Aquifer washing by micellar solutions: 1: Optimization of alcohol–surfactant–solvent solutions

Ž .Journal of Contaminant Hydrology 29 1998 319–346

Aquifer washing by micellar solutions:1 Optimization of alcohol–surfactant–

solvent solutions

Richard Martel a,b,), Pierre J. Gelinas b, Jacques E. Desnoyers cá INRS-Georessources, 2535, boul. Laurier, C.P. 7500, Sainte-Foy, Qc., Canada G1V 4C7´

b GREGI, Department of Geological Engineering, LaÕal UniÕersity, Quebec, Qc., Canada G1K 7P4ć ÍNRS-Energie et Materiaux, 1650 BlÕ. Lionel Boulet, C.P. 1020, Varennes, Qc, Canada J3X 1S2´

Received 6 June 1996; revised 9 February 1997; accepted 19 February 1997

Abstract

Phase diagrams were used for the formulation of alcohol–surfactant–solvent and to identify theŽ .DNAPL Dense Non Aqueous Phase Liquid extraction zones. Four potential extraction zones of

Mercier DNAPL, a mixture of heavy aliphatics, aromatics and chlorinated hydrocarbons, wereidentified but only one microemulsion zone showed satisfactory DNAPL recovery in sand

Ž .columns. More than 90 sand column experiments were performed and demonstrate that: 1neither surfactant in water, alcohol–surfactant solutions, nor pure solvent can effectively recover

Ž .Mercier DNAPL and that only alcohol–surfactant–solvent solutions are efficient; 2 adding saltsto alcohol–surfactant or to alcohol–surfactant–solvent solutions does not have a beneficial effect

Ž .on DNAPL recovery; 3 washing solution formulations are site specific and must be modified ifŽ .the surface properties of the solids mineralogy change locally, or if the interfacial behavior of

Ž . Ž .liquids type of oil changes; 4 high solvent concentrations in washing solutions increaseŽ .DNAPL extraction but also increase their cost and decrease their density dramatically; 5

maximum DNAPL recovery is observed with alcohol–surfactant–solvent formulations whichŽ .correspond to the maximum solubilization in Zone C of the phase diagram; 6 replacing part of

surfactant SAS by the alcohol n-butanol increases washing solution efficiency and decreases theŽ .density and the cost of solutions; 7 replacing part of n-butanol by the nonionic surfactant HOES

Ž .decreases DNAPL recovery and increases the cost of solutions; 8 toluene is a better solvent thanŽ .D-limonene because it increases DNAPL recovery and decreases the cost of solutions; 9 optimal

alcohol–surfactant–solvent solutions contain a mixture of solvents in a mass ratio of toluene to

) Corresponding author.

0169-7722r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved.Ž .PII S0169-7722 97 00029-6

( )R. Martel et al.rJournal of Contaminant Hydrology 29 1998 319–346320

D-limonene of one or two. Injection of 1.5 pore volumes of the optimal washing solution ofn-butanol–SAS–toluene–D-limonene in water can recover up to 95% of Mercier DNAPL in sandcolumns. In the first pore volume of the washing solution recovered in the sand column effluent,

Žthe DNAPL is in a water-in-oil microemulsion lighter than the excess aqueous phase Winsor.Type II system , which indicates that part of the DNAPL was mobilized. In the next pore

volumes, DNAPL is dissolved in a oil-in-water microemulsion phase and is mobilized in an excessŽ .oil phase lighter than the microemulsion Winsor Type I system . The main drawback of this oil

extraction process is the high concentration of ingredients necessary for DNAPL dissolution,which makes the process expensive. Because mobilization of oil seems to occur at the washingsolution front, an injection strategy must be developed if there is no impermeable limit at theaquifer base. DNAPL recovery in the field could be less than observed in sand columns because ofa smaller sweep efficiency related to field sand heterogeneities. The role of each component in theextraction processes in sand column as well as the Winsor system type have to be better definedfor modeling purposes. Injection strategies must be developed to recover ingredients of thewashing solution that can remain in the soil at the end of the washing process. q1997 ElsevierScience B.V. q 1998 Elsevier Science B.V.

1. Introduction

This study is part of a 4 year research project aiming to achieve the development ofsurfactant solutions which could restore contaminated soils by the in situ dissolution of

Ž .DNAPLs Dense Non Aqueous Phase Liquid . The DNAPLs from the contaminated siteŽ .at Ville Mercier, Quebec Martel, 1988 , provide a good case of complex heavy organics´

Žrepresenting a challenge for restoration technologies. Previous studies Desnoyers et al.,.1983a; Martel et al., 1993; Martel and Gelinas, 1996 show that surfactant solutions´

containing both alcohols and surfactants can be used for the efficient miscible displace-Ž Ž .ment of mixtures of petroleum and organic compounds TCE 1,1,2,2-tetrachloroethane ,

