Pilot-scale washing of metal contaminated garden soil using EDTA

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  • Journal of Hazardous Materials 215 216 (2012) 32 39

    Contents lists available at SciVerse ScienceDirect

    Journal of Hazardous Materials

    j our na l ho me p age: www.elsev ier .com/ locate / jhazmat

    Pilot-scale washing of metal contaminated garde

    David VoAgronomy Dep a, Slov

    a r t i c l

    Article history:Received 7 OcReceived in reAccepted 8 FebAvailable onlin

    Keywords:ContaminatedToxic metalsEDTAPilot scale rem

    with ere

    cetic ly, an

    metaetriam

    usedprocetatedom te pr

    eansist of

    1 of s

    1. Introduction

    Soil cont(PTMs) is ubronmental psites in wesare in needPTMs are thPTMs are pList), in 72%Departmen

    The full-ditionally inPTMs by adto disposalexcavation-viable soludial optionsinvolves eit

    Corresponcal Faculty, UnTel.: +386 01 4

    E-mail add

    physical separation processes, in which PTM contaminated nesare segregated from the relatively uncontaminated bulk;

    0304-3894/$ doi:10.1016/j.amination with potentially toxic metals and metalloidsiquitous in the world and is a serious health and envi-roblem. There are more than 1.8 million contaminated

    tern central and south-eastern Europe, of which 240,000 of remedial treatment. In almost 40% of these sites,e most important contaminants [1]. In the United States,resent in 77% of the Superfund sites (National Priority

    of the Department of Defence Sites and in 55% of thet of Energy sites [2].scale remediation of PTM contaminated sites has tra-volved soil excavation followed by immobilization ofditives, such as cement, phosphates and clays, prior

    of the treated material in a permitted landll. Sincemobilisation-disposal is no longer considered to be ation [3], soil washing remains one of the few reme-

    to remove PTMs permanently from soils. Soil washingher:

    ding author at: Centre for Soil and Environmental Science, Biotechni-iversity of Ljubljana, Jamnikarjeva 101, 1000 Ljubljana, Slovenia.23 1161; fax: +386 01 423 1088.ress: domen.lestan@bf.uni-lj.si (D. Lestan).

    chemical extraction, in which the contaminants are selectivelydissolved;

    a combination of both physical and chemical processes [4].

    Physical separation processes are effective and commercializedfor sandy soils in which clay, silt and organic matter content (par-ticles less than 0.063 mm) is less than 3035% of the soil [4]. Assuch, they are not applicable for gardens soils, which usually havea higher content of nes. Chemical extraction processes, on theother hand, are not constrained by soil texture. They are a two-stage process that involves soil extraction, usually with acids andchelating agents and recovery of the dissolved PTMs from the usedwashing solution. Extraction with acids changes the soil matrix,while chelating agents largely preserve soil properties as a plantsubstrate. Many different chelating agents (mostly aminopolycar-boxylic acids) have been tested for soil washing. Di-sodium salt ofethylenediamine tetraacetate (EDTA) has been the most frequentlyused because of its efciency, availability and relatively low cost[5]. Nevertheless, washing soils with EDTA still poses signicantproblems:

    Washing soils rich with clay and other nes is difcult. Various PTMs, both cationic (e.g., Pb) and anionic (e.g., As), coexist

    in most contaminated soils. A single washing reagent makes itdifcult efciently to remove all of them simultaneously [6].

