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Remediation of Cu-contaminated soil using chelant andEAOPMaja Pociecha a , Helena Sircelj a & Domen Lestan aa Agronomy Department, Biotechnical Faculty , University of Ljubljana , Ljubljana, SloveniaPublished online: 03 Aug 2009.

To cite this article: Maja Pociecha , Helena Sircelj & Domen Lestan (2009) Remediation of Cu-contaminated soil using chelantand EAOP, Journal of Environmental Science and Health, Part A: Toxic/Hazardous Substances and Environmental Engineering,44:11, 1136-1143, DOI: 10.1080/10934520903005160

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Journal of Environmental Science and Health Part A (2009) 44, 1136–1143Copyright C© Taylor & Francis Group, LLCISSN: 1093-4529 (Print); 1532-4117 (Online)DOI: 10.1080/10934520903005160

Remediation of Cu-contaminated soil using chelantand EAOP

MAJA POCIECHA, HELENA SIRCELJ and DOMEN LESTAN

Agronomy Department, Biotechnical Faculty, University of Ljubljana, Ljubljana, Slovenia

An electrochemical advanced oxidation process (EAOP) was used for treatment of the washing solution obtained during leachingof Cu (364 ± 2 mg kg−1) contaminated soil, with chelant S,S isomer of ethylenediamine disuccinate ([S,S]-EDDS). In the EAOP(constant current density 40 mA cm−2), a boron-doped diamond anode was used for the generation of hydroxyl radicals and oxidativedecomposition of [S,S]-EDDS-metal complexes in the washing solution. The released Cu was mostly electro-deposited on the stainless-steel cathode. Three consecutive additions of 5 mmol kg−1 [S,S]-EDDS removed 46% of the Cu from the soil, mostly from carbonateand oxide soil fractions (87 and 99% Cu reduction). The soil Cu oral availability in the simulated stomach and intestinal phases(in vitro physiologically based extraction test) was reduced by 5.5 and 4.6-times. Cu plant availability (in vitro diethylenetriaminepentaacetate test) was reduced by 3.6-times. The discharge solution was clear, almost colorless, with pH 8.4, 0.45 mg L−1 Cu and 0.01mM EDDS.

Keywords: Cu, soil remediation, [S,S]-EDDS, EDTA, EAOP.

Introduction

Contamination with Cu is a major problem of vine-yard soils to which Bordeaux broth and other Cu basedfungicides have been applied for decades. Other releasesof Cu into the land include tailings and overburdensfrom copper mines and the application of sewage sludges.Cu is an essential element for organisms, but high Cuconcentrations in soils are toxic and cause low plantbiomass, delay in flowering and fruiting, and low seedset.[1]

Since more and more contaminated land is expected tobe used for agricultural production and environmental reg-ulation is being more strictly implemented, there is a needto develop effective soil remediation methods. Soil washing(extraction or leaching) with acids and chelants could be aviable option. In soil leaching, the washing solution is grav-itationally percolated through the soil, so the method is notsuitable for soils with low hydraulic permeability. On theother hand, soil leaching, unlike extraction, preserves thesoil structure. Acids dissolve carbonates and other heavymetal bearing soil fractions and exchange heavy metalsfrom soil colloids. Since acidic solutions can cause deteri-

Address correspondence to Domen Lestan, Biotechnical Fac-ulty, University of Ljubljana, Jamnikarjeva 101, 1000 Ljubljana,Slovenia. E-mail: domen.lestan@bf.uni-lj.si

oration of soil biological and physicochemical properties,using chelants is generally considered to be environmen-tally less disturbing.

Chelants form coordinate chemical bonds with met-als (complexes) and facilitate their solubilization from thesoil into a washing solution. Ethylenediaminetetraacetate(EDTA) has been the chelant most often proposed andtested for soil washing, since it forms strong complexes withmost polluting heavy metals.[2] However, for remediation ofCu contaminated soil, the [S,S] isomer of ethylenediaminedisuccinate ([S,S]-EDDS) has been reported to be superiorto EDTA.[3] [S,S] EDDS was first isolated as a metabolite ofthe soil actinomycete Amycolatopsis orientalis and is there-fore naturally present in soil.[4] It was originally developedfor application in laundry detergents. Since it is non-toxicand biodegradable in lower concentrations,[5] it is expectedto replace toxic and environmentally persistent EDTAin commercial applications, despite its current higherprice.