Ž . .PCE 1,1,2,2,-tetrachloroethylene , diesel, gasoline, etc. present at residual saturation incontaminated soils. Dissolution of the organic contaminants results from the formation

Ž .of oil-in-water microemulsions Martel and Gelinas, 1996 in a Winsor Type I system´Ž . Ž .Winsor, 1954 . Interfacial tension IFT measurements between microemulsion andNAPL phases show that IFT is not ultra-low. Under these conditions, NAPL dissolutioncan occur without its mobilization. For the efficient displacement of heavy and viscousoils, such as those at Mercier, an organic solvent must be added to the alcohol–surfac-

Ž .tant system Martel et al., 1993 . Phase diagrams are used to select system componentsfor the efficient dissolution of Mercier DNAPL. This selection phase is followed bydissolution and oil recovery tests in sand columns which are performed to optimize theselected system. Other complementary laboratory measurements were done to check thecompatibility of the chosen solution with the aquifer materials. The effect of salinity onDNAPL recovery was also investigated.

Ž .The objectives of this paper are 1 to select, through phase diagrams, washingŽ .solutions able to dissolve Mercier DNAPL, and 2 to optimize these solutions and

verify the effect of different variables on extraction efficiency of DNAPL by performingresidual DNAPL recovery tests in sand columns. Companion papers examine the process

Ž .responsible for DNAPL recovery Martel, R., et al., 1998a and describe a field pilotŽ .application of the technology Martel, R., et al., 1998b .

( )R. Martel et al.rJournal of Contaminant Hydrology 29 1998 319–346 321

2. Mercier site characterization

Between 1968 and 1980, an estimated 40 000–160 000 m3 of petroleum sludges andother organic liquid wastes were dumped in an abandoned gravel pit, which is part of a

Ž .fluvio-glacial complex near Ville Mercier Quebec about 30 km southeast of Montreal´Ž .BAPE, 1995 . At that time, the liquid wastes in the lagoons were observed to separate

Ž . Ž y3 .into four distinct phases: a LNAPL Light Non Aqueous Phase Liquid 930 kg m atŽ y3 .the surface, an aqueous phase 1100 kg m with dissolved organic compounds in the

Ž y3 .middle, a lower DNAPL 1300 kg m , and a heavy organic mud at the bottom of theŽ .lagoons Poulin, 1977 . From 1975 to 1981, the wastes in the lagoons were pumped out

and treated, but more than 1000 m3 of DNAPL had already infiltrated into the sand–Ž .gravel and the underlying fractured rock aquifers Martel, 1988 .

For the present laboratory study, samples of Mercier DNAPL were taken frommonitoring wells near the lagoons in 1992. Mercier DNAPL is like a crude oil which haslost its natural volatile compounds and contains up to 16% of chlorinated solventsŽ .mainly 1,2-dichloroethane, 1,1,2-trichloroethane, tetrachloroethene, trichloroethene, etc.Ž . y3Table 1 . It has a density of 1050 kg m , and at 88C it is 18 times more viscous than

Ž . Ž y1 .water 25 mPa s . Interfacial tension between Mercier DNAPL and water 14 mN m isŽsignificantly lower than the expected IFT between pure solvents and water 30–

y1 .35 mN m , which suggests that Mercier DNAPL already contains some surfactiveingredients. In the Mercier sands, DNAPL wets carbonate sand grains, as indicated by

Žthe small contact angle of a DNAPL drop on a calcite crystal cut on the cleavage.plane . Mercier DNAPL also wets quartz locally, as indicated by the variable contact

Ž .angle measured on a quartz crystal cut and polished perpendicular to the c-axis . Thesetwo minerals are predominant in the Mercier sands and gravels.

Field observations suggest that chemical and physical properties of the DNAPL maychange with time and location. As shown in Fig. 1, most of the liquid waste is stilllocated below and close to the former lagoons. Near the source area, DNAPL flowsvertically through the sand and gravel aquifer, then it follows the top of a low-permea-bility till, to finally penetrate the fractured bedrock aquifer through windows in the till

Table 1Physical properties and chemical composition of typical Mercier DNAPL

DNAPL Composition

38% Aliphatics and alicyclics28% Aromatics16% Chlorinated solvents12% Asphaltenes6% Resins

Ž .Physical properties 88C

Viscosity: 25mPasy3Density: 1048kgm

y1Ž .Interfacial tension DNAPL–water : 14mNmŽ .Contact angle DNAPL–water–calcite : 0–78

Ž .Contact angle DNAPL–water–quartz : 2–908


Ž Ž ..Fig. 1. Cross-section of NAPL distribution at the Mercier site adapted from BAPE 1995 .

unit. More than 1 million m3 of soil and fractured bedrock were contaminated at a levelŽ .mostly under residual oil saturation GREGI, 1992 .