    see front matter 2012 Elsevier B.V. All rights reserved.jhazmat.2012.02.022glar, Domen Lestan

    artment, Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, 1000 Ljubljan

    e i n f o

    tober 2011vised form 28 January 2012ruary 2012e 16 February 2012

    soil

    ediation

    a b s t r a c t

    Ten batches (75 kg each) of garden soilZn, 10 mg kg1 Cd and 120 mg kg1 As wwith 60 mmol ethylenediaminetetraa80% of Pb, Zn, Cd and As, respectiveand oral-availability of residual toxicleaching procedure (TCLP), diethylenbased extraction test (PBET) tests. Theelectrochemical advanced oxidation and toxic metals were electro-precipitechnique is separation of the soil frcontaminants) carried out in the samsolution from the previous batch for clsolution in subsequent batches. The coamounted to approximately 75D tonn soil using EDTA

    enia

    >50% of silt and clay and average 1935 mg kg1 Pb, 800 mg kg1

    remediated in a pilot-scale chemical extraction plant. Washingacid (EDTA) per kg of soil on average removed 79, 38, 70, andd signicantly reduced the leachability, phyto-accessibilityls, as assessed using deionised water, toxicity characteristicine pentaacetic acid extraction (DTPA) and physiologically

    soil washing solution was treated before discharge using anss with graphite anode: EDTA was removed by degradation

    onto a stainless steel cathode. The novelty of the remediationhe washing solution and soil rinsing (removal of mobilizedocess step. Another novelty is the reuse of the soil rinsingng the soil sand, soil rinsing and for preparation of the washing

    energy and material expenses and disposal of waste productsoil.

    2012 Elsevier B.V. All rights reserved.

  • D. Voglar, D. Lestan / Journal of Hazardous Materials 215 216 (2012) 32 39 33

    Large volumes of waste solutions are generated, which must betreated before disposal. In addition to highly contaminated wastesoil washing solution obtained after PTM extraction, additionalvolumes of waste rinsing solution, with lower EDTA and PTMconcentrapletely tothe soil af

    The practin a simpl

    Dermonapplicationtwo reporttion Technoagents as aBoth techndownstreamsediments. the scientiPTMs from

    In this pPb, Zn, Cd adegraded ooxidation ponto a staiwaste soil wnology is thsolution ansingle procecosts were of PTMs remmeasured.

    2. Experim

    2.1. Soil sam

    Soil wasetable gardbeen expossmelting. Soare polluteexcavated sthe pilot-scUniversity o

    For stansured in a 1suspensioned Walklethe ammonmethod [11

    2.2. Electro

    The elecand eight smono-polarthe anode:csolution gra6 L min1) fwas pumpedensity on tsupply (Envranged froming the ele

    washing solution in the electolytic cell increased from an initial15 C up to 69 C. During the process, the pH of the washing solu-tion was left unregulated. To keep the voltage near 8 V and reducethe power consumption, we applied up to 730 mL of NaCl (satu-

    olutiue.

    contlyinge andquallutionand tpernchem

    Pb dscharhe en

    witto dited Preatm-cor

    TA d

    conally ethoe3+

    comlate -benophosing

    agnthrod wa

    eioni

    soilesh

    soil3]. Etrat

    abso

    xicit

    tox as d

    il same sizecid af 4.9h a 0red ileach

    M ph

    accine pn w1 M (

    0.05.tion, are also generated (rinsing soil is necessary com- remove EDTA mobilized PTM species which remain inter extraction).ical means of combining soil extraction and soil rinsinge process scheme is another unsolved problem.

    t et al. [3] recently reviewed eld and pilot-scales of physical/chemical soil washing technologies. Onlyed technologies, BioGenesis Sediment Decontamina-logy [7], and NFLs CACITOX process [8], use chelatinguxiliary active compounds in their washing solutions.ologies are a combination of physical separation and

    chemical processes for the treatment of contaminatedTo the best of our knowledge, there are no reports inc literature on full or pilot-scale chemical extraction ofnes-rich contaminated soils using EDTA.ilot-scale experiment, we used EDTA for extraction ofnd As from contaminated garden soil. The EDTA wasn a graphite anode using an electrochemical advancedrocess (EAOP) and the PTMs were electro-precipitatednless-steel cathode before discharge of the cleansedashing solution. The main novelty of the tested tech-e separation of the soil solid phase from the washingd subsequent soil rinsing in a chamber lter press in ass. The remediation efciency and materials and energyevaluated. The mobility, phyto- and oral availabilityaining in the soil after chemical extraction were also

    ental

    ples and analysis

    collected from the 0 to 30 cm surface layer of a veg-en in the Meza Valley, Slovenia. The Meza Valley hased to more than 300 years of active lead mining andils in the valley, including 6600 ha of agricultural land,

    d, primarily with Pb but also with Zn, Cd and As. Theoil was transported to a temporary storage location atale soil remediation plant at the Biotechnical Faculty,f Ljubljana campus.

