Acid Extraction

Toxic Metal Removal from Polluted Soil by Acid Extraction

Sara Bisone & Jean-François Blais &

Patrick Drogui & Guy Mercier

Received: 6 October 2011 /Accepted: 13 March 2012 /Published online: 29 March 2012# Springer Science+Business Media B.V. 2012

Abstract Sulfuric acid leaching is a promising tech-nique to extract toxic metals from polluted soils. Theobjective of this study was to define the optimum sulfuricacid leaching conditions for decontamination of the fineparticle fraction (<125 μm) of an industrial soil pollutedby Cd (16.8 mg kg−1), Cu (3,350 mg kg−1), Pb(631 mg kg−1) and Zn (3,010 mg kg−1). Batch leachingtests in Erlenmeyer shake flasks showed that a soil pulppH between 1.5 and 2.0 using a solid concentration (SC)ranging from 5 to 20 % is adequate to efficiently solubi-lize toxic metals. Leaching tests performed at differenttemperatures (20, 40, 60 and 80 °C) also revealed that itis not beneficial to heat the soil suspension during theleaching treatment. The application in a 1-L stirred tankreactor of five consecutive 1-h leaching steps at 10 % SCand ambient temperature, followed by three water wash-ings steps resulted in the following metal extractionyields: 30 % As, 90 % Cd, 43 % Co, 7 % Cr, 88 % Cu,75 % Mn, 26 % Ni, 18 % Pb and 86 % Zn. Thedecontaminated soil conformed to Quebec norms forcommercial and industrial use of soil.

Keywords Acid extraction . Contaminated soil .

Metal . PAH . Sequential extraction . Soil-washing

1 Introduction

Soils contaminated with toxic metals and metalloids are amajor environmental concern in industrialized countries.Several thousand sites are polluted by toxic metals inEurope (ETCS 1998; Paspaliaris et al. 2010), NorthAmerica (USEPA 1997a) and China (Li 2006).

The risks associated with the presence of potentiallytoxic metals in soils and water have been intensivelydescribed in literature (Allen 2002; Kabata-Pendias andPendias 2001; Lippmann 2000). Many metallic and met-alloids ions are toxic to living organisms, in particular,humans (Chapman et al. 2003; Florea and Büsselberg2006; Naja and Volesky 2009; Sharma and Agrawal2005). Themetals andmetalloids most often encounteredare lead (Pb), chromium (Cr), mercury (Hg), copper(Cu), zinc (Zn), arsenic (As), nickel (Ni) and cadmium(Cd) (Shammas 2009; USEPA 1997b).

Physical separation technologies, such as gravimetricand magnetic separators, can efficiently remove andconcentrate metals from soils, particularly for large soilparticle fractions (Dermont et al. 2008; Mercier et al.2002). Chemical extraction technologies are frequentlyproposed for removing toxic metals from the finest soilparticle fractions (Dermont et al. 2008; Mercier et al.2007).

Metal solubilization techniques include leachingwith inorganic acids (H3PO4, H2SO4, HCl and HNO3)(Masscheleyn et al. 1999; Neale et al. 1997), organicacids (citric acid, acetic acid, tartaric and acid) (Bassi etal. 2000; Peters 1999;Wuana et al. 2010), autotrophic or

Water Air Soil Pollut (2012) 223:3739–3755DOI 10.1007/s11270-012-1145-1

S. Bisone : J.-F. Blais (*) : P. Drogui :G. MercierInstitut National de la Recherche Scientifique(Centre Eau, Terre et Environnement),Université du Québec,490 rue de la Couronne,Québec, QC, Canada G1K 9A9e-mail: [email protected]

heterotrophic bioleaching (Chen and Lin 2010; Ren etal. 2009), chelating agents (EDTA, EDDS, ADA,DTPA, MGDA, NTA and PDA) (Arwidsson et al.2010; Lestan et al. 2008; Pociecha and Lestan 2010;Zeng et al. 2005) or biosurfactants (Hong et al. 2002;Juwarkar et al. 2007; Mulligan and Wang 2006) andoxidative agents (KMnO4 and H2O2) (Reddy andChinthamreddy 2000).

The possibility of removing metals, primarily Pb,from soils using a concentrated saline (NaCl) solutionas a leaching agent has also been proposed by Nedwedand Clifford (2000) and Djedidi et al. (2005). In thisprocess, chloride ions react with Pb and form solublemetallic species, such as PbCl4

2−, PbCl3− or PbCl2(aq).

Subsequently, metals solubilized by chemical leach-ing can be safely recovered to avoid environmentalcontamination. Heavy metal in soil acid leachates canbe effectively removed by methods of precipitation orco-precipitation (Djedidi et al. 2009; Meunier et al.2006), ion-exchange (Janin et al. 2009), membrane sep-aration (Ortega et al. 2007, 2008), adsorption and bio-sorption (Ahluwalia and Goyal 2007; Demirbas 2008;Meunier et al. 2004), electrocoagulation (Meunier et al.2006, 2009) and electrodeposition (Ortega et al. 2008).

The main objective of the present study on acid ex-traction was to define the optimum acid leaching operat-ing conditions for economic treatment of multi-metallicpolluted industrial soil. The leaching parameters thatwere studied are the following: (1) sulfuric acid concen-tration, (2) soil suspension (solids content) concentration,(3) temperature, (4) leaching duration and (5) number ofleaching steps. This study focused on the treatment of thefine particle soil fraction of the soil (<125 μm). Thecoarse particle fraction of soil (>125 μm) is generallytreated more economically by physical treatment meth-ods (Dermont et al. 2008; Mercier et al. 2002).

2 Methodology

2.1 Soil Sampling and Characterization

Two soil samples (TE-19 and TE-23) were sam-pled from an industrial site located in Montreal(QC, Canada). The soils were sampled with a stainlesssteel shovel from the upper part of the soil (less than30 cm from the surface for the TE-23 sample and atdepths between 0.3 and 1 m for the TE-19 sample) andplaced in 20-L plastic containers.

The granulometry was analyzed using eightsieves sizes as follows: 5, 2, 1, 0.5, 0.25, 0.125,0.0053 and 0.020 mm as described in Mercier et al.(2001). Three samples of each particle size fractionwere digested and analyzed to determine the metalcontent.