The main problem of current chelant based soil washingtechnologies is the separation of chelant-heavy metalcomplexes from the waste washing solution, before it canbe safely discharged. Although [S,S]-EDDS is biodegrad-able, the removal of heavy metals after biodegradation ofchelate is not feasible, since relatively high [S,S]-EDDSconcentrations in washing solutions prevent sufficientlyfast and efficient biodegradation of the chelant.[6] Further-more, Vandevivere et al.[7] reported that [S,S]-EDDS-Cu

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Remediation of Cu-contaminated soil 1137

complexes are biologically considerably more persistentthan complexes with other heavy metals.

For efficient chelant-based soil leaching, we recently in-troduced a two-phase remediation method using an elec-trochemical advanced oxidation process (EAOP).[8] In thefirst (soil leaching) phase, the soil heap or column isleached with chelant until the optimal (equilibrium) heavymetal removal rate is achieved. In the second (soil-rinsing)phase, the soil washing solution is treated with EAOP tooxidize the chelant with hydroxyl radicals (OH), whileheavy metals are removed by electroparticipation on acathode or are filtrated as insoluble (hydr)oxides. Thecleansed washing solution is then reused in a closed pro-cess loop for soil rinsing to remove all soil retained chelates(Fig.1).

In EAOP, the anode material is the most importantparameter, since molecular oxygen is mainly producedduring water electrolysis if the oxygen overvoltage isnot sufficiently high. We therefore used a recently devel-oped boron-doped diamond anode (BDDA), which en-ables effective OH production directly from the electrol-ysed water.[9] BDDA has an extreme oxygen overvoltage(>3 V) before O2 forms.[10] The novel method was testedwith EDTA as chelant, and Pb, Zn and Cd contaminatedsoil.[8]

In this study, the two-phase soil leaching method us-ing EAOP was further evaluated for Cu contaminated soiland [S,S]-EDDS. Before the bench-scale remediation ex-periment, we compared the efficiency of [S,S]-EDDS toother chelants for Cu removal from soil and optimized theleaching time in small-scale experiments. We also optimizedcurrent density for the washing solution EAOP treatment.In order to evaluate remediation efficiency, the percentageof Cu removed from the soil, as well as chemical (sequen-tial extractions), oral and plant availability of residual Cuin the soil after remediation, were determined.

1

Metalcont.soil

Chelantoxidation

Chelant

Metal(electro-deposited)

Filter Metal(precipitated)

21

Metalcont.soil

Chelantoxidation

Chelant

Metal(electro-deposited)

Filter Metal(precipitated)

2

Fig. 1. Scheme of the two-phase, chelant-based soil leachingmethod with treatment and reuse of the washing solution in aclosed process loop. (1) Soil leaching with chelant; (2) the wash-ing solution treatment, soil rinsing phase.

Table 1. Selected properties of contaminated soil and Cu con-centration and fractionation before and after remediation.

Before AfterSoil properties remediation remediation

pH (CaCl2) 7.3 /Organic matter (%) 6.7 /CEC (mmol C+ 100 g−1) 29.3 /Sand (%) 12.2 /Silt (%) 50.2 /Clay (%) 37.6 /Texture silty clay loam /Total Cu (mg kg−1) a364 ± 2 b195 ± 22PBET test (mg kg−1)Stomach phase a67 ± 2 b12 ± 2Intestinal phase a79 ± 3 b17 ± 2DTPA testDTPA extract (mg kg−1) a83 ± 1 b23 ± 1Cu fractionation (mg kg−1)In soil solution a1.7 ± 0.2 b4.6 ± 0.2Exchangeable a2.8 ± 0.1 b2.4 ± 0.0Bound to carbonate a38 ± 1 b4.8 ± 0.1Bound to Fe and Mn oxides a99 ± 4 b0.7 ± 0.2Bound to organic matter a109 ± 6 b74 ± 1Residual fractionation a114 ± 3 b94 ± 3Recovery (%) 100 ± 1 92 ± 1

Indicated standard deviation from the mean value (n = 3) was cal-culated. Means followed by the same letters are not significantlydifferent according to the Duncan test (P < 0.05).

Materials and methods

Soil properties

Cu contaminated soil was collected from the 0–45 cm sur-face layer of a vineyard (x = 040370 m and y = 400570 m,Gauss-Kruger coordinate system). Soil pH was measuredin a 1/2.5 (w/v) ratio of soil and 0.01 M CaCl2 water so-lution suspension. Soil samples were analyzed for organicmatter by Walkley-Black titrations, cation exchange capac-ity by ammonium acetate and the Melich method and soiltexture by the pipette method (Table 1).