    dard pedological analysis, the pH in the soil was mea-/2.5 (w/v) ratio of soil and 0.01 M CaCl2 water solution. Soil samples were analyzed for organic matter by modi-yBlack titrations [9], cation exchange capacity (CEC) byium acetate method [10] and soil texture by the pipette].

    lytic cell

    trolytic tank cell (V = 10 L) contained six graphite anodestainless steel cathodes (distance = 10 mm) arranged in

    mode. The overall anode surface area was 2523 cm2;athode surface area ratio was 1:1. Used soil washingvitationally owed into the electrolytic cell (ow raterom the mixing reactor (total working V = 200 L) andd back into the reactor in a closed loop. The currenthe electrodes was kept at 91 mA cm2 using a DC powerit d.o.o., Slovenia). The voltage between the electrodes

    8.1 to 11.6 V, with an average voltage of 8.4 V. Dur-ctrochemical process, the temperature of the treated

    rated sset val

    Themultipvolumtime eing sol3 min the suelectrotion ofwas di

    At tetchedwater deposiafter telectro

    2.3. ED

    ThemetricThe mwith F(trans-by cheand Nchromacid. U535 nmphenadistille

    2.4. D

    The2 mm mto eachture [1Concenatomic

    2.5. To

    TheappliedThe soparticlacetic aa pH othrougand stoin the

    2.6. PT

    PTMetriamsolutioand 0.7.30 on) as electrolyte when the voltage increased over the

    act time of electrochemical treatment was calculated by the operation time with the ratio of the electrode cell

    the volume of washing solution (30 min of operationed 3.56 min of contact time). Samples (20 mL) of wash-

    were collected periodically, centrifuged at 2113 g forhe Pb, Zn and As concentrations measured. The rest ofantant was stored in the cold for further analysis. Theical treatment was terminated when the concentra-

    ecreased below 5 mg L1 and the treated waste solutionged.d of the electrochemical treatment, the cathodes were

    h 220 mL of 65% HNO3 and rinsed with 1780 mL ofssolve and later measure the concentration of electro-TMs. The graphite anodes were weighed before andent of 10 soil batches to determine the amount of

    roded material.

    etermination

    centration of EDTA was determined spectrophoto-according to the procedure of Hamano et al. [12].d involves the reaction of EDTA in washing solutionunder acidic conditions to produce Fe-EDTA chelateplexation), followed by the removal of excess of Fe3+

    extraction in the aqueous phase, using chloroformzoyl-N-phenylhydroxylamine and the formation of are with 4,7-diphenyl-1,10-phenanthroline-disulfonic

    a spectrophotometer, absorbance was measured atainst a blank solution with the 4,7-diphenyl-1,10-line-disulfonic acid replaced with an equal volume ofter. The limit of EDTA quantication was 20 mg L1.

    sed water extraction test

    samples were air-dried, ground and sieved through a again. One hundred mL of deionised water was applied

    sample (10 g) and agitated for 24 h at room tempera-lutriates were ltered through a Whatman no. 4 lter.ions of Pb, Zn, Cd and As were determined using amerption spectrometry (FAAS).

    y characteristic leaching procedure

    icity characteristic leaching procedure (TCLP) wasened by the US Environmental Protection Agency [14].ple specimens were crushed and ground to reduce the

    to less than 2.0 mm and agitated in 20 mL of 0.0992 Mnd 0.0643 M NaOH extraction solution (1:20 ratio) with3 0.05 for 18 h at 300 rpm. The leachate was ltered.45-m membrane lter to remove suspended solidsn the cold for determination of Pb, Zn, Cd and As presentate, using FAAS.

