Amphoteric Surfactants for PAH and Lead Polluted-Soil

8/11/2019 Amphoteric Surfactants for PAH and Lead Polluted-Soil

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Beyond the CMC, addition of surfactant has no effect on surface tension. CMC varies for each surfactant andis a function of temperature, ionic bonds and the presence of organic and/or mineral additives (Haigh1996 ), nature of the functional groups at the interface,molecular structure, aqueous phase environment (pH,

temperature, additives, electrolyte) (Rosen 1989). In asoil/solution system, the solubilization of organiccompounds occurs at effective surfactant concentra-tions (CMC eff ) higher than CMC in pure water (Zhengand Obbard 2002).

Contaminants are many and varied. Inorganic con-taminants toxicity is dependent of metal speciation,absorption mode, type of impacted organisms, andmetal concentrations. If some metals are known as lifeessential oligo-elements (Zn, Cu), many others are toxicand cumulative (Pb, Cd) (Lippmann 2000 ; Allen 2002).

Various treatment processes exist (biological, physico-chemical, thermal) (USEPA 2004 ). Soilwashing is an ex situ process. This is done bydissolving/transferring or concentrating (Mulligan et al. 2001a ). Biosurfactants for soil and groundwater treatment can be used (Mulligan et al. 2001b ). Metals,the semi-volatile organics, PAHs, pesticides andPCBs can be treated by soil washing (Mann 1999 ).Many studies concern surfactants in groundwater assessment (Abdul et al. 1990 ; Edwards et al. 1991 ).Surfactants in ex situ soil washing process is lessstudied (Deshpande et al. 1999 ; Iturbe et al. 2003 ).The solubilization of PAH is a function of surfactant nature and concentration, washing time, soil/surfac-tant interactions, hydrophobicity (Yeom et al. 1995 ).

Many methods exist to remove organic compounds:surfactant-enhanced solubilization (Lopez et al. 2005 ),solvent-enhanced solubilization (Lee and Hosomi1999 ), chemical oxidation (Flotron et al. 2004 ; Rivas2006 ), biological oxidation (Mulligan 2005). Non ionicsurfactants are well studied (Zhao et al. 2005b ) (Tween80). Anionic/nonionic surfactants mixture are also used

(Zhao et al. 2005b ; Zhou and Zhu 2004 , 2005 ; Zhuand Feng 2003). Various operating conditions govern process efficiency (Deshpande et al. 1999). Researchabout amphoteric surfactants for soil treatment is rare.Among all amphoteric surfactants, betaine structures isvery effective for metallic complexation and oildispersion (Kudaibergenov 2002 ). The use of N-(3-Dodcyloxy-2-hydroxypropyl)-N,N-dimthylgly-cine (DHDG) for pyrene has been shown possible(Guan and Tung 1998).

Metal leaching from soil can be obtained under many conditions: acidic pH (Neale et al. 1997 ),chelators (Peters 1999 ), surfactants/biosurfactants(Mulligan 2005 ), oxidants (Blais et al. 2001 ; Flotronet al. 2004 ). Acids and chelators are often used(Neilson et al. 2003 ). The best metal solubilization

occur with the use of anionic or amphoteric surfac-tant/biosurfactant (acetyltrimtehylammonium bro-mide/surfactin) (Doong et al. 1998 ; Mulligan et al.1999 ). On the opposite, the best surfactants/biosur-factants for hydrocarbons removal, seem to be the nonionic and anionic compounds (Lopez et al. 2005 ) or rhamnolipids (Lafrance and Lapointe 1998 ). Most surfactants are coming from petroleum and appear to be dangerous for the environment. Tween 80 have a pseudo-biodegraded impact on aquatic species(Auriol et al. 2006 ). Alkyl-phenols can pass through-

out wastewater treatment systems and join aquaticenvironment (endocrine disrupting chemicals for fishes (Desbrow et al. 1998 ; Routledge et al. 1998 ).