2.2 Sequential Extraction and Microanalysis

The fractional speciation of the metals in the soil wasperformed using a modified method from Tessier et al.(1979). Specifically, six fractions of metals wereextracted: exchangeable, bound to carbonates, boundto manganese oxides, bound to ferric oxides, bound toorganic matter and sulfides and linked to the crystallinephase (residual phase).

The soil particle analysis was performed on thinsections of the soil fraction (<0.125 mm) coated withgold. A scanning electron microscope (SEM, CarlZeiss, model EVO®R50) equipped with an X-ray en-ergy dispersion spectrometer (EDS, Oxford Instru-ment, INCAx-sight EDS Detectors) was used. Anaccelerating voltage of 20 kV and a beam current of100 μAwere used, and back scattered incident electronsoil particle images and qualitative chemical analysiswere produced.

2.3 Acid Consumption

Acid consumption during the acidification of the TE-19 and TE-23 soil samples (fraction <125 μm) wasmeasured in agitated 500-mL Erlenmeyer flasks usinga 10 % w/v soil suspension (20 g of soil sample in200 mL water volume). Small amounts (0.1 to 1.0 mL)of a sulfuric acid solution (4 N, ACS grade) wereadded to the soil solutions, and the pH was measuredafter 5 min of agitation.

2.4 Acid Extraction

Almost all of the acid extraction tests were per-formed in triplicate on soil fractions smaller than125 μm. The soil sample (TE-19/23) used for theleaching experiments was an equal weight mixtureof the TE-19 and TE-23 samples. Acid extractionmethods essentially consist of exposing the soils tosolutions for a given time period to solubilize themetals and remove the metals from the contaminat-ed soils. All tests were performed in 500-mL

3740 Water Air Soil Pollut (2012) 223:3739–3755

Erlenmeyer flasks with internal baffles. Followingthe leaching tests, 20 mL samples of the leachateswere filtered using Whatman 934-AH membranes(1.5-μm pore size) and acidified using 5 % HNO3.The acidified samples were analyzed for metal con-centrations using inductively coupled plasma–atomicemission spectroscopy (ICP-OES).

2.4.1 Effect of pH and Temperature

The leaching tests were performed at different pHs(non-adjusted, 3.0, 2.5, 2.0 and 1.5) and temperatureconditions (20, 40, 60 and 80 °C). These tests weredone using a 10 % SC of the TE-19/23 soil sample andfor a 24-h leaching period. The pH of the soil suspen-sion was frequently adjusted during the entire leachingperiod.

2.4.2 Effect of Ferric Chloride and the SodiumChloride Solution

The leaching tests were done at a pH01.5 and at differ-ent temperature conditions (20, 40, 60 and 80 °C) withthe addition of 3 g Fe3+/L (FeCl3, Laboratoire Mat,Québec, Canada) and 2 M NaCl (ACS grade).

2.4.3 Effect of the Solid Concentration and MetalLeaching Kinetic

The leaching tests were done with different solidconcentrations (5, 10, 15 and 20 % SC) of the TE-19/23 soil sample. These tests were performed atambient temperature (20 °C) and at a pH01.5.Five milliliter samples were used in the metalanalysis at different time intervals for a 24-h leachingperiod.

2.4.4 Effect of Successive Leaching and Washing Steps

Five consecutive leaching steps followed by three suc-cessive washing steps were used on the TE-19/23 soilsample. This experiment was done in triplicate using100 g of soil, a 10 % SC solution and at 20 °C. Duringthe leaching steps, the pH was adjusted to 1.5 by addingsulfuric acid. The leaching time was 1 h for each step,and a 5-min period was used for each washing step.Between each leaching and washing step, the soil sus-pensions were separated by centrifugation (3,000×g for15 min).

2.5 Analytical

The pH and redox potential were determined before andafter each experiment using a pH-meter (Accumet Re-search AR25 Dual Channel pH/Ion meter, Fischer Sci-entific Ltd., Nepean, Canada) equipped with a doublejunction Cole-Parmer electrode with an Ag/AgCl refer-ence cell for the pH (daily calibration between 2 and 10).The redox potential was measured with a platinumelectrode. Total solids were measured according to theAPHA method 2540B (APHA 1999).

The total carbon (C), total nitrogen (N) and sulfur (S)were analyzed by a CHNS Leco analyzer. The metals inthe solution were measured by plasma emission spec-troscopy with a simultaneous ICP-OES (Vista Ax CCOsimultaneous ICP-OES from Varian, Mississauga,Canada). Analytical quality controls were performedwith a certified standard solution (PlasmaCal Multiele-ment Standard 900-Q30-100, SCP Science, Baie d’Urfé,Canada).

Concentrated HCl and HNO3 were used for the diges-tion (in triplicates) of 0.5 g of dry soil samples (Centred’expertise en analyse environnementale du QuébecMA.205—Mét/P 1.0, Éd. 2003-12-11). A control(PACS-2, Canada National Research Council, Ottawa,Canada) was also digested in parallel.

3 Results and Discussion

3.1 Soil Characteristics

The physical and chemical characteristics of the soilsamples (fraction<2 mm) are given in Table 1, and theconcentrations of the selected elements are shown inTable 2. Both soil fractions are slightly alkaline (pH8.5–8.6) with a high calcium content of 54 and 82 g Cakg−1 in the TE-19 and TE-23 soils samples, respectively.The organic content in the soil was relatively low, with atotal carbon concentration less than 1 % (<10 gC kg−1).

The analysis of the soil samples under fraction sizesof 2 mm and 125 μm showed that the Cu and Znconcentrations largely exceed criteria C (500 mg Cukg−1 and 1,500 mg Zn kg−1) of the Quebec Governmentfor commercial or industrial use of soil, whereas Cd andPb concentrations were found above criteria B for resi-dential use (5 mg Cd kg−1 and 500 mg Pb kg−1). Theconcentration was under the B and C criteria with anaverage value of 14 mg As kg−1 in the <2-mm soil

Water Air Soil Pollut (2012) 223:3739–3755 3741

fraction. Finally, the Al concentrations were 9,960 and10,300 mg Al kg−1 and the Fe concentrations were

37,800 and 47,700 mg Fe kg−1 for the TE-19 and TE-23, respectively.

