, so the percent of differentCu fractionations decreased significantly, especially in Exp-05.

3.5. The removal mechanism of Cu and pyrene during EK remediation

To our knowledge, this is the first study in discussing the effectof different oxidants and pH control on the removal percent of hea-vy metals and organic pollutants. By adding appropriate oxidantsand controlling electrolyte pH together, the heavy metal–organiccompound contaminated soil was successfully decontaminated,and the highest removal percent of soil Cu and pyrene was 94%and 50%, respectively (form Table 2). The removal mechanismswere complicated and relevant with multiple factors, like soil pH,the oxidability of oxidants, and the migration of pollutants.

Firstly, soil pH is the key factor in affecting the migration ofheavy metals during EK remediation. Many studies indicated that

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HPC

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pyr

ene

conc

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tion

(C/C

0)Exp-01Exp-02Exp-03Exp-04Exp-05

Fig. 3. HPCD-extracted soil pyrene concentration after treatments (C0 = 337.2mg kg�1).

2330 L. Cang et al. / Chemosphere 90 (2013) 2326–2331

heavy metals were accumulated in soil near cathode for the highsoil pH (Reddy and Ala, 2006; Maturi and Reddy, 2008; Maturiet al., 2009). Zhou et al. (2004) achieved 81% removal of soil Cuby conditioning the pH of catholyte during EK remediation of aCu-contaminated soil. Many other studies confirmed this conclu-sion (Zhou et al., 2005; Gidarakos and Giannis, 2006). In our study,the soil pH values ranged from 1.86 to 3.50 in Exp-02 and -05 asconditioning catholyte pH was kept at 3.5. After EK remediation,the Cu removal percents were 69% and 94% in Exp-02 and -05,respectively. On the other hand, soil pH affected the removal of or-ganic pollutants. The results of Saichek and Reddy (2003) indicatedthat the high pH increased phenanthrene solubilization and theamount of EOF, which was conducive to the phenanthrene migra-tion in soil sections from anode to cathode.

Secondly, the migration of pollutants and oxidants are veryimportant to the removal of pollutant from soil columns. Most ofheavy metal ions (Cu2+, Zn2+, Cd2+, Pb2+, Mn2+, and so on) are usu-ally positive-charged and easily moved to cathode by electromigra-tion under DC electric field. However, the migration of organic

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Fig. 4. Percent of different soil Cu fractionations after treatments (F1: acid

pollutants was affected by the kinds of cosolvents, EOF and thekind of oxidants during EK remediation (Acar and Alshawabkeh,1993; Maturi and Reddy, 2008). From Fig. 1b, the amounts ofEOF in Exp-03, -04 and -05 were higher than those in Exp-01 and-02, which was in favour of the migration of pyrene in soil. Mean-while, the NaClO, KMnO4 and Na2S2O8 solution were added intothe catholyte, and the ClO�, MnO�4 and S2O2�

8 were moved to anodeunder DC electric field. The nice migration ability and propermigration direction of organic pollutants and oxidants were condu-cive to the removal of pollutants.

Thirdly, the stability and oxidability of oxidants are one ofimportant factors for the removal of organic pollutants. Amongthe four oxidants in this study, H2O2 and NaClO are easily decom-posed and instable under light and room temperature. KMnO4 andNa2S2O8 are relatively stable and highly soluble, which is condu-cive to the migration of oxidants and the oxidation of organic pol-lutants (Thepsithar and Roberts, 2006). Comparing the oxidabilityof the four oxidants, the standard redox potentials of H2O2, NaClO,KMnO4 and Na2S2O8 are 0.68, 0.89, 1.51 and 2.01 V, respectively.The oxidability of KMnO4 and Na2S2O8 are stronger than those ofH2O2 and NaClO. Therefore, the removal percents of pyrene werehigher in the treatment of KMnO4 and Na2S2O8 than those in thetreatment of H2O2 and NaClO (Table 2).

The last factor affecting the removal percent of compound pol-lutants might be the interaction among the pollutants, the oxi-dants, and their decomposition products, which was generallyneglected by previous studies about EK remediation of heavy met-als–organic compound contaminated soil. In previous studies, hea-vy metals were accumulated in the soil section near cathode forthe high soil pH (Maturi et al., 2009). However, in this study, theCu was accumulated in S5 (soil pH = 3.0) with Cu concentrationof 2057 mg kg�1 in Exp-04. Therefore, soil pH was not the reasonof Cu accumulation in S5 here. Siegrist et al. (2002) found thereduction product MnO2 of KMnO4 would increase the adsorptionpotential of heavy metals during in situ chemical oxidation. In ourstudy, Cu may be adsorbed by the reduction product MnO2 and toform the oxide combination state. From Fig. 4, the Fe–Mn oxidebound fractionation (F2) of Cu in S5 increased significantly, whichfurther demonstrated that Cu formed the oxide combination state

2 S3 S4 S5 S1 S2 S3 S4 S5 S1 S2 S3 S4 S5

Exp-03 Exp-04 Exp-05

tments

F4F3F2F1

soluble, F2: Fe–Mn oxide bound, F3: organically bound, F4: residual).

L. Cang et al. / Chemosphere 90 (2013) 2326–2331 2331

and was accumulated in S5. Thus, the interaction among the pollu-tants, the oxidants, and their decomposition products were consid-ered during the enhanced EK remediation of heavy metals–organiccompound contaminated soil.

4. Conclusions

This study developed a new EK remediation technology to decon-taminate the heavy metal–organic compound co-contaminated soilby addition of different oxidants and controlling electrolyte pH. Theremoval percents of soil pyrene and Cu were 30–52% and 8–94%,respectively. Acidic soil condition is advantageous for the migrationof Cu. KMnO4 is the best oxidants for the degradation of pyreneamong all the oxidants, but it prevented the migration of Cu byforming oxide combination state. Adding Na2S2O8 and controllingcatholyte pH at 3.5 were the best operating conditions for decon-taminating the heavy metals–organic compound co-contaminatedsoil. During oxidants-enhanced EK remediation, the removal ofheavy metals and organic pollutants was affected by soil pH, themigration of pollutants and oxidants, the oxidability of oxidants,and the interaction of various factors.

Acknowledgements

This work was supported by the National Natural ScienceFoundation of China (21177135, 21077111) and the InternationalResearch Staff Exchange Scheme – ELECTROACROSS (269289).

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