Optimization of the remediation process parameters

In small-scale leaching experiments, soil (150 g) was placedin perforated 250 mL polypropylene flasks with a 0.5 mmplastic mesh at the bottom to retain the soil. Soil wasleached in triplicate with a 100 mL washing solution con-taining 5, 10 and 15 mmol kg−1 EDTA disodium salt, [S,S]-EDDS and diethylenetriamine pentaacetate (DTPA). Thewashing solution leached from the soil was collected andre-applied on top of the soil with a peristaltic pump (flowrate 2 mL min−1) for 24 h. In an additional experiment,soil was leached with single, double and triple doses of 5,10 and 15 mmol kg−1 [S,S]-EDDS. After leaching (after

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1138 Pociecha et al.

each dose), the soil was rinsed with 2 L of tap water to re-move all measurable mobile Cu species. We checked this bymeasuring the Cu concentrations in the rinsing solutions(data not shown). At the end, the washing and rinsing solu-tions were combined. The volume and Cu concentration inthe combined solution were measured and used to calculatethe percentage of Cu removed from the soil.

In experiments in which the effect of [S,S]-EDDS contacttime on Cu removal was studied, the washing solution (10mmol kg−1 [S,S]-EDDS circulated through the soil for 240h, and the concentration of Cu in the washing solution wasperiodically measured in order to calculate the percentageof Cu removed from the soil.

Electrolytic cell

The electrolytic cell consisted of a BDD anode (Diachem,Condias GmbH, Itzehoe, Germany) and two stainless steelcathodes, with an electrode distance of 4.5 mm. The BDDAhad a Ti base coated with a conductive polycrystalline dia-mond layer (the conductivity of the electrode was regulatedby the addition of boron). The overall BBD anode surfacewas 100 cm2. The surface area ratio between the cathodesand anode was 1:2. Current densities were adjusted (from15 to 40 mA cm−2) and cell voltage measured with a DCpower supply (Elektronik Invent, Ljubljana, Slovenia). Itwas ensured that the flow of soil washing solution was onlythrough the space between the anode and cathodes. Theelectrode cell was cooled using a cooling mantle and tapwater to keep the temperature of the treated washing solu-tion below 35◦C.

EAOP treatment of [S,S]-EDDS-Cu soil washing solution

In order to obtain the washing solution, we placed 4.5 kgof air-dried soil in 15 cm diameter soil columns (three repli-cates) and leached the soil with a 4600 mL aqueous solutionof 10 mmol kg−1 [S,S]-EDDS for 48 h. Approximately 2500mL of the washing solution per column was collected.

To test the feasibility of using BDDA EAOP for treat-ment of the soil washing solution, we circulated 500 mL ofsoil washing solution from a 1-L Erlenmeyer flask throughthe electrode cell (peristaltic pump, flow rate 90 mL min−1).Current densities used were 15, 25 and 40 mA cm−2. Sam-ples (30 mL) of washing solution were collected at intervalsfrom 10 to 60 min of contact time in the electrode cell.Contact time was calculated as the ratio of the electrodecell volume to the volume of washing solution and multi-plied by the operation time (initially 44 min of operationtime equalled 10 minutes of contact time). Samples werefiltrated (filter paper grade 391, 84 g m−2), the pH and ECmeasured, and the samples stored in the cold for furtheranalysis of Cu and [S,S]-EDDS concentrations.

The cathodes were rinsed with 10 mL 37% HNO3 todissolve deposited Cu and the concentration of Cu was an-alyzed (AAS) to determine the percentage of Cu that had

been removed from the washing solution by electrodepo-sition. The percentage of Cu removed from the washingsolution by filtration was then calculated.

The specific energy consumption (SEC) was calculatedusing Equation 1:

SEC = (U × I × t)/m (1)

where U is the voltage measured during the treatment (inV), I the applied electrical current (in A), t the operationtime (in h) and m the amount of pollutant (Cu) removedfrom the solution (in g). SEC was expressed in kWh g−1.

Bench-scale remediation of contaminated soil

A two-phase soil remediation method (Fig. 1) with threeconsecutive [S,S]-EDDS additions was simulated in a bench(laboratory) scale experiment. Air-dried soil (4.5 kg) wassieved (5 mm mesh) and placed in a 15 cm diameter col-umn 23.5 cm high. Plastic mesh (0.2 mm) at the bottomof the column retained the soil. The initial soil washingsolution contained 5.0 mmol kg−1 [S,S]-EDDS in 3 L un-buffered tap water (this volume was 145% of the soil wa-ter holding capacity). The washing solution was circulatedin the first (leaching) phase (peristaltic pump, flow rate15 ml min−1) solely through the soil for 48 h. In the second(rinsing) phase, the washing solution circulated throughthe soil, electrode cell (current density 40 mA cm−2) and3 filters. HEPA-quality cooker-hood material availablefrom a local home appliances store was used as filteringmaterial.