3.2 Particle Size and Metal Distributions

The particle size distribution and metal concentrationsin each particle size fraction of the soil samples aregiven in Figs. 1 and 2, respectively.

According to Fig. 1, the coarser fraction of thesoil particles (>2 mm) represents an average of51 % of the soil weight. The weight of the sandfraction (between 53 μm and 2 mm) was equivalentto approximately 43 % of the total soil weight,whereas the silt/clay fraction (<53 μm) constitutedless than 6 % of the soil weight. A pedologist ismore interested in soil whose particles are smallerthan 2 mm because these particles are more activepart in all of the processes. However, in a soil,there is often a lot of coarse sand (2 to 4 mm),gravel (>4 mm) and rocks, and as specified by theMinistry of environment of the province of Qué-bec, those parts of the soil must also respect the

Table 1 Physical and chemical characteristics of the soil sam-ples (fraction <2 mm)

Parameters Units Soil samples

TE-19 TE-23

Humidity % w/w 12.7 10.5

Bulk density g cm−3 0.99 1.03

pH – 8.63 8.51

CECa mEq 100 g−1 21.9 24.4

Total carbon (C) g kg−1 3.9 9.3

Total nitrogen (N) g kg−1 0.16 0.17

Sulfur (S) g kg−1 <0.05 0.10

Phosphorous (P) g kg−1 0.78±0.01 0.65±0.01

Calcium (Ca) g kg−1 54.3±0.4 82.0±8

Magnesium (Mg) g kg−1 5.35±0.06 6.62±0.09

Sodium (Na) g kg−1 0.58±0.01 1.10±0.48

Potassium (K) g kg−1 2.02±0.05 2.42±0.02

a Cation-exchange capacity (milliequivalents per 100 g)

Table 2 Inorganic pollutant concentrations (milligrams per kilogram of dry soil) in the fractions <2 and <0.125 mm of the soil samples

Pollutants Soil fraction<2 mm Soil fraction<0.125 mm Criteriaa

TE-19 TE-23 TE-19 TE-23 TE-19/23 B C

Al 9,960±150 10,300±1,100 13,000±100 11,600±300 12,100±300 – –

As 14.6±0.8 13.3±0.2 14.9±0.9 23.3±1.3 20.1±0.6 30 50

B 46.6±0.9 59.0±8.8 57.4±0.6 58.7±1.4 55.5±1.5 – –

Ba 149±3 152±13 190±2 172±3 177±5 500 2,000

Cd 11.4±0.1 19.0±1.6 12.8±0.1 21.4±0.4 16.8±0.2 5 20

Co 13.2±0.1 11.3±0.6 16.3±0.3 14.3±0.4 14.8±0.5 50 300

Cr 155±3 98.4±3.5 57.7±0.5 46.7±0.6 51.2±1.7 250 800

Cu 3,310±40 3,690±440 3,080±30 3,710±70 3,350±90 100 500

Fe 37,800±600 47,700±7,100 35,900±200 35,900±600 35,300±700 - -

Mn 598±6 410±10 780±5 612±9 688±20 1,000 2,200

Mo 7.23±0.19 7.41±1.22 2.64±0.08 2.79±0.16 2.84±0.22 10 40

Ni 31.0±0.1 33.6±0.2 37.0±0.2 49.3±0.8 42.3±0.6 100 500

Pb 920±155 464±25 584±7 705±8 631±5 500 1,000

Sb 3.37±0.37 0.54±0.11 2.41±0.41 1.24±0.42 1.54±0.79 – –

Si 1,920±25 2,520±610 1,280±50 1,350±30 1,340±60 – –

Sn 10.8±0.4 42.2±20.7 4.95±0.40 5.31±0.30 5.26±0.60 50 300

Ti 313±6 525±114 322±3 405±6 362±7 – –

Zn 2,830±10 3,100±710 3,330±20 2,830±60 3,010±30 500 1,500

a Regulatory level into force in Quebec (Canada), for residential use (criteria B) and commercial/industrial use (criteria C) (Ministère dudéveloppement durable de l’environnement et des parcs du Québec 1999)


contaminant concentration limits established in theregulation.

The analysis of the metal distributions of thedifferent particle size fractions of the soil revealedthat no physical treatment involving only particlesize separation of the soil is possible. In fact,Fig. 2 shows that all of the particle size fractionsexceeded criteria C for Cu and Zn concentrationsand exceeded criteria B for Cd. The observation ofthe metals distribution in the different particle sizefractions does not allow the establishment of a relation-ship between the metal content and the particle size ofthis soil.

3.3 Metal Speciation

The metal proportions of each fraction in the TE-19and TE-23 soil samples resulting from the Tessier’sspeciation procedure are shown in Fig. 3. The metaldistributions in both soil fractions are comparable. Cr(76–78 %), Fe (75–77 %), Mn (30–32 %) and Ni (46–51 %) are primarily found in the residual fraction ofthe soil, whereas Cd (26–33 %), Cu (55–56 %), Pb(46–51 %) and Zn (39–66 %) are mostly associatedwith Fe oxides. Tessier’s procedure also showed that asignificant proportion of Cd (37–40 %), Cu (8–21 %),Mn (20–22 %), Pb (17–25 %) and Zn (10–28 %) islinked to carbonates.

3.4 SEM–EDS Analysis

SEM–EDS analysis of the soil particles (Fig. 4 andTable 3) showed that 59 % of the observed particlescontaining Cu consisted of copper oxides (Cu2O orCuO); examples of both are reported in Fig. 4a, b,respectively. Twenty-eight percent of the Cu-contaminated particles were primarily composed ofiron oxides. In Fig. 4c, an example is shown of aparticle composed of iron oxide that contained copper.According to the EDS-analysis (atomic percentages:55.8 % O; 38.3 % Fe; 4.4 % Cu; 1.5 % Al), the ironoxide should be Fe2O3.

Ten percent of the Cu-containing particles are slagresidues, where copper oxides or copper sulfide areincluded in the volume of a carrying phase primarilycomposed of silicon oxides, iron oxides and smallerconcentrations of Ca, Zn, Al, K and Mg (Fig. 4d).Finally, 3 % of the observed Cu was included inminerals other than iron or copper oxides. Zn is moredifficult to observe. The detected Zn was found as partof the slag-carrying phase, and no free particles of Znwere found.