Since 1984, a pump-and-treat system has prevented off-site migration of contami-nated ground water by creating and maintaining a hydraulic trap. However, no signifi-

Ž .cant amount of NAPL was removed from the aquifer or the source area Martel, 1988 .Technologies would be available to clean up or confine the lagoon area but because ofthe large volumes of polluted solid material and the depth of the contaminated zoneŽ .between 20 and 40 m , excavation and off-site treatment can hardly be done economi-cally. In situ steam injection cannot be used either because of the high viscosity of the

ŽMercier DNAPL. Steam injection is limited to oils with viscosities under 5.6 cP Stewart.and Udell, 1988 . Innovative in situ technologies must therefore be developed for the

Ž .clean-up of the deeper contaminated zone sand–gravel and fractured rock aquifers . Insitu soil washing with micellar solutions is one of the technologies which is potentiallyapplicable.

3. Micellar solutions optimization

Ž .Optimization of micellar washing solutions can be done in different ways Table 2 .Advantages and disadvantages of optimization by salt, alcohol or solvent additions, aswell as by the increase of surfactant concentration, are discussed.

3.1. Changing salinity

In petroleum engineering, surfactant solutions are usually optimized by observingŽ .phase behavior and constructing phase diagrams Lake, 1989 . This process involves the


Table 2Advantages and disadvantages of washing solution optimization techniques

Advantages Disadvantages

Salting surfactant —increases oil solubilization —preflush with saltysolution water required

—no Mercier DNAPLdissolution

Increase surfactant —increases oil solubilization —limited by its waterconcentration solubility

—no preflush with salty water —increases its adsorption—creates pore-blockingemulsions—causes local viscousinstability—can decrease injectivity—no Mercier DNAPLdissolution

Adding alcohol to —increases oil solubilization —decreases surfactant andsurfactant solution resulting miroemulsion

viscosity—no preflush with salty water —eliminates exclusion of polymer

from the microemulsion phases—may not mobilize oil —no significant Mercier DNAPL

dissolution—can inject high ingredientconcentrations—decreases surfactant adsorption

Salting alcohol– —no significant advantage —may destabilize the solutionsurfactant solution

—decreases interfacial tensionand can favor mobilization of oil—decreases efficiency of surfactantin solubilizing oil—increases the viscosity of themicroemulsion-phase—no significant MercierDNAPL dissolution

Adding solvent to —dissolves and mobilizes —injection of large volume ofalcohol–surfactant Mercier DNAPL and other washing solution to preserve optimalsolution complex DNAPLs condition and prevent separation

of surfactant–alcohol–solvent—expensive process—limited choice of biodegradablesolvents

determination of the number and composition of phases in thermodynamic equilibriumfor specific concentrations of surfactant, brine, and oil. Three classical types of phase

Ž . Ž .behaviors are observed Winsor, 1954 Fig. 2 :1. at low brine salinity, under the binodal curve, the mixture splits into two phases; a

Žlower phase microemulsion oil-in-water microemulsion containing brine, surfactant,


Ž Ž ..Fig. 2. Phase behavior in Winsor system types adapted from Lake 1989 .

.and some solubilized oil and an excess oil phase containing traces of brine andsurfactant. This system is known as a Winsor Type I system. The tie lines within thetwo-phase region have negative slopes and the plait point P is located close to theR

oil apex. Solubilization of oil-in-water and hence the drop size of oil-in-waterincrease with increasing salinity, i.e. as repulsion between the charged head group ofthe surfactant increases. The IFT between phases is low, normally above0.01 mN my1.

2. At higher salinity, electrostatic forces decrease surfactant solubility in the aqueousphase. Under the binodal curve, the mixture splits into two phases consisting of an

Župper-phase microemulsion water-in-oil microemulsion containing most of the sur-.factant and some solubilized brine and an excess brine phase. This system is known

as Winsor Type II. The tie lines within the two-phase region have positive slopes andthe plait point P is located close to the brine apex. Water-in-oil microemulsion dropL

size and brine solubilization in oil decrease with increasing salinity, i.e. withdecreasing repulsion between head groups of the surfactant. In this case, IFT usuallyexceeds 0.01 mN my1.

3. At intermediate salinities, a three-phase mixture consisting of a middle-phase mi-Ž . Žcroemulsion, an excess oil phase as in Type I , and excess brine phase as in Type

.II is called a Winsor Type III system. In this system, IFT between the microemul-Ž y3sion and oil and between microemulsion and water are both ultra-low 10 –

y4 y1.10 mN m , and the salinity at which both IFTs are equal is called the ‘optimum’salinity. Optimal salinity may be found by comparing the phase volume of equili-

Žbrated oil and the surfactant solution. Phase behavior with DNAPL denser than. Žbrine instead of oil may change the position of the different phases Baran et al.,


.1994 . For example, in a Type II system, water-in-DNAPL microemulsion may bethe lower phase.Changing any condition which enhances the oil solubility of surfactant will cause a

Ž . Ž .shift from Winsor Type I to Type II Table 2 . These changes may involve: 1 type andŽ . Ž . Ž . Ž .concentration of surfactant; 2 temperature; 3 addition of a cosurfactant alcohol ; 4

Žchanging oil composition making the oil more polar makes it a better solvent for the..surfactant; Puerto and Reed, 1983 .