Thirty mL samples of washing solution were collectedfrom the column outlet after each 10 min of contact timein the electrode cell (10 minutes of contact time equaled 4h and 42 min of operation time) and pH, EC, Cu and [S,S]-EDDS concentrations were determined. When the concen-tration of Cu in the treated washing solution fell below10 mg L−1, a fresh 5 mmol kg−1 [S,S]-EDDS was added tothe washing solution (second chelant addition) with 0.75 Lof tap water to compensate for water lost during the pro-cess (sampling, evaporation, electrolysis). Again, the wash-ing solution was sampled every 10 min of contact time andwhen the Cu concentration fell below 10 mg L−1, a third,last dose of 5 mmol kg−1 [S,S]-EDDS was added with 0.75L of tap water. After the last chelant addition, the rinsingphase was prolonged to obtain a discharge solution withsufficiently low heavy metal and [S,S]-EDDS concentra-tions. The soil column was dismantled and samples weretaken from different soil layers (profile) for further deter-mination of residual Cu.

Cu oral bioavailability

Cu oral bioavailability before and after soil remediationwas determined using an in vitro Physiologically Based Ex-traction Test (PBET) according to Turner and Ip. [11] In thefirst phase of the test, 0.5 g of sieved soil sample (250 µm)

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Remediation of Cu-contaminated soil 1139

was digested in a reaction flask for 2 h at constant temper-ature (37◦C) in simulated gastric fluid (50 mL) prepared bydiluting 1.25 g pepsin (porcine, Sigma), 0.50 g citrate, 0.50 gmalate, 420 µL lactic acid and 500 µL acetic acid in 1 Ldeionized water and adjusting the pH to 2.50 ± 0.05 withdiluted HCl. The pH of the reaction mixture was measuredevery 10 min and adjusted with HCl as necessary to keepit at a value of 2.50 ± 0.05. Samples (5 mL each) were col-lected after 2 h and centrifuged at 2500 g min−1 for 25 min.The liquid fraction was decanted for further analysis.

The 5 mL sample volume was replaced with gastric so-lution to maintain a constant volume in the reaction flask.After 2 h, the second phase of the test began by titratingthe reaction to pH 7.00 with saturated NaHCO3 solution.When the reaction vessel reached equilibrium at pH 7, 175mg of bile salts (porcine, Sigma) and 50 mg of pancre-atin (porcine, Sigma) were added, thus simulating smallintestine conditions. After 2 h, the reaction solutions werecentrifuged at 2500 g min−1 for 25 min. The liquid fractionwas decanted and analyzed as the small intestine fraction.During both phases, a constant moistened argon flow (1L min−1) at 37◦C passed through the reaction mixture inorder to simulate peristalsis. Three PBET extractions wereperformed for each sample.

Cu plant availability

Cu plant availability before and after soil remediation wasdetermined using an in vitro DTPA test according to Lind-say and Norwell.[12] The DTPA extraction solution wasprepared containing 0.005 M DTPA, 0.01 M CaCl2, and0.1 M triethanolamine (TEA). The pH was adjusted to 7.30± 0.05. 5 g of soil sample, which was sieved to 2 mm, shakenin 10 ml of DTPA extracting solution for 2 h on a horizon-tal shaker at 120 cycles min−1. After the extraction period,the contents were filtered (Whatman No. 42 filter paper)and the filtrates analyzed for Cu. Three DTPA extractionswere performed for each sample.

Cu fractionation

The Tessier et al.[13] sequential extraction procedure, mod-ified by Lestan et al.[14] was used to determine the fraction-ation of Cu in non-remediated and remediated soil into 6fractions: soluble in soil solution, exchangeable from soilcolloids, bound to carbonates, bound to Fe and Mn oxides,bound to organic matter and the residual fraction soluble inaqua regia. Three determinations of Cu concentration weremade for each fractionation sequence. The final fractionalrecovery of Cu was calculated after summing the recoveriesof all 6 steps of sequential extraction.

