The sequential use of washing and an electrochemical reduction process for the remediation of lead-contaminated soils

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  • This article was downloaded by: [New Jersey Institute of Technology]On: 19 August 2014, At: 08:35Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

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    The sequential use of washing and an electrochemicalreduction process for the remediation of lead-contaminated soilsAydeniz Demir a & Nurcan Kleli aa Department of Environmental Engineering , Mersin University , Mersin , TurkeyAccepted author version posted online: 01 Aug 2012.Published online: 06 Sep 2012.

    To cite this article: Aydeniz Demir & Nurcan Kleli (2013) The sequential use of washing and an electrochemicalreduction process for the remediation of lead-contaminated soils, Environmental Technology, 34:6, 799-805, DOI:10.1080/09593330.2012.717107

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  • Environmental Technology, 2013Vol. 34, No. 6, 799805,

    The sequential use of washing and an electrochemical reduction process for the remediation oflead-contaminated soils

    Aydeniz Demir and Nurcan Kleli

    Department of Environmental Engineering, Mersin University, Mersin, Turkey

    (Received 31 January 2012; final version received 26 July 2012 )

    A two-step method for the remediation of three different types of lead (Pb)-contaminated soil was evaluated. The first stepincluded soil washing with ethylenediaminetetraacetic acid (EDTA) to remove Pb from soils. The washing experimentswere performed with 0.05 M Na2EDTA at 1:10 soil to liquid ratio. Following the washing, Pb removal efficiency from soilsranged within 5070%. After the soil washing process, Pb2+ ions in the washing solution were reduced electrochemically ina fixed-bed reactor. Lead removal efficiency with the electrochemical reduction at 2.0 V potential ranged within 5776%.The overall results indicate that this two-step method is an environmentally-friendly and effective technology to remediatePb-contaminated soils, as well as Pb-contaminated wastewater treatment due to the transformation of toxic Pb2+ ions into anon-hazardous metallic form (Pb0).

    Keywords: lead; EDTA; washing; electrochemical reduction; contaminated soil

    1. IntroductionThe lead contamination of soils has become a major con-cern all over the world. Lead can cause very serioushealth problems including damage to the kidneys, the liverand the reproductive system, basic cellular processes andbrain functions [1]. Some physical, chemical and biologi-cal methods have been used for the remediation of heavymetal-contaminated soils. Among thesemethods, the wash-ing technique is the most common one used ex situ orin situ because it demonstrates a very high efficiency forheavy metal removal from both soils and sediments [2].Acids, bases or chelating agents are being used in general inthe soil-washing technique [3]. Ethylenediaminetetraaceticacid (EDTA) is the most widely used chelating agent forsoil washing, since it forms strong complexes with mostpolluting heavy metals and facilitates their solubilizationfrom the soil into the washing solution [46]. It is relativelyinexpensive compared to other chelants [7].

    EDTA increases Pb2+ leaching due to the formation ofhighly soluble Pb2+-EDTA complexes as follows [8]:

    Pbads + Na2EDTA PbEDTA + NaadsPb2+ + EDTA4 PbEDTA2

    The main problem associated with soil washing is thegeneration ofmetal ions in the solution phase (PbEDTA2),which requires a further treatment method to remove suchions from solution.

    Corresponding author. E-mail:

    An alternative and effective process to lower the levelsof soil pollutants is the electrochemical method, which isalso called the electrokineticmethod. The electrochemicalmethod is a process in which a low-voltage direct-currentelectric field is applied across a section of contaminatedsoil to move contaminants. The principle of electroki-netic remediation is similar to a battery. After electrodes(a cathode and anode) are induced and charged, particles(e.g. ions) are mobilized by the electrical field. Ions andwater move toward the electrodes. Since it can work at dif-ferent pH values depending on the characteristics of theelectrodes [9], it has been used abundantly in the treat-ment processes ofmunicipal and industrial wastewater [10].Within the electrochemical method, special attention isgiven to the electrochemical reduction method. The elec-trochemical reduction method is the reduction of metal ionsfrom an electrolyte in an electric field and is synonymouswith electrowinning, electrolytic recovery, electroextrac-tion or electrodeposition [11]. This method is a processwhich has the potential to keep certain heavy metals out ofthe environment [11]. Electrochemical reduction is an alter-nativemethod for safe disposal. This technology is effectivein improving the treatment quality of industrial wastes,wastewaters and drinking waters on integration into a treat-ment plant or replacement of conventional processes thatare found to be less effective for eliminating specific organicand inorganic pollutants. This technique allows a decreasein the amount of metallic sludge produced by generatingcompact and less voluminous sludge, thereby resulting in

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    a cost-saving process [10]. Many researchers use electro-chemical methods for removing heavy metals from soiland wastewater. These studies mainly focus on in situ soiltreatment [1214]. In addition, complexing ligands, suchas EDTA, are also known to increase the electrochemicalremediation of soil [1517].

    Traditionally each soil treatment method such as soilwashing or electrochemical reduction provides only the dis-placement of the pollutants. In this case, only the shape ofpollutants will be changed and pollutants will not beremoved completely. The application of only one of themethods of soil treatment is not adequate, so combined orsequential soil treatment systems, which are more effec-tive, are being developed to remove pollutants. In recentyears, combined treatmentmethods including electrokineticremediation have been studied for the in situ remediationof heavy metal-contaminated soils [4,18,19].

    The main objective of this study is to assessment theapplicability of a sequential or combined use of soilwashingand the electrochemical reduction process to remediate Pb-contaminated soils.

    2. Materials and methods2.1. Soil samples and propertiesThree surface soil samples collected at a depth of 030 cmwere identified as S1, S2 and S3. Two of them (S1 andS2) were collected from a vegetable garden (unpollutedsoils) and the other one (S3) was collected from a site withrecent Pb mining and smelting operations (polluted soil).Samples transported to the laboratory in plastic bags wereair-dried and crushed to pass through a 2mm sieve. Aftermixing thoroughly, they were stored in plastic bags priorto the laboratory analyses. Soil samples were analysed forpH and electrical conductivity in a 1:2 (m:v) ratio of soilto water solution suspension after 1 h of contact time [20],carbonate (CaCO3) contentwasmeasured by a volumetricalcalcimetermethod as describedbyAllison andMoodie [21],particle size analysis by a hydrometric method [22], Atter-berg limits according to ASTM D4318 procedure [23],organic matter (OM) by theWalkleyBlack procedure [24],cation exchange capacity (CEC) by the ammonium acetateprocedure [25], total soil surface area by ethylene glycolmonoethyl ether adsorption (EGME) [26], elemental analy-sis by X-ray fluorescence (XRF) spectrophotometry (modelXRF Rigaku Rix 2000), and for total Pb concentrationsaccording to DIN ISO 11466 [27] using an atomic absorp-tion spectrometer (AAS) (model SENSAA). Controls of theanalytical procedure were performed using blanks and thereferences (CRM 7003 and CRM 483), which are treated inthe sam


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