3.2. Increasing surfactant concentration

High surfactant concentrations increase solubilization of oil but have some draw-Ž . Ž .backs: 1 concentration is limited by its water solubility; 2 adsorption is more

Ž .important for high concentrations; 3 high concentrations create pore-blocking emul-Ž . Ž .sions; 4 high concentrations cause local viscous instabilities during a displacement; 5

high concentrations can decrease injectivity owing to a high viscosity of surfactantŽ .resulting from the formation of liquid crystals or condensed phases Lake, 1989 .

3.3. Adding an alcohol

Alcohol can cause the transition between systems to occur at a different salinityŽ . Ž .Type I to Type II because a water-soluble alcohol short chain length causes the

Ž .surfactant to be more water soluble Trushenski et al., 1974 whereas a high molecularŽ .weight alcohol causes an increase in oil solubility Salter, 1977 . The presence of

Ž .alcohol can have many effects: 1 it can decrease surfactant and resulting microemul-Ž . Ž .sion phase viscosities Healy and Reed, 1974 ; 2 it can decrease surfactant adsorption

Ž .Trushenski et al., 1974 by filling surface sites which might be occupied by surfactantŽ . Ž .Lake, 1989 ; 3 it eliminates exclusion of polymer from the microemulsion phase at

Žlow surfactant concentration if the polymer and the surfactant are incompatible opposite. Ž .charge Trushenski, 1977 . Injection of an alcohol–surfactant solution for aquifer

restoration does not require a preflush with salty water to preserve optimal salinityconditions in the surfactant slug.

Previous work shows that the combination of alcohols and surfactant to dissolve lightŽ . Žoil gasoline and diesel or solvents TCE, PCE, BTEX, Benzene, Toluene, Xylenes,

.Ethylbenzene, etc. is more effective than the use of either alcohols or surfactantsŽ .separately Desnoyers et al., 1983a; Martel et al., 1993 . Complete dissolution of

residual diesel saturation in a Winsor Type I system was achieved in sand columns withan n-butanol or n-pentanol–anionic surfactant solution. No bulk mobilization of diesel

Ž .was observed in these downward washing experiments Martel and Gelinas, 1996 , as a´high IFT between diesel and the washing solution was maintained. Unfortunately, thesealcohol–surfactant solutions cannot dissolve significant quantities of heavy and viscous

Ž .oils such as creosote, motor oil, or Mercier DNAPL Martel et al., 1993 .

3.4. Changing salinity of alcohol–surfactant solutions

Salinity optimization is not always advantageous for alcohol–surfactant solutionsŽ . Ž .because salt can: 1 destabilize the solution; 2 decrease interfacial tension and favor


Ž .mobilization of oil for salinity up to optimal; 3 decrease the oil solubilizing efficiencyŽ . Ž .of the surfactant Salter, 1978 ; 4 increase the viscosity of the microemulsion phase to

values greater than that of the oil phase for salinities lower or greater than the optimalŽ .Salter, 1977 .

3.5. Adding a biodegradable solÕent in alcohol–surfactant solution

Ž .Previous work on tar sand extraction Desnoyers et al., 1983b; Sarbar et al., 1984shows that bitumen can be dissolved if a light organic solvent is added to alcohol–surfactant mixtures. These systems were studied in detail through pseudo-ternary phase

Ž .diagrams Desnoyers et al., 1983b and studied in parallel with extractions of bitumenŽ .from tar sands Sarbar et al., 1984 . A shift in Winsor system type may occur if solvent

is added because the solvent tranfers in the oil phase and changes its composition. Aconsiderable volume of washing solution must be injected into the aquifer to preserve

Ž .optimal conditions because: 1 the different behavior of the components in surfactant–Ž .cosurfactant–solvent solutions leads to separation of ingredients; 2 dilution occurs

Ž .Martel et al., 1997a .

4. Experimental procedures

4.1. Phase diagrams

Phase diagrams establish the extent of the single phase zone identifying the possibleconcentrations of alcohol–surfactant and solvent which can be combined in a washing

Ž .solution. With four components alcohol, surfactant, water, and solvent phase diagramsare treated as pseudo-ternary systems by keeping the alcoholrsurfactant ratio constant.The curve separating the single-phase zone from the multiple-phase zone is obtained by

Ž .the cloud point technique Desnoyers et al., 1983a . At the boundary between the twozones, a clear solution becomes milky owing to the formation of a microphase. Thisturning point is observed visually. For an aqueous alcohol–surfactant solution with aconcentration of a%, the maximum concentration of solvent which can be miscibly

Ž .combined is b% Fig. 3 . The best solvent to use with a given alcohol–surfactantsolution must have a lower curve close to the water–solvent axis, and a single-phasezone wide enough to allow a high surfactant–alcohol concentration. The zone of interestfor aquifer restoration is in the water-rich region of the phase diagram because, inaquifers, water saturation is much higher than oil saturation.