[S,S]-EDDS determination

Samples of washing and soil rinsing solution were filtrated(filter paper grade 391, 84 g m−2) and [S,S]-EDDS deter-

mined using the procedure described by Tandy et al.[15]. Avolume of 0.4 ml of EDTA buffer (pH 11.5) was added to1.6 ml of the sample and then heated for 3 h at 90◦C, cooled,then 1.0 ml of 9-fluorenyl-methyl chloroformate (FMOC)reagent was added and allowed to react for 30 min at roomtemperature. Four ml of dichloromethane were added, thesample was shaken and centrifuged. Extracts were thenanalysed with the Spectra-Physics HPLC system, on an Ul-trasphere column ODS C-18, 5 µm, 250 × 4.6 mm, using afluorescence detector (excitation 260 nm, emission 310 nm).The mobile phase consisted of 0.05 M NaH2PO4/ 0.05 MNa2HPO4 with a pH of 6.8. The following gradient elutionwas used: 0–6 min from 10% acetonitrile to 20%, 6–8 minfrom 20 to 80% acetonitrile, 8–11 min at 80%, 11–12 minfrom 80 to 10%, 12–20 min at 10% acetonitrile. The flowrate was 1 ml/min at room temperature.

Cu determination

Air-dried samples of non-leached and leached soil (1 g)were ground in an agate mill, digested in aqua regia (28mL), diluted with deionized water up to 100 mL, andCu analyzed by flame (acetylene/air) AAS with a deu-terium background correction (Varian, AA240FS). The Cuin washing, rinsing and PBET solutions was determined byAAS directly. A standard reference material used in inter-laboratory comparisons (Wepal 2004.2.2) was used in thedigestion and analysis as part of the QA/QC protocol. Therecovery percentage for Cu was 100 ± 3. Reagent blank andanalytical duplicates were also used where appropriate, inorder to ensure accuracy and precision in the analysis.

Statistics

The Duncan multiple range test was used to determine thestatistical significance (P < 0.05) between different treat-ments, using the computer program Statgraphics 4.0 forWindows.

Results and discussion

Optimization of the remediation process parameters

We used small-scale leaching experiments (150 g of soil) toprovide process parameters for the bench-scale remediationexperiment. We first tested the efficiency of three differentchelants for Cu removal from the soil. [S,S]-EDDS provedto be significantly more effective than EDTA in all con-centrations tested (Fig. 2). The superiority of [S,S]-EDDSfor Cu removal over EDTA and other chelants was alsoreported earlier by Tandy et al.[3] and Kos and Lestan.[16]

DTPA was fairly ineffective (Fig. 2). While the percentageof removed Cu increased with increasing EDTA concentra-tion, this increase was minor (and statistically not signifi-cant) with higher [S,S]-EDDS dosages (Fig. 2). Presumably

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Fig. 2. Removal of soil Cu after soil leaching (small-scale ex-periment) using three different concentrations of three differentligands. Error bars represent standard deviation from the meanvalue (n = 3).

5 mmol kg−1 [S,S]-EDDS was sufficient to remove a ma-jority of the Cu chemically available from soil to chelant.In this chelant concentration, the molar ratio of chelant tosoil Cu was 0.9:1.

Finzgar and Lestan,[17] and Udovic and Lestan[18] re-ported that multiple-dosages of EDTA were substantiallymore effective for leaching Pb, Zn, Cd and Cu from con-taminated soils than using one large single dose. Similarly,three-dosages of 5 mmol kg−1 [S,S]-EDDS removed sig-nificantly more Cu than one single dose of 15 mmol kg−1

[S,S]-EDDS (Fig. 3). Nevertheless, the second and third[S,S]-EDDS dosages were less efficient than the first (Fig. 3),since more easily extractable Cu species were already re-moved from the soil with the first dose of chelant, as men-tioned above. We chose to use 5 mmol kg−1 [S,S]-EDDSin further experiments and three consecutive dosages ofchelant in the bench-scale remediation experiment.

As shown in Figure 4, the efficiency of [S,S]-EDDS re-moval of Cu increased with the contact time up to 48 h andafterwards slightly fluctuated. The Cu removal efficiency

60

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Concentration of [S,S] EDDS (mmol kg-1)

Cu

rem

ove

d (

%)

60

0

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Concentration of [S,S] EDDS (mmol kg-1)

Cu

rem

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%)

Fig. 3. Cu removal after soil leaching (small-scale experiment)using three different [S,S]-EDDS concentrations in single andmultiple dosages. Error bars represent standard deviation fromthe mean value (n = 3).

0

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0 50 100 150 200 250

Time (h)

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(m

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Time (h)

Cu

(m

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Cu

(m

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Fig. 4. Concentration of Cu in the washing solution after soilleaching (small-scale experiments) with 10 mmol kg−1 [S,S]-EDDS using different reaction times. Error bars represent stan-dard deviation from the mean value (n = 3).

after 10 days (240 h) extraction decreased, most likely dueto slow microbiological degradation of the [S,S]-EDDS-Cucomplex[5,7] and binding of the released Cu back to thesoil solid phase. We allowed a 48 h reaction time in thebench-scale remediation experiment.