Flotation is a physico-chemical separation techniquewidely used in mineral ore processing to separate mi-nerals. Flotation is a complex technique related to many parameters: collector type and dosage, conditioningtime and speed, flotation time and air flow, pulp density, pH, temperature, additives, but is also shown as a goodmethod for both organic and inorganic compoundsremoval from polluted soils (Vanthuyne et al. 2003 ;

Zhang et al. 2001). Most of studies about surfactant-enhanced flotation use non ionic (Tween 80, TritonX100) and anionic (SDS) surfactants, but a cationicone (DTAB dodecyl trimethyl ammonium bromide)has been compared to others (Zhang et al. 2001).

Studies about cationic and amphoteric surfactants arevery few and their use is more devoted to cosmeticindustry. The objective of this research was to test andcompare non ionic and amphoteric surfactants for PAHand Pb removal from soil. Soil quality and contamina-tion level were estimated and compared to the regulatory

level in Quebec Canada (MDDEPQ 1999).

2 Methodology

2.1 Soil Samples

Three soils (S1, S2 and S3) coming from confidentialorigins were used in this study. Physical and chemicalcharacteristics of these soils are given in Table 1.

Water Air Soil Pollut


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Humidity was determined according to the method2540B (APHA 1999 ). Total carbon (C), total nitrogen(N) and sulfur (S) were analyzed by a CHNS Lecoanalyser. Granulometry was analyzed using five sievessizes as follows: 2 1 0.5 0.25 0.125 0.0053 mmas described in Mercier et al. ( 2001 ). Phosphorus (P),

calcium (Ca), potassium (K), and sodium (Na)were analysed by ICP-AES as described in Djedidiet al. (2005 ).

For experiments soil samples were passed through a 2mm sieve. The fraction smaller than 2 mm was kept andthen was passed in a quarting apparatus. Table 2 shows

Parameters Units Soils

S1 S2 S3

Humidity % w w1 11.7 11.0 10.7Density g cm

3 2.8 3.2 3.0Particle size %>2 mm 15.8 16.4 27.0

21 mm 15.1 9.4 22.110.5 mm 21.2 17.9 17.10.50.25 mm 21.7 28.2 13.70.250.125 mm 14.1 18.1 9.90.1250.053 mm 6.3 6.7 6.5%


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the PAHs and toxic metals concentrations in the soilsand the limit regulatory levels in Quebec (Canada) for acommercial or industrial soil (criteria C).

2.2 Washing Assays in Erlenmeyer Shake Flasks

All experiments in this section were performed on soilS1 as described in Djedidi et al. ( 2005 ) for the acidleaching part. Assays were carried out on twentygrams of soil for a 10% ( w v1) pulp density at roomtemperature (22 2C). After 60 min of shaking at 175 rpm (Orbital shaker, Lab-line Environ-Shaker,model 3528), soil and washing solutions wereseparated by vacuum (0.5 bar) filtration on Whatman934-AH membrane (pore size=1.5 m). Soil was thendried at 60C, and analyzed for both PAHs andmetals. The influence of drying on a possible

volatilization of lower molecular weight PAHs has been controlled by extracting contaminants on dryand wet materials. No difference was observed for any of all analyzed PAHs.

The performance of different surfactants wasfirstly tested at different concentrations (0.0, 2.5,5.0, 10.0 and 25.0 g of surfactant/kg of dry soil). Brij

35 and Tween 80 were both obtained from AldrichCanada, whereas CAS and BW were bought fromChemRon.

Tween 80 and Brij 35 are non-ionic surfactantswell referenced in literature (Zhao et al. 2005a ).Tween 80 is a polyoxyethylenesorbitan monooleate

consisting in a long esteric chain ended with a big polar cyclic and ramified head and Brij 35 is a polyoxyethylene (23) lauryl ether consisting in analcohol group at the end of a long polyoxyethylenechain. Amphoteric surfactants CAS and BW consist in a long hydrocarbon chain ended respectively withamino-hydroxysultaine (Norton et al. 2005 ) andamino-betaine groups (Stasiuk and Schramm 1996 ).Some important characteristics of used surfactants aregiven in Table 3

In a second time, washing treatment at pH 2 and 3

was studied in presence of CAS (5.0 g kg1

). Addit-ions of sodium chloride (NaCl=5.5 M) at pH 3 andEthylene Diamine Tetra Acetic Acid (EDTA=0.025 M)were also tested in presence of CAS (5.0 g kg

1).EDTA and NaCl were obtained from Merck. The pHadjustment was done using hydrochloric acid (HCl=12 M, Fisher Scientific).