Phase diagrams were established to select alcohol–surfactant–solvent mixtures whichcan be used to solubilize Mercier DNAPL. These diagrams represent five components:water, Mercier DNAPL, solvent, alcohol and surfactant. There are various ways ofreducing this system to a pseudo-ternary system. The most practical approach is to fixthe mass fraction of water, alcohol and surfactant, and call this pseudo-component

Ž .‘active matter in water’ Fig. 4 . The phase diagrams containing Mercier DNAPL, theŽ .solvent and active matter in water Fig. 4 can be easily correlated with the previous

Ž .pseudo-ternay diagram with alcohol–surfactant, water and solvent Fig. 3 . In Fig. 3, anŽ .active matter in water value a is chosen along the axis alcohol–surfactant:water.1


Fig. 3. Pseudo-ternary phase diagram and concentration range for alcohol–surfactant–solvent washingsolution.

When a solvent is added to the active matter, the composition is moving along thedashed line a –solvent in Fig. 3 or along the axis a –solvent in Fig. 4. For phase1 1

Ž .diagram construction including the DNAPL Fig. 4 , the solvent is added to the activeŽ .matter in water a to give mixtures Z which are titrated with Mercier DNAPL, along1

the dashed lines Z–DNAPL. The selected solutions for sand column experiments havecomposition Z. All diagrams were done at 88C and concentrations are expressed in percent by mass. The cloud point technique cannot be used to establish phase diagramswhen one of the components is opaque oil, such as Mercier DNAPL. However, thevarious states of the system can be determined by observation of the mixture andespecially from the preferential wetting of the phases on the walls of the cell.Alcohol–surfactant–solvent–water phase diagrams were drawn in the water-rich regionwith Mercier DNAPL. Four zones were identified by using this method.

Ž Ž .. Ž .In Zone A Fig. 5 a , oil in black aggregates like ashes is suspended in a clearamber emulsion, or in a beige emulsion. Oil aggregates stick on glass walls of the vialand on Teflon-coated magnets. Oil adhesion occurs during stirring or when the emulsion

Fig. 4. DNAPL extraction zones in phase diagrams with the selected washing solution.


breaks. After the emulsion breaks, oil stays separate from the original emulsion and doesnot form an emulsion again after stirring. DNAPL forms a deposit on the bottom of thebottle. Because only partial dissolution of Mercier DNAPL is observed in Zone A, oilrecovery is expected to be low during washing experiments in sand columns.

Ž . Ž . Ž . Ž .Fig. 5. DNAPL extraction zones observed in phase diagrams a Zone A; b Zone B; c Zone C; d Zone D.


Ž Ž ..Zone B Fig. 5 b is a relatively stable emulsion zone. The fine oil-in-water emulsionis amber or sometimes coarser beige–amber and slightly more cloudy. A ring ofunattached amber droplets is observed at the liquid interface with air when the emulsionis spread on the glass walls of the vial. Without stirring, the emulsion begins todestabilize after a few hours and after 10 h breaks down in two phases. A weak stirringof the two separated phases brings the oil back into emulsion. Zone B is of potentialinterest for Mercier DNAPL recovery.

Ž Ž ..Zone C Fig. 5 c is a DNAPL-in-water microemulsion zone. This amber mi-Žcroemulsion was observed for high alcohol–surfactant concentrations more than 15% of

.alcohol–surfactant in water . Generally, in Zone C up to 5% of Mercier DNAPL can bedissolved. This zone is desirable for remediation because it is the closest to a truesolution.

Ž Ž ..Zone D Fig. 5 d is characterized by a coarse, cloudy, beige unstable emulsion ofDNAPL-in-water. A ring of attached amber droplets is observed at the liquid limit whenemulsion is spread on the vial’s glass wall. Preferential adherence of one phase wasobserved on the test tubes glass wall when wetted by the emulsion.

4.2. Sand column experiments

Ž .The sand column used contained 128 g of Mercier sand Fig. 6 . This sand isŽ .composed of several mineral species 62% carbonates, 34% quartz, and 4% feldspar .