There is coherence between the SEM observationsand the sequential extraction results. It is possible thatCuO and Cu2O are solubilized with strong acid condi-tions used to extract iron oxides; furthermore, a smallerquantity should have solubilized at the weak acid

Fig. 1 Particle sizedistribution (w/w) ofthe of the soil samplesTE-19 and TE-23


Fig. 2 Metal concentrations in the different particle size fractions of the soil samples TE-19 and TE-23


condition (low pH), which was used to extractcarbonate-bounded metals in Tessier's method. It is ev-ident that the two methods give different information.

Sequential extraction is useful to anticipate the leachingbehavior of soil, whereas SEM analysis gives moreinformation on the contamination characteristics but is

Fig. 3 Metal speciationin the <0.125 mm fractionof the soil samples TE-19and TE-23


not completely reliable for determining the precise metaldistribution because of the difficulties to observe andanalyze very small particles.

3.5 Acid Consumption

The pH decrease during the sulfuric acid additionin the TE-19 and TE-23 soil samples is shown inFig. 5. The acidification curves of the two soilsamples are clearly different because more acidwas required to decrease the pH of the TE-23 soilsuspension (10 % SC). In comparison, 95 and165 kg H2SO4 t−1 of dry soil were required toreach a pH02.0 for the TE-19 and TE-23 soilsamples, respectively. Similarly, 150 and 225 kgH2SO4 t−1 were required to reach a pH01.5 withthe TE-19 and TE-23 soil samples, respectively.

During the acid extraction assays, an equal weightmixture of the TE-19 and TE-23 samples wasused. In this case, an average acid consumptionof 185 kg H2SO4 t−1 was required to reach pH01.5with 10 % SC.

It should be noted that sulfuric acid is the mostinexpensive inorganic acid (approximately 80$/ton ofconcentrated H2SO4). For that reason, it was used formetal solubilization of the TE-19 and TE-23 soilsamples.

3.6 Acid Extraction Assays

3.6.1 Effect of pH

Figure 6 illustrates the metal solubilizations during theleaching tests (24 h, 10 % SC) at different pHs andtemperature conditions. Comparing the metal extractionfor the four temperatures tested, the difference betweenthe pH was highly significant with a P<0.001 for allmetals considered (Friedman test was applied).

The results showed that a decrease of 2.0 in pH orless is required to efficiently solubilize Cu and Zn. AWilcoxon test when the pH01.5 and pH02.0 showeda significant difference for both metals (P<0.001);consequently, a pH of 1.5 was chosen for successiveextractions tests. Cd was also extracted more easily

d

Cu2O

CuO

Fe2O3,CuCuO

Fe,Si,O,Ca,Zn,Al,K

a b

c

Fig. 4 Back-scatteredimage of <0.125 mmfraction of the soil samplesTE-19 and TE-23. a Ironoxide with a small percentageof Cu b Cu2O, c CuO and dCuO included in a slag-carrying phase

Table 3 Mineralogical study on fraction <0.125 mm

Metals Carrying phase (%)

Copper oxide Iron oxide Slag Other minerals

Cu 59 28 10 3

Zn – – 100 –

Repartition of Cu and Zn


(≥80 %) with a pH of 2.5 or less; however, the differ-ence between when the pH was 1.5 or 2.0 was notsignificant (P00.133). In contrast, Pb was weaklysolubilized, even in very acidic conditions (removalof 9 % at pH01.5 and 40 °C), which can be explainedby the low solubility of PbSO4. The addition of NaClcould significantly improve the solubilization of leadfrom soil (Djedidi et al. 2005).

Moreover, As and Cr were marginally extracted at allconditions tested. In fact, the highest solubilizationyields (18 % As and 12 % Cr) were measured after24 h of leaching at a pH01.5 and 20 °C. Cheng et al.(2011) showed that 0.5 M HCl and 0.5 M citric acid arenot efficient in solubilizing chromium from differenttypes of soils. Reddy and Chinthamreddy (2000) alsoshowed that the use of oxidizing agents, such as KMnO4

or H2O2, is required for efficient chromium solubiliza-tion and have also showed that other acids (acetic acid,phosphoric acid) or chelating agents (EDTA and citricacid) were not efficient in extracting chromium.

Tokunaga and Hakuta (2002) and Ko et al. (2006)showed that H3PO4 is slightly more efficient than H2SO4

for arsenic solubilization from contaminated soils. How-ever, these studies demonstrated that the use of H2SO4

allows for a greater extraction of this element than HClor HNO3. In fact, in the cases where arsenic extraction isabsolutely required, the use of H3PO4 or NaOH is rec-ommended (Giacomino et al. 2010; Jang et al. 2005).

3.6.2 Effect of Temperature

The effect of temperature on metal solubilization isshown in Fig. 6. The metal solubilization yields mea-sured after 24 h for tests performed at 20 °C were notsignificantly different from that of the leaching testsperformed at 40 and 60 °C (P00.25 for As, P00.44for Cd, P00.10 for Cr, P00.39 for Cu and P00.272for Zn, using the Friedman test). Moreover, for As,Cd, Cr, Cu and Zn, the leaching tests at 80 °Cexhibited worse performances than those at lowertemperatures for solubilization yields after 1, 2 and4 h. The difference between temperatures becamesignificant, with P values always less than 0.01. Beingable to operate the leaching process at ambient tem-perature is an important advantage because it avoidsheating the soil suspension and can reduce the treat-ment costs.

3.6.3 Effect of Ferric Chloride and Sodium ChlorideSolution

The influence of adding sodium chloride (2 M NaCl)and ferric chloride (3 g Fe3+ L−1) to the soil suspensionduring leaching tests is also shown in Fig. 6. Previousstudies have shown that the addition of a chloride saltenhances the solubilization of Pb from polluted soils byproducing soluble lead chlorocomplexes (Djedidi et al.

Fig. 5 Sulfuric acidconsumption for theacidification of thesoil samples TE-19and TE-23


Fig. 6 Metals solubilization from TE-19/23 soil sample after 24 h in different leaching and temperature conditions (SC010 %)


2005; Nedwed and Clifford 2000). Similarly, ferric saltscan be used as leaching reagents to solubilize Cu ionsfrom solid matrixes (Bouda et al. 2009; Bradley et al.1992).