Table 3 Characteristics of the surfactants used in this study

Class Non ionic Amphoteric

Abbreviations Brij 35 Tween 80 CAS BW

Names Polyethyleneglycoldodecyl ether

Polyoxyethylenesorbitanmonooleate

CocamidopropylHydroxysultane

Cocamydopropylbetaine

Molecular.weight.(g mol

1)

1,200 1,310 452 387

Density(g mL

1)1.05 1.00 1.11 1.04

HLB a 16.9 15

CMC (M) b 9.2105 1.210

5 5105 1.810

5

Formula CH 3(CH 2)11

(OCH 2CH 2)n-OH(n=23)

C64 H124 O27 CH3(CH 2)13 N(OH) (CH 2)3-

N+(CH 3)2-CH 2

CHOH

CH 2SO 3

CH 3(CH 2)13 N(OH)

(CH 2)3-N+(CH 3)2-CH 2

CH 2COOHBiodegradability

(%) cunknown + 96% 99%

References (Aldrich 2008 ) (Aldrich 2008 ) (Lucy and Tsang 2000 ) (Stasiuk and Schramm 1996 )

+ Qualitative evidence for biodegradation without presentation of quantitative informationa Hydrophilic lipophilic balance b Critical micellar concentrationc Surfactants biodegradability from Swisher, R.D. ( 1987 )



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2.3 Soil Micellar Solution Separation

The different techniques of micelles separation weretested on soil S1 after 60 min of treatment in presence of 10 g Tween 80 kg

1 of soil and in the conditions previously described. The following separation techni-

ques have been compared: Vacuum filtration (Whatman934-AH membrane) and centrifugation (30 min at 500,1,000, 1,500, 2,000 and 3,000 g ) (Beckmann Coulter Allergra 6). Soil was then collected, dried at 60C,and analyzed for PAHs.

2.4 Flotation Cell Experiments

Experiments were carried out in triplicate using aDenver Lab-1 flotation cell. Soils S2 and S3 weretreated with a 10% pulp density for 1 L total volume.

After a 15 min agitation period at 1,800 rpm, foamswere collected on the top of the cell during a 15min flotation period (air flow=3 L min

1). Condi-tioning and flotation parameters such as time, speed, pulp density were selected from Zhang et al. ( 2001 ).Soil and froth were separated from washing solutions by vacuum filtration (Whatman 934-AH), then driedat 60C, and analyzed for both PAHs and metals.Two washing conditions have been tested: (1) CAS(5.0 g kg

1); (2) CAS (5.0 g kg1) + NaCl (5.5 M) at

pH 3.

2.5 Analytical Techniques

For every batch of analysis, a certified materialreference was used to confirm the extraction methodeffectiveness: BCR no. 524 (obtained from Institutefor Reference Materials and Measurements) for PAHsand PACS2 (obtained from National Research Coun-cil of Canada) for metals. PAHs analysis was performed by GC MS (Perkin Elmer, model Clarus500, with column type of VF-5MS FS 300.25 mm

0.25 m), after a Soxhlet extraction of PAHs from10 g of soil according to a standard protocol(Ministre du developpement durable de l environne-ment et des parcs du Quebec 2001 ) and a solid phaseextraction for PAHs from liquid samples (Ministredu developpement durable de l environnement et des parcs du Quebec 2006 ).

Twenty one compounds were identified in theextracts: naphtalene (NPN), methyl-2-naphtalene

(M2NPN), acenaphtylene (ACyN), acenaphtene(ACN), fluorene (FLU), phenanthrene (PHE), anthra-cene D-10, anthracene (ANT), fluoranthene (FLR), pyrene (PYR), benzo[a]anthracne (BAN), chrysene(CRY), benzo[b+j+k]fluoranthene (BJK), benzo[a] pyrene (BAP), dimethylbenzanthracene (DMBAN),

3-methylcholanthrene (3MCN), benzo[ghi]perylene(BPR), indeno[1,2,3-cd]pyrene (INP), dibenzo[a,h]anthracene (DBA).