Clay- and silt-size particles, which represent 5% of the material in the sand, wereremoved to prevent column clogging. Particle sizes varied from 63 mm to 4 mm. The

Ž . 2 y1mean grain diameter d was 0.6 mm, the specific surface area was 0.006 m g and50Ž Žthe natural organic carbon content was 0.57% Walkey–Black method Agriculture

..Canada, 1977 . As clay minerals are absent and organic carbon content is very low,removing the fine fraction is not likely to affect remediation greatly. Fine removal wasused to facilitate laboratory procedures. The sand column had a mean hydraulic

Ž . y4 y1conductivity of 1.6"0.7 =10 m s and a mean porosity of 0.34"0.01. All sandŽ .column tests were done using the following procedure: 1 after filling and compaction

Ž .with Mercier sand, CO was injected and deaerated water was introduced; 2 downward2Ž y1 .injection of about 5 g of Mercier DNAPL at high velocity 354"33 cm h pushed by

Fig. 6. Experimental setup for sand column washing.


0.5 l of deaerated water was done to reach a residual DNAPL saturation of 10.7"3.7%Ž . Ž .volume ; 3 downward injection of three pore volumes of washing solution with aperistaltic pump was carried out at a Darcy’s velocity of 5.25"0.92 cm hy1. Themasses of DNAPL leaving the column after saturation, transported in the effluent, andremaining in the soil sample after washing were determined by spectrophotometryŽ .HACK DRr200, Loveland, Colorado at 550 nm. Dichloromethane was used as asolvent for mass determination of DNAPL. With this technique, DNAPL mass balancein the sand column is determined with a precision of "6%. Downward washing wasselected because the displacement front is more stable when a light and viscous washing

Ž .solution is displacing water Lake, 1989 .

4.3. Density and Õiscosity of washing solutions, fine particle dispersion and surfactantprecipitation

The viscosity and density of washing solutions are physical properties influencingDNAPL recovery. Solution density was measured with a pycnometer and the viscositywith a Cannon–Fenske viscometer. During field injection, surfactant solutions maymobilize fine mineral particles which can clog the porous media and restrict groundwa-

Ž .ter flow Muecke, 1979 or can make the handling or treatment of the recovered effluentdifficult. Polyvalent cations adsorbed on sediment particles can precipitate surfactants

Ž .and reduce the efficiency of the washing solutions Somasundaran et al., 1984 .Turbidity measurements of the washing solution put into contact with the aquifer

Ž .material are used to quantify these two phenomena. Surfactant solutions 35 ml are putinto contact with 5.0 g of the Mercier aquifer material in a 40 ml vial. After a 5 minmechanical mixing period, the vial is left at rest for a 24 h period, the supernatant is thenextracted and the turbidity of the solution is measured using the nephelometric method.

ŽThe upper limit is 200 NTU for the equipment used HACH 18900-10, Loveland,.Colorado .

4.4. Interfacial tension measurements

Ž .Interfacial tension IFT was measured to identify the Winsor system type in whichDNAPL recovery occurred. IFT between the aqueous and oil phases was measured by

Ž ..the spinning-drop method University of Texas, Model 300; Cayias et al., 1975 . TheŽVonneguth cylindrical approximation was used for the calculation of IFT Adamson,

.1976 . Various washing solutions were put in contact with solvents or Mercier DNAPLin solvents in a mass ratio of 1:1. After thorough mixing, the solutions were left tostabilize for a 24 h period. In some cases, when surfactant solutions and oil phasesformed stable emulsions, they were centrifuged at 3900 rev miny1 during an additional

Ž .4–5 h Hermle model Z360K, Germany . The density of each phase at equilibrium wasŽ .measured with a flow densimeter vibratometer Sodev-03D, Rockforest, Quebec with a

precision of "0.01 kg my3. After an equilibration time of 5–10 min in the tensiometer,the diameter of the spinning-drop is monitored at 5 min intervals until it remainsconstant within "0.001 cm for at least three consecutive readings and an inflection pointis observed in the data. During IFT measurements, the temperature of the tensiometercapillary tube varied from 248C to 308C. Readings of the spinning-drop at two


temperatures for one liquid system allowed data to be corrected for temperaturevariations. The precision of the IFT measurement was "0.01 mN my1.

5. Results

More than 100 phase diagrams were constructed and 90 sand column experimentswere run during this phase of the project. The most significant results are presented here.

5.1. Initial selection of alcohols, surfactants, and solÕents

Abbreviation, chemical composition, and relative cost of surfactants, alcohols, andsolvents used in this study are presented in Table 3. Based on an optimization study of

Žalcohol–surfactant mixtures for light oil solubilization Martel et al., 1993; Martel and. ŽGelinas, 1996 two alcohol–surfactant solutions n-BuOH–SAS and n-AmOH–LRO in´

.a mass ratio of 1.0 were initially selected for phase diagram construction with fiveŽ Ž . Ž . Ž . .solvents toluene Tol , xylenes Xyl , ethylbenzene Etbz , acetal, and D-limonene at

88C. Table 4 presents a flow chart of the washing solution selection and optimizationprocess used in this study. Solvents as well as alcohols and surfactants were selectedbased on their miscibility in Mercier DNAPL, their potential biodegradability, and