EAOP treatment of [S,S]-EDDS-Cu soil washing solution

The concentration of Cu in the soil washing solution beforetreatment in the electrolytic cell was 221 ± 10 mg L−1. Theinitial [S,S]-EDDS concentration was 3016 ± 712 mg L−1

(8.4 ± 2.0 mM) and the pH of the washing solution was8.0 ± 0.2. Figure 5 shows that the EAOP using BDDAefficiently removed Cu and [S,S]-EDDS from the washingsolution. After 60 min contact time, 94%, 86% and 71%of Cu was removed using 40, 25 and 15 mA cm−2 currentdensities, respectively. [S,S]-EDDS was almost completelyremoved at all current densities. The voltage slightly de-creased during the treatment (from 8.6 ± 0.7 to 7.3 ± 0.6V, from 10.1 ± 0.4 to 9.3 ± 0.3 V, and from 14.0 ± 0.9 to11.7 ± 0.3 V for current densities 15, 25 and 40 mA cm−2,respectively). The pH of the washing solution slightly in-creased from 8.1 ± 0.1 up to 8.7 ± 0.3 during the treatmentwith 40 mA cm−2. The electrical conductivity in the soilwashing solutions fluctuated during the EAOP treatmentbetween 2630 µS cm−1 and 3950 µS cm−1.

Cu was removed from the washing solution as an elec-trodeposit on the cathode or by filtration. Most of the totalremoved Cu was removed by electrodeposition: 90, 87 and76% for 15, 25 and 40 mA cm−2 treatments, respectively.The electrodeposited Cu was removed from the cathodeby etching with nitric acid and the Cu concentration (con-tent) measured. The remaining Cu was precipitated fromthe treated washing solution and was easily removed by fil-tration (the content of precipitated Cu was not measured).

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Remediation of Cu-contaminated soil 1141

-2

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DS

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Fig. 5. Effect of current density on Cu and [S,S]-EDDS removalfrom the washing solution using BDDA EAOP. Error bars repre-sent standard deviation from the mean value (n = 3).

The Cu probably precipitated as metal hydroxide, formedclose to the cathode, where a higher pH is expected dueto the formation of OH− during water electrolysis.[19] An-other possible mechanism is the anodic oxidation of metalsby hydroxyl radicals.[20] Alkalinisation, and probably alsoanodic oxidation, were more explicit at higher current den-sities, which presumably explains the lower percentages ofelectrodeposited Cu.

The operating cost of EAOP treatment of soil washingsolution is directly related to the specific energy consump-tion (SEC). SEC is defined as the amount of electrical en-ergy consumed per unit mass of pollutant (Cu in the presentcase) removed. The SEC increased with the current densi-ties applied: 0.64, 1.06 and 1.98 kWh g−1 for treatmentswith 15, 25 and 40 mA cm−2, respectively, were calculated.Some of the energy lost at higher current densities waspresumably due to heating of the treated solution.

As shown in Figure 5, [S,S]-EDDS degradation and Curemoval were faster at higher current densities. We thereforeused a current density of 40 mA cm−2 for the bench-scaleremediation experiment. There are no other literature dataon using EAOP for treatment of wastewaters containing[S,S]-EDDS or its salts.

Bench-scale remediation of Cu contaminated soil

In a laboratory, bench-scale simulation of a two-phaseleaching method (Fig. 1), the concentrations of Cu in the

washing solution (measured immediately after the leachingand before the rinsing phase) was lower after each of thethree [S,S]-EDDS doses (Fig. 6, time = 0 min.) as less andless Cu chemically available to the chelant remained in thesoil. The reduction of Cu (electrodeposition and filtrationof Cu participates) and [S,S]-EDDS (oxidative degrada-tion) in the washing solution during the three soil rinsingphases when the washing solution was treated by BDDAEAOP is presented in Figure 6. At a constant current den-sity of 40 mA cm−2, the voltage in the electrolytic cell de-creased from an initial 18.2 to 13.4 V towards the end ofthe remediation, as electric conductivity in the soil washingsolution increased from an initial 1870 to 2050 µS cm−1.During the rinsing phases, the discharge solution graduallylost its initial intensive green color and, at the end of theremediation, was clear, almost colorless and slightly basic(pH 8.4). The concentrations of Cu (0.45 mg L−1) and [S,S]-EDDS (2.1 mg L−1) were quite low (Fig. 6) and the finalsolution was ready to discharge or reuse without furtherpurification.