One of them labelled with deuterium were used asextraction recovering standards. The average yield for ANT-D10 reaches 89 5%. M2NPN, ACyN,DMBAN and 3MCN were not enough abundant inconsidered soils to be detected by the method. As it was not possible to separate b, j or k benzofluor-anthene and all given values are expressed as a sum of Benzo[b+j+k]fluoranthene. The PAH extraction and

GC

MS operating conditions are the same as de-scribed in Zheng et al. ( 2007 ). Initial temperature isfixed at 80C. A first ramp of heating is maintained at 15.0C.min

1 up to 220C, and a second is set at 5.0C.min

1 until 320C for a total time of analysis in36.33 min. The injection volume is 1.6 L. Analyseswere controlled using a certified solution Mix64(obtained from Supelco). Every sample was injectedin two dilutions in order to follow every compound present in different ranges of concentrations and to better appreciate data. A 30% confidence interval is

given as acceptable for PAHs analysis in the certifiedmaterial (BCR no. 524) and it has always beenrespected during analytic controls (Standard deviationvalues are: NPN 2%, ACyN 3%, CAN 4%, FLU 3%,PHE 2%, ANT 2%, FLR 9%, PYR 10%, BAN 15%,CRY 11%, BJK 11%, BAP 22%, BPR 14%, INP16%, DBA 17%).

Metals analysis was performed by ICP-AES(Varian, model Vista-AX simultaneous ICP-AES)after a complete mineralization of soil according themethod 3030I (APHA 1999 ). Analysis was controlled

using reference certified solutions obtained from SCPscience to assure a confidence interval of around 2%for Ca, Cd, Cr, Cu, Ni, P, Pb and Zn, 1% for Fe and5% for Na.

The pH measurement was done using a pH-meter (Fisher Acumet model 915) equipped with a double- junction Cole-Palmer electrode with Ag/AgCl refer-ence cell. Oxidation reduction potential (ORP) wasmeasured with a platinum electrode.



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3 Results and Discussion

3.1 PAH Removal

Controls of NaCl and EDTA alone have been pursued. No PAH removal was observed without CAS, and the results are not presented. Table 4 givesthe removal yields of all PAHs ( PAH), evaluated on

contaminant concentrations in the soil before and after treatment. Bri j 35 and BW were found to beineffective for PAHs removal. Best PAHs removalyields (62% and 46%) were obtained respectively at surfactant concentration of 10 g kg

1 for Tween 80and 5 g kg

1 for CAS.As shown on Fig. 1, every PAH compound

fluctuated in the same way with an increase of surfactant concentration (Tween 80 and CAS). Duringthe assays with the highest surfactant concentration (25g kg

1), solubilization from soil was decreased for each

PAH compound. This observation witnesses the inter-facial behavior of selected surfactants, and confirms theidea of an optimal concentration for PAHs removalfrom soil. As discussed previously, PAHs solubilizationis maximal around the CMC eff (effective criticalmicelle concentration in soil/aqueous solution). TheseCMC eff values are estimated between 500 and 1,000mg L

1 for Tween 80 and near 500 mg L1 for CAS

and appear, as presented in Table 5, between 31 and 63times higher than CMC for Tween 80 and 24 times for CAS.

The decrease of the PAH solubilization using a highsurfactant concentration (25 g kg

1) can be explained by the interactions occurring during soil washing between water, surfactant, mineral particles, soluble particles, hydrophobic particles, PAH, and metals.Surfactant concentration can influence the type of formed micelles and so that the nature of solubilized particles, as presented in Fig. 2. Depending on itsdosage, surfactant can mainly interact with contami-nants or with soil particles. Thus, it seems that for

concentrations lower than CMC eff (alpha zone onFig. 2) surfactants are not engaged in the solubilizationof any material, and appear as soluble macromoleculesin the medium. Around the CMC eff (bta zone), themain interactions include PAH/surfactant and PAH/ hydrophobic-particles/surfactant, while at higher con-centrations (gamma zone) the equilibrium is moved toincrease surfactant interactions with hydrophobic

0

10

20

30

40

50

60

70

80

90

100

0.0% 0.5% 1.0% 1.5% 2.0% 2.5% 3.0%

0.0% 0.5% 1.0% 1.5% 2.0% 2.5% 3.0%

Tween 80 (% w w -1)

P A H ( m g

k g -

1 )

P A H ( m g

k g -

1 )