Ž .relatively low toxicity Gregoire, 1994 . The n-BuOH–GEN solution was also selected´Ž .because Genagen CAB an amphoteric surfactant has a head group charge which varies

with the pH of the solution and this may potentially affect DNAPL recovery. A solutionof n-BuOH–GENAM was used to verify the effect of a cationic surfactant on DNAPLrecovery. A nonionic surfactant, HOES, was tested to replace part of the alcohol orincrease the proportion of surfactant in the washing solution. A branched alcohol,

Table 3Abbreviations of selected surfactants, alcohols, and solvents with their relative cost

y1ŽTrade name Abbreviation Chemical compound Cost $CANkgŽ . .all sodium salts of ingredients

Surfactantsa Ž .Genepol LRO anionic LRO Lauryl alcohol ethersulfate 7.92a Ž .Hostapur SAS anionic SAS Secondary alcane sulfonate 3.74

a Ž .Hoes 4004 nonionic HOES C rC ethoxylate with 7 EO 3.6812 14a Ž .Genagen CAB amphoteric GEN Alkyl amidopropyl betane 14.10a Ž .Genaminox LA cationic GENAM Lauryl dimethyl aminoxide 12.88

Linear alcoholsŽ .n-Butanol n-BuOH CH CH OH 1.803 2 3

Ž . Ž .n-Amyl alcohol 1-pentanol n-AmOH CH CH OH 3.853 2 4Ž . Ž .Iso-butanol i-BuOH CH CH CH OH 2.282 2 2

SolÕentsToluene Tol C H 0.807 8

Xylenes Xyl C H 1.328 10

Ethylbenzene Etbz C H 5.038 10

D-Limonene D-lim C H 7.0510 16a Ž . Ž .Hostafluid V4120 acetal Ace CH CH OC H 9.023 2 5 2

a Trade mark of Hoechst Inc.


Tab

le4


i-BuOH, was used to verify the effect of alcohol type on DNAPL dissolution. Otherfactors, not covered here, are related to the reuse and treatability of ingredients of thewashing solution. These are of primary importance for field applications.

5.2. Phase diagrams for alcohol–surfactant–solÕent formulation and for identificationof DNAPL extraction zones

The alcohol–surfactant–solvent–water mixtures must form a single phase in theporous media to avoid separation of ingredients, which causes modification of the ratiosand a decrease in the DNAPL solubilization efficiency. Before performing any sandcolumn experiment, phase diagrams are developed to determine the amount of solventwhich can be combined with the alcohol–surfactant solution.

Toluene, a C aromatic hydrocarbon, is a good solvent in combination with n-8Ž .BuOH–SAS. This solvent shows a curve close to the water–solvent axis Fig. 7 .

However, the single-phase zone is so narrow that surfactant–alcohol concentrations arelimited and the possible proportion of solvent in the washing solution is small. Usingsolvents with higher equivalent carbon atom numbers such as D-limonene, a C10

terpene, and acetal, a C ether, increases both the maximum injectable alcohol–surfac-6Žtant concentration and the possible proportion of solvent in the washing solution Fig.

.7 . However, these solvents are less easily dissolved by the alcohol–surfactant solution.

5.3. Rejected solutions

As shown in Table 4, no sand column experiments were performed with n-AmOH–LRO and Tol, Xyl or Etbz, as they show very high dispersion of fine particles orsurfactant precipitation when these washing solutions are mixed with Mercier sand.Concentrations of DNAPL in these solutions are also difficult to determine because theyform stable emulsions with dichloromethane. Only a low concentration of n-AmOH–LRO is possible with these solvents. Because n-BuOH–GENAM becomes very viscous

Ž .and unstable at laboratory temperature 258C , this solution is not recommended for sandcolumn experiments. Alcohol–surfactant–acetal mixtures were not used because they do

Ž . Ž .not emulsify Zone B nor dissolve Zone C Mercier DNAPL. Only Zone A or D can

Fig. 7. Extension of the microemulsion zone in the phase diagram with the selected solvents.


be observed with this solvent. i-BuOH–SAS–Tol solutions were discarded because avery small Zone B is observed with Mercier DNAPL. Other alcohol–surfactant mixturessuch as n-AmOH–SAS, or n-AmOH:HOES–SAS were tried, to increase solubilizationof Tol, Etbz or Xyl, but single-phase zones were too small to be useful. Ingredientproportions of some selected solutions for sand column experiments with MercierDNAPL are presented in Table 5.

