Pilot-scale washing of metal contaminated garden soil using EDTA
Post on 05-Sep-2016
Embed Size (px)
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
cetic ly, an
usedprocetatedom te pr
1 of s
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
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 . 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 .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 , 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: email@example.com (D. Lestan).
chemical extraction, in which the contaminants are selectivelydissolved;
a combination of both physical and chemical processes .
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 . 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. 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 .
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
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
>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.
2.1. Soil sam
Soil wasetable gardbeen expossmelting. Soare polluteexcavated sthe pilot-scUniversity o
For stansured in a 1suspensioned Walklethe ammonmethod [11
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-
contlyinge andquallutionand tpernchem
Pb dscharhe en
witto dited Preatm-cor
tox as d
il same sizecid af 4.9h a 0red ileach
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.  recently reviewed eld and pilot-scales of physical/chemical soil washing technologies. Onlyed technologies, BioGenesis Sediment Decontamina-logy , and NFLs CACITOX process , 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
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 , cation exchange capacity (CEC) byium acetate method  and soil texture by the pipette].
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
ThemetricThe mwith F(trans-by cheand Nchromacid. U535 nmphenadisti