After remediation, 46% of Cu was removed from thesoil. This is somewhat lower than in the small-scale exper-iments in which soil was leached in the same way (3 ×5 mmol kg−1 [S,S]-EDDS) and in which 55% of Cu wasremoved. Presumably, in the bench-scale experiment, partof the Cu precipitates in the washing solution were smallenough to pass through the filtering system. This lost Cuthen re-contaminated the upper two soil layers, in whichwe measured significantly higher (P < 0.05) Cu concentra-tions than in the bottom layer (Fig. 7). This was difficult toavoid in a laboratory experiment, in which separation meth-ods other than filtration were not practical. However, in alarge-scale process it would be less of a technical problem,especially in combination with other separation processessuch as flotation or sedimentation.

The reason for relatively poor Cu removal (in additionto problems with filtering fine Cu particles) was the spe-cific Cu fractionation profile (Table 1). Most of the Cu wasbound to the residual fraction (48%) of the sequential ex-traction and to soil organic matter (38%). Metals bound tothese (last) fractions of the sequential extraction scheme areconsidered to be poorly extractable and biologically avail-able, and therefore also less toxic. Remediation removedthe more easily available and more toxic Cu from the car-bonate fraction (87% reduction) and the fraction of soiloxides (99% reduction).

That the Cu left in the soil after remediation was in sig-nificantly less toxic forms was also indicated by data onCu oral bio-availability, assessed by the Turner and Ip[11]

PBET test, designed to simulate stomach and intestinalphases of the human gastrointestinal tract. After remedia-tion, the concentration of Cu available from (ingested) soilin the stomach phase was reduced by 82% and from theintestinal phase by 78% (Table 1). The logical goal for re-mediation of a vineyard soil would also be the reduction ofCu availability to plants, particularly to vine. Since vine is a

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Fig. 6. Concentrations of Cu and [S,S]-EDDS in the washing solution during two-phase soil remediation using BDDA EAOP. Soilwas remediated with three consecutive dosages (I, II, III.) of 5 mmol kg−1 [S,S]-EDDS.

fairly slow growing plant, we chose to use an in vitro test toassess metal plant-availability. The Lindsay and Norwell[12]

DTPA-based test is the most commonly used and data in-dicated that, after remediation, Cu plant – availability wasreduced by 72% (Table 1).

An accurate evaluation of the costs associated with atwo-phase BDDA EAOP soil remediation method wouldrequire a pilot-scale experiment (after further process opti-mization). However, [S,S]-EDDS and electricity consump-tion (which presumably represent the major part of thetotal costs) can be extrapolated from our bench-scale ex-periment. Leaching 1 ton of soil would require 5.37 kg of

[S,S]-EDDS. At a current price of approx. 6 € per kg−1

[S,S]-EDDS for the technical-grade chemical from a ma-jor European manufacturer this translates into 32.22 €.Treatment of the washing solution (without appropriatescale-up of the equipment) would require 17525 h at a con-stant current of 4 A and average voltage 13.6 V. This is953.4 kWh and at an approx. cost 0.1 € per KWh trans-lates into 95.34 €. The approx. [S,S]-EDDS and electric-ity costs would therefore be 128 € ton−1 (166 € m−3) ofsoil. This is not the total cost, but nevertheless seems rea-sonable. The current cost of soil washing can go up to450 € per m−3.[21]

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Fig. 7. Cu concentration through the soil profile in the soil col-umn before (dotted line) and after (solid line) heap leaching withthree dosages of 5 mmol kg−1 [S,S]-EDDS. Error bars representstandard deviation from the mean value (n = 3). Means followedby the same letters are not significantly different, according to theDuncan test (P < 0.05).

Conclusions

The use of EAOP and BDDA for oxidative degradationof chelant and removal of Cu from the washing solution(by electrodeposition and participation) during two-phasesoil leaching with [S,S]-EDDS, is feasible. Soil leaching re-moved only half of the total Cu from the soil, mostly dueto fractionation of the Cu into non-labile soil fractions,whereby Cu was not easily accessible to the chelant. Never-theless, a significant part of the potentially chemically, bio-and phyto-available Cu was removed from the soil by reme-diation (Cu bio-stripping). The final washing solution wasalmost free of Cu and [S,S]-EDDS and safe for discharge.

Acknowledgments

This work was supported by the Slovenian Ministry for Ed-ucation, Science and Sport, Grant J4-6134-0481-04/4.03.

References

[1] Brun, L.A.; Maillet, J.; Hisinger, P.; Pepin, M. Evaluation of copperavailability to plants in copper-contaminated vineyard soils. Envi-ron. Pollut. 2001, 111, 293–302.

[2] Kim, C.; Lee, Y.; Ong, S.K. Factors affecting EDTA extrac-tion of lead from lead-contaminated soils. Chemosphere 2003, 51,845–853.