0

10

20

30

40

50

60

70

80

90

100

CAS (% w w -1)

PHEATNFLRPYRBANCRY

BJKBAP

PHEATNPYRBANCRYBJKBAPINPFLR

Fig. 1 Residual PAHs concentrations in soil S1 (mg kg1 of dry

soil) after washing in Erlenmeyer shake flasks using different concentrations of Tween 80 and CAS. Reaction time=60 min, pulp density= 10%

Surfactants Surfactant concentration (g kg1)

0.0 2.5 5.0 10.0 25.0

Tween 80 21 146 5917 629 1920Brij 35 23 00 2010 810CAS 2413 462 1836 268BW 00 57 136 263

Table 4 PAH removal(%) from soil S1 using thedifferent surfactants (reac-tion time=60 min, pulpdensity=10%)



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particles and mineral particles. High surfactant con-centrations disadvantage PAH solubilization by con-centrating them into soil. CMC characterizes theconcentration of surfactant at which the first micelleis formed in pure water. Zheng and Obbard ( 2002 )introduced the CMC eff as the concentration at whichthe first micelle is formed in soil/solution system. Theconcentration we are interested in, in this research, isthe concentration at which the solubilization of PAHs

is maximal. This concentration is called C PAHopt , whichis the lowest concentration of surfactant which givesmaximal solubilization of PAHs.

As seen on Table 3, the biodegradability of TW80is still not quantified, while CAS is known to be biodegradable at 96%. Also considering the fact that Tween 80 is a potential toxic molecule (Auriol et al.2006 ), the surfactant CAS has been chosen to developa process for simultaneous removal of PAHs andmetals. Because of their ability to act as anion or

cation depending on pH and salts in presence,amphoteric surfactants like CAS can support manyoperating conditions without precipitating.

As shown in Fig. 3, a decrease of the soil pulp pHto 3 causes a considerable decrease of low (less thanfive aromatic rings) molecular weight PAH removal

(45% to 16%). High molecular weight PAH (morethan five aromatic rings) removal is maintained (45

46%) in these conditions.The addition of 5.5 M NaCl at pH 3 has slightly en-

hanced the removal yield of high molecular weight PAHs(from 45% to 51%). Solubilization of low molecular weight PAH is decreased from 45% to 16% in the casesof both addition of 5.5 M NaCl and 0.025 M EDTA.

As can be seen from Table 2, regulatory thresholdsfor PAHs vary from 100 to 10 mg kg

1 of dry soildepending on the PAH. If regulatory levels (commer-

cial or industrial use of soil) for low molecular weight PAHs, such as NPN, ACN, FLU, PHE, FLR, PYR areusually around 100 mg kg

1, they are reduced to10 mg/kg in the cases of more toxic high molecular weight PAHs, such as BAN, CRY, BAP, BJK, INP,DBA, BPR. For that reason, it seems promising,depending on PAH contamination and objectives of rehabilitation, to use CAS for low molecular weight PAHs removal and/or to use CAS + NaCl to solubilizehigh molecular weight PAHs.

Table 5 Comparison of CMC and CMC eff for Tween 80 andCAS

Surfactants Tween 80 CAS

CMC (mg L1) 16 24

CMC eff (mg L1) 500 1000 500

Ratio (CMC eff /CMC) 31 63 21

Fig. 2 Scheme of different interactions occurring dur-ing CAS-enhanced soilwashing



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3.2 Pb Removal

Pb analysis, carried out during assays with CAS,suggests some solubilization of Pb (215%) (Fig. 3).This result illustrates the existence of mixed micellesPb CAS PAH as presented on Fig. 2. If the tail of CAS can interact with PAH and hydrophobic materialas a result of hydrophobic affinity, the aminosultainefunctional group on its head can also interact with

mineral material or metal ions, creating coordinatecovalent and ionic interactions with it.

Assays at pH 2 and 3 were firstly done in presence of CAS (results for assays at pH 2 are not shown becauseof the ineffectiveness of these conditions) and wereshown as ineffective for Pb removal. At low pH (pH 3),CAS is mainly present in its cationic form (R-N +(CH 3)2-CH 2 CHOH CH 2SO3H), and as a matter of fact Pbsolubilization is decreased from 215% to 44%(Fig. 3). This observation confirms the existence of mixed micelles with CAS, which are inhibited under

acidic conditions, due to the loss of the negative chargeof the polar functional group of the surfactant.