Figure 6 reveals that the addition of ferric chlorideand sodium chloride is beneficial to solubilize Pb. Com-paring the Pb solubilization at the same pH condition(1.5) and temperature, the difference is highly signifi-cant (P<0.001 with the Wilcoxon test). Then, at 20 °Cand pH01.5, the Pb solubilization yield increased from5 to 64 % with these leaching agents. It is clear that theincrease of lead solubilization is linked to the presenceof a very high chloride concentration (2 M).

However, the addition of ferric ions (3 g Fe3+ L−1)in the leaching solution (this increases the redox po-tential of the solution) did not improve the solubiliza-tion of the other metals. In addition, the comparison ofsolubilization yield during 24 h at the four temper-atures revealed that extraction without ferric ions andNaCl is significantly better for Cu and Zn (P00.002and P00.001, respectively).

Because the initial Pb concentration in the studiedsoil was under criteria C, the addition of sodium chlo-ride was not used in the next step.

3.6.4 Effect of the Solid Concentration

Figure 7 shows the metal solubilizations during theleaching tests (pH01.5 and T020 °C) with differenttotal solid concentrations (SC). Although the differencebetween the SC is statistically significant (P<0.001with a 2 factor ANOVA), the solubilization curvesshow that Cd, Cr, Cu and Zn are not greatly influencedby a SC ranging from 5 to 20 %. In fact, therewas only a slight increase in solubilization for thetest performed using 5 % SC in comparison withthe other tests. However, the variation of the As andPb solubilization was more important in relation tothe SC, where the solubilization yields ranged between3 and 22 % for As and 3 to 10 % for Pb after 24 h ofleaching. Finally, the difference between 15 and 20 %was not significant for Cu and As and barely significantfor Cd.

3.6.5 Metal Leaching Kinetics

Figure 7 shows the kinetics of the metal solubilizationduring the leaching experiments. The principal phenom-enon observed was that metal solubilization is mostly

achieved in the first hours of leaching. For As andPb, the maximum solubilization yields (10 % Asand 8 % Pb at 10 % SC) were reached after only1 h of acid leaching. In the same manner, 74, 47and 66 % of Cd, Cu and Zn, respectively, weremeasured at 10 % SC after 1 h. However, for thesemetals, the removal yields slowly increased to reachmaximum values (86 % Cd, 75 % Cu and 81 % Zn)after 24 h of treatment.

Contact time is an important parameter from an eco-nomic point-of-view for soil decontamination using acidextraction techniques. Instead of using a long reactionperiod, such as 24 h, to reach goodmetal removal yields,it would bemore economic and efficient to apply severalsuccessive short leaching treatments. This approach wasverified in this study.

3.6.6 Effect of Successive Leaching and Washing Steps

The acid consumption associated with each of the fivesuccessive leaching steps followed by washing stepsof the soil is shown in Table 4. The corresponding pHand redox potential values of the soil suspension arealso given. The pH and redox potential conditionsduring the five consecutive leaching treatments wererelatively stable with a pH range of 1.36 to 1.60 and aredox potential range of 483 to 495 mV. The acidconsumption was equivalent to 185 kg t−1 of treatedsoil for the first leaching step, which markedly de-creased from 78 to 47 kg t-1 for the last four leachingsteps. The total acid consumption for the five leachingtreatments was 422 kg H2SO4 t

−1.It is also important to note that an average mass of

84.0±1.2 g (dry basis) of decontaminated soil wasrecovered after the leaching and washing steps. Con-sequently, a weight loss of 16 % of the initial soil mass(100 g) was recorded during the process. The final SCvalue of the decontaminated soil after dewatering bycentrifugation was 57.7±0.2 %.

The soluble Cu, Zn and Mn concentrations in thedifferent leachates and rinsing waters produced duringthe successive leaching and washing steps are pre-sented in Fig. 8. The soluble metal concentrationsmeasured after each leaching and washing steprevealed that the metal solubilization is almost com-plete after three leaching steps. Then the soluble Cu,Mn and Zn concentrations measured after the fourthleaching treatment were under 10 mg L−1. In the samematter, the soluble metal concentrations in the waters


Fig. 7 Kinetic of metals solubilization from TE-19/23 soil sample during sulfuric acid leaching (pH01.5, T020°C) using differentsolids concentrations (SC)


from the third washing step are very low, with valuesless than 0.5 mg L−1.

Figure 9 illustrates the final solubilization yields ofthe different metals obtained during the successiveleaching and washing steps and also shows that themetals solubilization is mostly done in the first threeleaching steps. The cumulative solubilization yieldsobtained after the three leaching steps were the fol-lowing: 36 % As, 99 % Cd, 51 % Co, 17 % Cr, 101 %Cu, 86 % Mn, 35 % Ni, 18 % Pb and 96 % Zn. Bycomparison, the total solubilization yields determinedafter five leaching steps and three washing steps were47 % As, 103 % Cd, 54 % Co, 21 % Cr, 107 % Cu,89 % Mn, 40 % Ni, 32 % Pb and 101 % Zn. Conse-quently, it appears that three leaching steps with one or

two washing steps would be sufficient for treating thissoil.

Table 5 presents the mass balance (in terms ofmilligrams of metal) of the different metals analyzedduring the successive leaching and washing steps. Themass balance results for this experiment are very good,with the O/I ratio ranging from 0.95 to 1.10. The finalmetal extraction yields based on residual metal con-tents in the decontaminated soil in comparison withthe initial metal contents in the soil were the follow-ing: 30.0 % As, 90.0 % Cd, 43.1 % Co, 7.4 % Cr,87.7 % Cu, 74.7 % Mn, 26.4 % Ni, 17.7 % Pb and85.6 % Zn.

The performance of this acid leaching process wasalso evaluated on the basis of the final metal concen-trations in the decontaminated soil. The residual con-centrations in the treated soil were the following: 16.7±3.0 mg As kg−1, 1.7±0.2 mg Cd kg−1, 11.5±0.8 mgCo kg−1, 85.4±7.6 mg Cr kg−1, 394±51 mg Cu kg−1,222±16 mg Mn kg−1, 38.7±3.0 mg Ni kg−1, 535±55 mg Pb kg−1 and 523±55 mg Zn kg−1. These concen-trations are under criteria C (Table 2) for all the testedmetals, and only Cu, Pb and Zn exceed criteria B forresidential use of the soil.