[3] Tandy, S.; Bossart, K.; Mueller, R.; Ritschel, J.; Hauser, L.; Schulin,R.; Nowack, B. Extraction of heavy metals from soils usingbiodegradable chelating agents. Environ. Sci. Technol. 2004, 38,937–944.

[4] Nishikiori, T.; Okuyama, T.; Naganawa, T.; Takita, T.; Hamida,M.; Takeuchi, T.; Aoyagi, T.; Umezawa, H. Production of acti-nomycetes of (S,S)-N, N′-ethylenediamine-disuccinic acid, an in-hibitor of phospholipase. C. J. Antibiot. 1984, 37, 426–427.

[5] Jaworska, J.S.; Schowanek, D.; Feijtel, T.C.J. Environmental riskassessment for trisodium [S,S]-ethylene diamine disuccinate, abiodegradable chelator used in detergent application. Chemosphere1999, 38, 3597–3625.

[6] Finzgar, N.; Zumer, A.; Lestan, D. Heap leaching of Cu contam-inated soil using [S,S]-EDDS in a closed process loop. J. Hazard.Mater. 2006, 135, 418–422.

[7] Vandevivere, P.; Hammes, F.; Verstreate, W.; Feijetel, T.; Schowanek,D.J. Metal decontamination of soil, sediment, and sewage sludge bymeans of transition metal chelant [S,S]-EDDS. J. Environ. Eng.2001, 127, 802–811.

[8] Finzgar, N.; Lestan, D. The two-phase leaching of Pb, Zn and Cdcontaminated soil using EDTA and electrochemical treatment ofthe washing solution. Chemosphere 2008, 73, 1484–1491.

[9] Troster, I.; Schafer, I.; Fryda, M. Recent development in productionand application of DiaChem

©Relectrodes for wastewater treatment.

New Diam. Front. C. Tec. 2002, 12, 89–97.[10] Kraft, A.; Stadelmann, M.; Blaschke, M. Anodic oxidation with

doped diamond electrodes: a new advanced oxidation process. J.Hazard. Mater. 2003, 103, 247–261.

[11] Turner, A.; Ip, K.H. Bioaccessibility of metals in dust from the in-door environment: application of a physiologically based extractiontest. Environ. Sci. Technol. 2007, 41, 7851–7856.

[12] Lindsay, W.L.; Norwell, W.A. Development of a DTPA soil test forzinc, iron, manganese and copper, Soil Sci. Soc. Am. J. 1978, 42,421–428.

[13] Tessier, A.; Campbell, P.G.C.; Bisson, M. Sequential extraction pro-cedure for the speciation of particulate trace metals. Anal. Chem.1979, 51, 844–851.

[14] Lestan, D.; Grcman, H.; Zupan, M.; Bacac, N. Relationship ofsoil properties to fractionation of Pb and Zn in soil and their up-take into Plantago lanceolata. Soil Sediment Contam. 2003, 12,507–522.

[15] Tandy, S.; Schulin, R.; Suter, M.J.-F.; Nowack, B. Determinationof [S,S’]-ethylenediamine disuccinic acid (EDDS) by high perfor-mance liquid chromatography after derivatization with FMOC. J.Chromatogr. A 2005, 1077, 37–43.

[16] Kos, B.; Lestan, D. Chelator induced phytoextraction and in situsoil washing of Cu. Environ. Pollut. 2004, 132, 333–339.

[17] Finzgar, N.; Lestan, D. Multi-step leaching of Pb and Zn contami-nated soils with EDTA, Chemosphere 2007, 66, 824–832.

[18] Udovic, M.; Lestan, D. EDTA leaching of Cu contaminated soilsusing ozone/UV for treatment and reuse of washing solution in aclosed loop. Water Air Soil Pollut. 2007, 181, 319–327.

[19] Zhou, D-M.; Deng, C-F.; Cang, L.; Alshawabkeh, A.N. Electroki-netic remediation of a Cu-Zn contaminated red soil by controllingthe voltage and conditioning catholyte pH. Chemosphere 2005, 61,519–527.

[20] Chitra, S.; Paramasivan, K.; Sinha, P.K.; Lal, K.B. Ultrasonic treat-ment of liquid waste containing EDTA. J. Clean. Prod. 2004, 12,429–435.

[21] Summergill, I.M.; Scott, D.W. Remediation technology costsin the UK & Europe. Proceedings of the 9th InternationalFZK/TNO Conference on Soil-Water Systems, Bordeaux, France,2005. Forschungszentrum Karlsruhe GmbH: Karlsruhe, Germany,2005.

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