If pH decrease was shown as ineffective for Pbremoval, NaCl and EDTA addition appears as goodenhancers allowing an increase of Pb removal from21 5% for CAS (5 g/kg) treatment to respectively555% and 3512% for NaCl (5.5 M) and EDTA(0.025 M) treatments. The improved Pb solubilizationobserved in presence of salts, is due to the formation of metallic complex: chloro-complexes (PbCl + , PbCl 2

0,

PbCl 3, PbCl 4

2), or EDTA-complex ([Pb(EDTA)] 2,

[Pb(HEDTA)], [Pb(H 2EDTA)]) depending on the

salt added (Djedidi et al. 2005 ). Assays with saturated NaCl (5.5 M) solution were maintained at pH 3 (for maximal lead chloro-complexes stability) and revealthat even in its cationic form, CAS is involved in

mixed micelles (Pb chloro-complexes

CAS

PAH).

3.3 Separation Techniques

3.3.1 Centrifugation

Centrifugation has been tested at different centrifugalforces (500, 1,000, 1,500, 2,000, and 3,000 g ) toseparate soil from washing solution and was comparedto filtration (1.5 m pore size membrane). Figure 4shows that filtration is a more efficient solid/liquid

separation technique than centrifugation (at 500 g ) for the separation of the PAH-surfactant micelles from thesoil particles. No PAH removal was observed at thehigher centrifugal force than 500 g (results not shown).

Under centrifugal force, micelles may readsorb tosoil particles. In fact, solubilized PAH in surfactant micelles can easily be separated from soil particles sincemicelles in aqueous phase can pass through the filter.Centrifugation, even at low speed, pelleted out micellesfrom aqueous phase, and takes the micelles back into

solid phase giving a decrease of separation efficiency(Zheng et al. 2007 ). Even if less than occurring duringcentrifugation, the concept of contaminants readsorp-tion to soil during filtration, is still maintained, for that reason flotation assays were pursued.

3.3.2 Flotation

Flotation assays have been carried out with CAS andCAS + NaCl + pH 3 on soils S2 and S3. Particleremoval (solids in froth), presented in Table 6, is

calculated as a ratio between the amount of dry frothcollected (FM) and the amount of initial dry soilintroduced (FC). This parameter varied from 4% to9% with soils and tested conditions.

Preliminary flotation assays under saline condi-tions have revealed that 97% of the solids collected infroth were composed of NaCl. Sodium was measuredin each part of the process: 311% are collected infroth rinsing water (FMR) and 6710% in soil rinsingwater (FLR). No sodium has been detected in froth

0%

10%

20%

30%

40%

50%

60%

70%

Total PAH PAH < 5 rings PAH > 5 rings Pb

R e m o v a l

( % )

ControlCASCAS + pH 3CAS + NaCl + pH 3CAS + EDTA

Fig. 3 PAHs and Pb removal yields (%) from soil S1 after washing in Erlenmeyer shake flasks using different conditions(CAS, CAS + pH 3, CAS + NaCl + pH 3 and CAS + EDTA).Reaction time=60 min, pulp density=10%



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after rinsing, whereas 1.2% of added salt has beenmeasured in soil after complete treatment (FS).

PAHs and metals removal presented in Table 6 aregiven as a weight ratio between the part of contaminantswashed (FC FS) from soil and their initial amount (FC). For the two soils treated, NaCl addition seems toimprove PAHs removal as much as Pb removal.

Removal yields were also generally superior for soilS2 treatment in comparison to soil S3. This can beexplained by the granulometry (particle size: S2


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takes place during process operation. This loss canresult from the possible solubilization of mineral

particles of soil at low pH, but can also be due tothe different operations (transfers) done during soiltreatment. This loss of weight imposes to evaluate theremoval performance, not as a decrease of concen-

trations in soils before and after treatment, but as adecrease of the amount of pollutants (in mg) in soil between initial and final steps of washing processusing flotation.

The particles removal in froth (11%) combinedwith the potential solubilization of mineral particles

(8%) cause a recovery of 82% of the initial mass of soil in the treated fraction. This mass decrease cancreate a concentration of pollutants in soil during the process, depending on the particles mainly floated.