The use of three leaching steps with a 10 % soilsuspension would require a large volume of water fortreating contaminated soil. Using a counter-current leach-ing process (CCLP) with water recycling after metalprecipitation would allow a significant reduction of the

Table 4 Operating parameters for the decontamination of theTE-19/23 soil sample using multiple leaching and washing steps(leaching time01 h, T020 °C, PD010 %)

Leachingsteps

pH ORP (mV) Acid consumption(kg H2SO4 t

−1)

Lix 1 1.60±0.16 490±8 185±15

Lix 2 1.44±0.05 494±6 78±28

Lix 3 1.49±0.07 485±10 62±16

Lix 4 1.36±0.04 488±3 50±7

Lix 5 1.41±0.02 483±3 47±10

Total – – 422±44

Fig. 8 Solubilized metalsconcentrations after thedifferent leaching andwashing steps fromTE-19/23 soil sample(pH01.5, leachingtime01 h, T020°C,SC010 %)


required process water. For example, Janin et al. (2012)reduced by 12 times the required process water volumefor decontamination (copper leaching with sulfuric acid)of copper azole treated wood waste using the CCLPapproach. These authors also showed that this techniquereduced the acid consumption by 86 % in comparisonwith the conventional acid leaching procedure. The in-terest in CCLP for soil decontamination by acid

washings was also demonstrated by Masscheleynet al. (1999).

Using a counter-current leaching procedure, theacid consumption should be approximately equivalentto the acid requirement for the first leaching step(~185 kg t−1). In this case, the cost for the H2SO4 isestimated at 16$ t−1 (80$ t−1 H2SO4 at 93 % w/w). It ispossible to compare this cost with the use of other

Fig. 9 Metals solubilizationyields after the differentleaching and washingsteps from TE-19/23soil sample (pH01.5,leaching time01 h,T020°C, SC010 %)

Table 5 Mass balance (milligrams) of the metals for the decontamination of the TE-19/23 soil sample using multiple leaching and washingsteps (leaching time01 h, T020 °C, PD010 %)

Cu Zn Mn As Cd Co Cr Ni Pb

Input

Initial soil 268.900 305.233 73.487 1.997 1.412 1.691 7.755 4.416 54.583

Total—input 268.900 305.233 73.487 1.997 1.412 1.691 7.755 4.416 54.583

Output

Lix 1 155.763 185.636 39.646 0.165 0.894 0.526 0.557 0.771 2.947

Lix 2 49.606 42.895 9.568 0.270 0.193 0.134 0.324 0.317 3.134

Lix 3 18.179 12.744 2.634 0.167 0.055 0.045 0.197 0.169 2.140

Lix 4 8.001 5.499 0.982 0.104 0.024 0.022 0.129 0.099 2.337

Lix 5 4.519 3.441 0.513 0.075 0.015 0.015 0.088 0.070 2.158

Rin 1 1.262 1.508 0.190 0.005 0.007 0.006 0.036 0.033 1.165

Rin 2 0.263 0.746 0.060 0.001 0.003 0.003 0.013 0.013 0.674

Rin 3 0.122 0.497 0.029 0.000 0.003 0.001 0.006 0.007 0.573

Decontaminated soil 33.128 43.980 18.615 1.400 0.142 0.963 7.180 3.249 44.930

Total—Output 270.842 296.945 72.238 2.187 1.336 1.713 8.531 4.729 60.058

Ratio O/I 1.007 0.973 0.983 1.095 0.946 1.013 1.100 1.071 1.100


inorganic acids. For the same quantity of protons(H+) required to extract the metals, the HCl, HNO3 andH3PO4 requirements would be 138, 238 and 123 kg t−1,respectively. The industrial price for these three acidsare approximately 85$ t−1 (HCl 35 %), 220$ t−1 (HNO3

67 %) and 450$ t−1 (H3PO4 75 %), respectively. Con-sequently, the cost for acid consumption is estimated at34$ t−1 (HCl), 78 $ t−1 (HNO3) and 74$ t−1 (H3PO4).Clearly, in these conditions, using sulfuric acid is themost interesting option from an economic point-of-viewfor metals extraction from polluted soils. Moreover,using H2SO4 as a leaching agent allows the same metalsolubilization as using other inorganic acids (H3PO4,HCl and HNO3; Ko et al. 2006; Moutsatsou et al.2006; Tokunaga and Hakuta 2002), with the exceptionof lead; thus, it appears that the use of this acid is a goodchoice for soil decontamination.

The extraction efficiency is primarily related to theeffective pH achieved and/or the presence of complex-ing anions, such as chlorocomplex, which greatlyincreases the soluble concentration of lead at a partic-ular pH. If the soil is a calcareous soil, complexinganions will increase the quantity of acid to establish aparticular acidic pH, which is an important cost pa-rameter. Moreover, calcareous soil would probablydissolve itself and liberate carbon dioxide at a pH01.5 (the pH used here), and thus, it would be quiteproblematic to apply this process on calcareous soil. Asoil with a high organic matter content would probablybe less problematic to treat than calcareous soil be-cause the organic matter will not be destroyed as muchat this pH due to the relatively short residence time.The organic matter would consume more acid than thesilicate portion of the soil but would consume muchless acid than the calcareous soil.

4 Conclusion

The optimum sulfuric acid leaching conditions weredetermined for the decontamination of the fine particlefraction (<125 μm) of an industrial soil heavily pollutedwith Cu and Zn andmoderately contaminated byCd andPb. This study showed that a pH range of 1.5 to 2.0 witha SC ranging from 5 to 20 % is adequate to efficientlysolubilize toxic metals, and it was not necessary to heatthe soil suspension during the leaching treatment. Theapplication of three to five short (1 h), consecutiveleaching steps followed by one to three washing steps

was sufficient to extract a large part of the toxic metalsinitially present in the polluted soil. The following metalextraction yields were reached after five consecutive1-h leaching steps at 10 % SC and at ambient tempera-ture followed by three water washing steps: 30 % As,90 % Cd, 43 % Co, 7 % Cr, 88 % Cu, 75 % Mn, 26 %Ni, 18 % Pb and 86 % Zn.