    yto- and oral-accessibility

    essibility for plants was assessed with the diethylen-entaacetic acid (DTPA) test [15]. The DTPA extractionas prepared by mixing 0.005 M DTPA, 0.01 M CaCl2,triethanolamine) TEA and the solution adjusted to pH

    Soil samples (5 g) were sieved through a 2 mm mesh,

  • 34 D. Voglar, D. Lestan / Journal of Hazardous Materials 215 216 (2012) 32 39

    10 mL of DTPA solution was poured over and the mixture shakenfor 2 h on a horizontal shaker at about 120 cycles min1. The sam-ples were ltered through Whatman no. 4 lter paper and analyzedfor Pb, Zn, Cd and As content.

    The phyaccessibilityintestinal d250 m metemperaturtion uid w0.50 g of citacetic acid wmeasured aof 12 M HClat 1500 g volume samconstant votitrated to psmall intest50 mg of pation at conscollected, celyzed for Pbmoistened athe reaction

    2.7. PTMs d

    Air-drieddigested into 100 mL, awith a deumetals in threference m2004.3/4, Wwas used inThe limits oPb, Zn and Cwere also uin the analy

    During tcentration iusing portaDS-4000, OXRF to ASS AsXRF 0.5,cients (R2

    and 0.997 fAAS and XRPTMs. XRF w(10 mg L1)samples.

    3. Pilot-sca

    Ten batcextraction pbut excavatent depths. the soils: pH100 g1 of Since the soloam. The sccess is showwater is als

    3.1. Soil extraction and sand separation

    The excavated garden soil contained almost no gravel or objectslarger than 3 cm. Seventy-ve kg batches of soil (air-dry weight,

    0.2ty 35tch, wassoil bn rintreamsitioaximsionion, wet sof initial b

    Sandutionwaten 3.2paraed s

    illiq

    140rane loven

    50KI-3

    ia). I fromer pren resoil reasuing 1reforbatch

    follo pro: 113n ansed . Theght at (av

    whoused

    prepof so

    furt

    ectro

    ordindischyl ranic pous

    2)M

    /2)esiologically based extraction test (PBET) for oral- assessment involves simulations of human gastric andigestion [16]. The 0.5 g sample was sieved through ash and digested in a reaction ask for 2 h at constante (37 C) in simulated gastric uid (50 mL). The extrac-as prepared by mixing 1.25 g of pepsin (porcine, Sigma),rate, 0.50 g of malate, 420 L of lactic acid and 500 L ofith pH 2.50 0.05. The pH of the reaction mixture was

    nd adjusted if necessary every 5 min with the addition. After 2 h, 5 mL samples were collected and centrifugedfor 25 min; the supernatant was stored at 5 C. The 5 mLples were replaced with gastric solution to maintain alume in the reaction ask. The solution was furtheredH 7 by the addition of NaHCO3 solution; to simulateine conditions, 175 mg of bile salts (porcine, Sigma) andncreatin (porcine, Sigma) were added. After 2 h diges-tant temperature (37 C), the reaction solutions werentrifuged at 1500 g for 25 min, stored at 5 C and ana-, Zn, Cd and As content. During both phases, a constantrgon ow of 1 L min1 at 37 C was conducted through

    mixture in order to simulate peristaltic movement.

    etermination

    soil samples (1 g) were ground in an agate mill, aqua regia (28 mL), diluted with deionized water upnd Pb, Zn and Cd analyzed by ame (acetylene/air) AASterium background correction (Varian, AA240FS). Thee solution were determined by FASS directly. A standardaterial used in inter-laboratory comparisons (Wepalageningen University, Wageningen, The Netherlands)

    the digestion and an...

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