Although all PAHs are recovered in solid phases,only 65% of Pb are found to be present in thesefractions (18% for FM and 47% for FS). However, Pbremoval was estimated around 54%. This confirmsthe idea that Pb is mainly solubilized by complexation

PHE FLR BAN CRY BJK BAP INP BPR

Soil S2

Soil S2

0

1020

30

40

50

60708090

100

110

120

PHE FLR BAN CRY BJK

P A H ( m g

k g -

1 )

P A H ( m g

k g -

1 )

FCFS

FCFS

0

20

4060

80

100

120140

160

180

200

220

Fig. 5 Residual PAH concentrations in soils S2 and S3 (mgkg

1 of dry soil) and respect of criteria C after flotation usingthe (CAS + NaCl + pH 3) condition. Reaction time=15 min, pulp density= 10%

Table 7 Mass balance of solids, and concentrations of PAHsand Pb in the different fractions resulting of the treatment of thesoil S3 (after flotation using CAS + NaCl + pH 3 condition(reaction time=15 min, pulp density=10%, [CAS]=5.0 g kg

1,[NaCl]=5.5 M, pH 3))

Parameters Mass or

volume(g or L)

PAH

(mg kg1

)

Pb (mg kg1)

Initial soil (FC) 89.0 1 050 580Treated soil (FS) 72.7 757 333Froth (FM) 9.3 4,580 983First and second

rinsing of FS (FLR)1.6


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with chloride ions. Pb analysis in the leachatesvalidates the presence of 37% of Pb in FLR, 2% inFMR. Pb can eventually precipitate in part with CAS,a specific study could be done to test this hypothesis.Previous studies (Djedidi et al. 2005 ; Mercier et al.1996 ), have shown with chemical equilibrium soft-

ware (MINEQL) that the formation of chloro-complexes increases dramatically the solubility of Pb at acidic pH when a high concentration of chloride ismaintained. However, it is not possible without performing a particular sophisticated experiment todemonstrate that ion exchange is not playing a role asthe high chloride concentration implies strong ionexchange driving force.

Soil washing using flotation under CAS and NaClconditions seems to be a promising method to treat soils contaminated with both organic and inorganic

pollutants. This is presented as a process scheme onFig. 6. The main interest of the method results in thefact that the process is done simultaneously in thesame reactor. Two distinct concentrated phases areobtained after treatment: one solid phase (FM) mainly polluted with PAHs, and the leachates (FLR + FMR)mostly contaminated with metal ions. If solid wastesare intended to be managed to waste disposal site, avalorization of them as carbon source for bioremedi-ation or combustion in cement factory should beencouraged. Metal removal from leachates must be

studied to allow their reuse in a final process.Precipitation or electrochemical treatments appear as potential good techniques to treat these leachates.Because of the high conductivity of the soil leachates,Pb electrodeposition is proposed as an appropriatetreatment (Drogui et al. 2007 ).

4 Conclusions

Polluted soils and brownfields constitute a major

problem, in this fact that it impacts the health of theglobal environment and human beings. Because of thelack of economical technology to treat these soils,they often are managed in landfills. This paper demonstrates the use of an amphoteric surfactant (CAS) in soil washing processes. CAS has a simplechemical structure and is largely used in the cosmeticindustry. This study has shown that CAS has theability to form mixed micelles with organic (PAH)and inorganic (Pb) contaminants.

Salts (NaCl and EDTA) have been shown to wellenhance Pb solubilization. Flotation has been tested asa separating technique to concentrate PAH in frothwhile the aqueous solution contains the metals. Thiscombination implies good results for both PAH andPb removal from soil. Flotation appears as a promis-

ing technique for soil treatment under selectedconditions. The suggested process for organic and/or inorganic removal would not be considered as optimalat this state. Some research works should be done tooptimize the operating conditions and the perfor-mance of the process. Finally, to pursue this project, it is required to develop a method for the treatment of soil leachates.

Acknowledgments This project was funded by FQRNT andMontreal Center for Brownfield Rehabilitation. Theauthorswould

like to express their gratitude to Pauline Fournier, Myriam Chartier and Typhaine Schmitt for their technical assistance.

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