Acknowledgments This project was funded by NSERC CRDand Tecosol Inc. The authors would like to express their grati-tude to Lan Huong Tran and Myriam Chartier for their technicalassistance.

References

Ahluwalia, S. S., & Goyal, D. (2007). Microbial and plant derivedbiomass for removal of heavy metals from wastewater. Bio-resource Technology, 98(12), 2243–2257.

Allen, H. E. (2002). Bioavailability of metals in terrestrialecosystems: importance of partitioning for bioavailabilityto invertebrates, microbes, and plants (p. 176). Pensacola:Society of Environmental Toxicology and Chemistry(SETAC.

APHA. (1999). Standards methods for examination of waterand wastewaters. Washington, DC: American PublicHealth Association (APHA), American Water Works As-sociation (AWWA) and Water Pollution Control Federation(WPCF).

Arwidsson, Z., Elgh-Dalgren, K., von Kronhelm, T., Sjoberg,R., Allard, B., & van Hees, P. (2010). Remediation ofheavy metal contaminated soil washing residues with ami-no polycarboxylic acids. Journal of Hazardous Materials,173(1–3), 697–704.

Bassi, R., Prasher, S. O., & Simpson, B. K. (2000). Extraction ofmetals from a contaminated sandy soil using citric acid.Environmental Progress, 19, 275–282.

Bouda, M., Hammy, F., Mercier, G., & Blais, J. F. (2009). Chemicalleaching of metals from sewage sludge: comparative study byuse three oxidizing agents (H2O2, FeCl3 and Fe2(SO4)3).WaterEnvironment Research, 81(5), 523–531.

Bradley, C. P., Sohn, H. Y., & McCarter, M. K. (1992). Model forferric sulfate leaching of copper ores containing a variety ofsulfideminerals. Part I. Modeling uniform size ore fragments.Metallurgical Transactions, 23B, 537–548.

Chapman, P. M., Wang, F., Janssen, C. R., Goulet, R. R., &Kamunde, C. N. (2003). Conducting ecological risk assess-ments of inorganic metals and metalloids: current status.Human and Ecology Risk Assessment, 9, 641–697.

Chen, S. Y., & Lin, P. L. (2010). Optimization of operatingparameters for the metal bioleaching process of contami-nated soil. Separation and Purification Technology, 71(2),178–185.

Cheng, S. F., Huang, C. Y., & Tu, Y. T. (2011). Remediation ofsoils contaminated with chromium using citric and hydro-chloric acids: the role of chromium fractionation in chro-mium leaching. Environmental Technology, 32(8), 879–889.


Demirbas, A. (2008). Heavy metal adsorption onto agro-basedwaste materials: a review. Journal of Hazardous Materials,157, 220–229.

Dermont, G., Bergeron, M., Mercier, G., & Richer-Laflèche, M.(2008). Soil washing for metal removal: a review of physical/chemical technologies and field applications. Journal ofHazardous Materials, 152, 1–31.

Djedidi, Z., Drogui, P., Ben Cheikh, R., Mercier, G., & Blais, J. F.(2005). Lead removal from soil using a saline leaching treat-ment and an electrolytic recovery process. Journal of Environ-mental Engineering Division ASCE, 131(2), 305–314.

Djedidi, Z., Bouda, M., Souissi, M. A., Ben Cheikh, R., Mercier,G., Tyagi, R. D., & Blais, J. F. (2009). Metals removal fromsoil, fly ash and sewage sludge leachates by precipitation anddewatering properties of the generated sludge. Journal ofHazardous Materials, 172, 1372–1382.

European Topic Centre Soil (ETCS). (1998). Topic report—contaminated sites. Copenhagen: European EnvironmentAgency.

Florea, A. M., & Büsselberg, D. (2006). Occurence, use andpotential toxic effects of metals and metal compounds.BioMetals, 19, 419–427.

Giacomino, A., Malandrino, M., Abollino, O., Velayutham, M.,Chinnathangavel, T., & Mentasti, E. (2010). An approachfor arsenic in a contaminated soil: speciation, fractionation,extraction and effluent decontamination. EnvironmentalPollution, 158, 416–423.

Hong, K. J., Tokunaga, S., & Kajiuchi, T. (2002). Evaluation ofremediation process with plant-derived biosurfactant for re-covery of heavy metals from contaminated soils. Chemo-sphere, 49, 379–387.

Jang, M., Hwang, J. S., Choi, S. I., & Park, J. K. (2005).Remediation of arsenic-contaminated soils and washingeffluents. Chemosphere, 60, 344–354.

Janin, A., Blais, J. F., Mercier, G., & Drogui, P. (2009). Selec-tive recovery of metals in leachate from chromated copperarsenate treated wood using ion exchange resins and chem-ical precipitation. Journal of Hazardous Materials, 169,1099–1105.

Janin, A., Riche, P., Blais, J.F., Mercier, G., Cooper, P. &Morris, P. (2012). Counter-current acid leaching processof copper azole treated wood waste. Environ. Technol. (inpress).

Juwarkar, A. A., Nair, A., Dubey, K. V., Singh, S. K., & Devotta,S. (2007). Biosurfactant technology for remediation of cad-mium and lead contaminated soils. Chemosphere, 68(10),1996–2002.

Kabata-Pendias, A., & Pendias, H. (2001). Trace elements insoils and plants (3rd ed., p. 413). Boca Raton: CRC PressLLC.

Ko, I., Lee, C. H., Lee, K. P., Lee, S. W., & Kim, K. W. (2006).Remediation of soil contaminated with arsenic, zinc, andnickel by pilot-scale soil washing. Environmental Progress,25(1), 39–48.

Lestan, D., Luo, C. L., & Li, X. D. (2008). The use of chelatingagents in the remediation of metal-contaminated soils: areview. Environmental Pollution, 153, 3–13.

Li, M. S. (2006). Ecological restoration of mineland with particu-lar reference to the metalliferous mine wasteland in China: areview of research and practice. Environmental Pollution,347, 38–53.

Lippmann,M. (2000).Environmental toxicants. Human exposuresand their health effects (p. 987). New York: Wiley.

Masscheleyn, P. H., Tack, F. M., & Verloo, M. G. (1999). A modelfor evaluating the feasibility of an extraction procedure forheavymetal removal from contaminated soils.Water, Air, andSoil Pollution, 113, 63–76.

MDDEPQ (1999). Politique de protection des sols et de réha-bilitation des terrains contaminés. Annexe 2 : les critèresgénériques pour les sols et pour les eaux souterraines.Ministère du développement durable de l’environnementet des parcs du Québec, Gouvernement du Québec, Québec,QC, Canada.

Mercier, G., Duchesne, J., & Blackburn, D. (2001). Removal ofmetals from contaminated soils by mineral precessing tech-niques followed by chemical leaching. Water, Air, and SoilPollution, 135, 105–130.

Mercier, G., Duchesne, J., & Blackburn, D. (2002). Removal ofmetals from contaminated soils by mineral processing tech-niques followed by chemical leaching. Water, Air, and SoilPollution, 135, 105–130.

Mercier, G., Blais, J. F., & Chartier, M. (2007). Pilot-scaledecontamination of soils polluted with toxic metals bymineral processing technology and chemical leaching.Journal of Environmental Engineering and Science, 6(1),53–64.

Meunier, N., Blais, J. F., & Tyagi, R. D. (2004). Removal ofheavy metals from acid soil leachate using cocoa shells in acounter-current sorption process. Hydrometallurgy, 73(3/4), 225–235.

Meunier, N., Drogui, P., Montané, C., Hausler, R., Mercier, G.,& Blais, J. F. (2006). Comparison between electrocoagula-tion and chemical precipitation for metals removal fromacidic soil leachate. Journal of Hazardous Materials,B137, 581–590.

Meunier, N., Drogui, P., Mercier, G., & Blais, J. F. (2009). Treat-ment of metal-loaded soil leachates by electrocoagulation.Separation and Purification Technology, 67(1), 110–116.

Moutsatsou, A., Gregou, M., Matsas, D., & Protonotarios, V.(2006). Washing as a remediation technology applicable insoils heavily polluted by mining-metallurgical activities.Chemosphere, 63, 1632–1640.

Mulligan, C. N., & Wang, S. L. (2006). Remediation of a heavymetal-contaminated soil by a rhamnolipid foam. EngineeringGeology, 85(1–2), 75–81.

Naja, G. M., & Volesky, B. (2009). Toxicity and sources of Pb,Cd, Hg, Cr, As, and radionuclides in the environment. In L.K. Wang, J. P. Chen, Y. T. Hung, & N. K. Shammas (Eds.),Heavy metals in the environment. Chap. 2 (pp. 13–61).Boca Raton: CRC Press, Taylor & Francis Group.

Neale, C. N., Bricka, R. M., & Chao, A. C. (1997). Evaluatingacids and chelating agents for removing heavy metals fromcontaminated soils. Environmental Progress, 16, 274–280.

Nedwed, T., &Clifford, D. A. (2000). Feasibility of extracting leadfrom lead battery recycling site soil using high-concentrationchloride solutions. Environmental Progress, 19, 197–206.

Ortega, L. M., Lebrun, R., Blais, J. F., & Hausler, R. (2007).Treatment of a soil acidic leachate containing metal ions bynanofiltration membranes. Separation and PurificationTechnology, 54(3), 306–314.

Ortega, L. M., Lebrun, R., Blais, J. F., Hausler, R., & Drogui, P.(2008). Effectiveness of soil washing, nanofiltration and


electrochemical treatment for the recovery of metal ionscoming from a contaminated soil. Water Research, 42(8–9), 1943–1952.

Paspaliaris, I., Papassiopi, N., Xenidis, A., & Hung, Y. T.(2010). Soil remediation. In L. K. Wang, Y. T. Hung,& N. K. Shammas (Eds.), Handbook of advancedindustrial and hazardous wastes treatment. Chap. 14(pp. 519–570). Boca Raton: CRC Press, Taylor & FrancisGroup.

Peters, R. W. (1999). Chelant extraction of heavy metals fromcontaminated soils. Journal of Hazardous Materials, 66,151–210.

Pociecha, M., & Lestan, D. (2010). Electrochemical EDTArecycling with sacrificial Al anode for remediation of Pbcontaminated soil. Environmental Pollution, 158(8), 2710–2715.

Reddy, K. R., & Chinthamreddy, S. (2000). Comparison ofextractants for removing heavy metals from contaminatedclayey soils. Soil Sediment Contamination, 9, 449–462.

Ren, W. X., Li, P. J., Geng, Y., & Li, X. J. (2009). Biologicalleaching of heavy metals from a contaminated soil byAspergillus niger. Journal of Hazardous Materials, 167(1–3), 164–169.

Shammas, N. K. (2009). Management and removal of heavymetals from contaminated soil. In L. K. Wang, J. P. Chen,Y. T. Hung, & N. K. Shammas (Eds.), Heavy metals in the

environment. Chap. 13 (pp. 381–429). Boca Raton: CRCPress, Taylor & Francis Group.

Sharma, R. K., & Agrawal, M. (2005). Biological effects of heavymetals: an overview. Journal of Environmental Biology, 26(2), 301–313.

Tessier, A., Campbell, P. G. C., & Bisson, M. (1979). Sequentialextraction procedure for the speciation of particulate tracemetals. Analytical Chemistry, 51(7), 844–851.

Tokunaga, S., & Hakuta, T. (2002). Acid washing and stabilizationof an artificial arsenic-contaminated soil. Chemosphere, 46,31–38.

USEPA. (1997a). Clean up the nation’s waste sites: markets andtechnology trends. EPA/542/R-96/005, U.S. EnvironmentalProtection Agency, Washington, D.C.

USEPA. (1997b). Technology alternatives for the remediation ofsoils contaminated with As, Cd, Cr, Hg, and Pb. EPA/540/S-97/500, U.S. Environmental Protection Agency, Washington,D.C.

Wuana, R. A., Okieimen, F. E., & Imborvungu, J. A. (2010).Removal of heavy metals from a contaminated soil usingorganic chelating acids. International journal of Environmen-tal Science and Technology, 7(3), 485–496.

Zeng, Q. R., Sauve, S., Allen, H. E., & Hendershot, W. H.(2005). Recycling EDTA solutions used to remediatemetal-polluted soils. Environmental Pollution, 133(2),225–231.


Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

Acid Extraction

Documents

Transcript of Acid Extraction