5.4. Interfacial tension lowering

Mercier DNAPL already contains surface active products. In fact, without theŽ y1 .addition of surfactant, IFT between Mercier DNAPL and water 14 mN m is lower

Ž y1 .than for typical oil or solvent and water values 30–35 mN m . IFT measurementsbetween dark DNAPL and washing solution are difficult with the spinning-droptechnique. The black oil phase must be lighter than the aqueous phase in the spinningtest tube. However, when a solvent or variable proportion of Mercier DNAPL in the

Ž .solvent e.g. toluene is put in contact with an alcohol–surfactant solution, IFT betweenthe oil and aqueous phase is almost similar. IFT is stable when Mercier DNAPL

Ž .contains up to 75% of solvent Fig. 8 . In fact, IFT behaves similarly when variousconcentrations of n-AmOH–LRO or n-BuOH–SAS in water are put in contact with

Ž Ž ..toluene or 75% of toluene in Mercier DNAPL Fig. 9 a , so IFT between washingsolution and toluene is a good approximation of IFT between washing solution andMercier DNAPL. As shown, IFT decreases as ingredient concentrations increase. For thewashing solution tested, which has alcohol–surfactant concentrations between 15% and20%, IFT ranges between 0.2 and 0.7 mN my1, which is typical of a Winsor Type I orWinsor Type II system. Replacing toluene by D-limonene in the washing solution will

Ž Ž ..increase IFT Fig. 9 b . However, higher alcohol–surfactant concentrations can beobtained with D-limonene, with IFT reaching the same level. Partial replacement ofn-butanol by the nonionic surfactant, HOES, or replacing SAS by an amphotericsurfactant, GEN, did not change IFT significantly. For the washing solution tested,

Ž .decrease of IFT is as follows: n-BuOH–SASsn-BuOH:HOES 2:1 –SASsn-BuOH–GEN)n-AmOH–LRO.

5.5. Sand column experiments

More than 90 Mercier DNAPL recovery tests in sand column were performed toverify the effect of different variables on DNAPL extraction and to optimize washing

Table 5Ingredient proportions of some selected washing solutions for sand column tests

Solution n-Butanol SAS HOES D-Limonene TolueneaŽ . Ž . Ž . Ž . Ž .concentration % concentration % concentration % concentration % concentration %

E 5.725 5.725 – – 4.580F 10.180 10.180 – 18.590 –J 7.070 10.605 3.535 15.160 –GG 9.205 9.205 – 13.16 13.16II 8.335 8.335 – 8.330 8.330MM 9.500 9.500 – 11.88 11.88

aConcentrations of ingredients are in mass fraction in water.


Fig. 8. Interfacial tension between different proportions of toluene in Mercier DNAPL and the solution ofŽ .n-AMOH–LRO 15% active matter in water .

solutions. The impact of solvent, residual oil saturation, water velocity and direction,salinity, and sand mineralogy were studied. Optimization was done by changing the typeand the proportion of alcohol–surfactant and solvent which can provide differentDNAPL extraction zones.

5.5.1. Effect of different Õariables

5.5.1.1. Effect of solÕent. Neither a surfactant solution, an alcohol–surfactant solution,nor a pure solvent, such as D-limonene, can effectively recover the DNAPL in sand

Ž .columns Fig. 10 . However, an alcohol–surfactant–solvent mixture can recover close to85% of residual DNAPL saturation in Mercier sand after the circulation of a single porevolume.

5.5.1.2. Effect of initial residual DNAPL saturation and reproducibility of sand columntests. Three DNAPL recovery experiments in sand column were performed two or three

Ž .times to verify the reproducibility of the results Fig. 11 . These tests also allow us toverify that a 50% variation in initial residual DNAPL saturation in sand columnsŽ .solution F has no significant effect on DNAPL recovery.

5.5.1.3. Effect of flow direction and Õelocity. Upward or downward flow of the washingŽ .solution in the column does not influence DNAPL recovery Fig. 12 . A slower

Ž .circulation half normal velocity of washing solution increases contact time and favorsŽ Ž ..a better dissolution of DNAPL also observed by Abriola et al. 1995 . Dissolution

kinetics may be an important factor to consider in a field application of the technology.

5.5.1.4. Effect of salinity. To verify if salinity influences Winsor system types andDNAPL recovery, salted washing solutions were put in contact with Mercier DNAPL.

ŽFor the salinities tested in cells, no shift in Winsor system types is observed from.Winsor Type I to Type II or Type III but more DNAPL seems to be dissolved in the

equilibrated aqueous phase as salinity increases. However, a limited amount of salt can


Ž .Fig. 9. a Interfacial tension between toluene or 75% toluene in Mercier DNAPL and various concentrationsŽ .of n-AmOH–LRO or n-BuOH–SAS in water. b Interfacial tension between toluene, D-limonene, and

various concentrations of alcohol–surfactant in water.

be combined with the different washing solutions because salts decrease their miscibilityand can produce undesirable two-phase washing solutions. Sand column tests wereperformed with washing solutions salted close to their miscibility limit. When saltsŽ . Ž .NaCl or CaCl are added to an n-BuOH–SAS in water solution Fig. 13 , no DNAPL2

recovery is observed. For washing solutions with solvents, sodium orthosilicate de-creased DNAPL recovery in both cases. Addition of salt makes the DNAPL extraction

Ž .zone less favorable, going from Zone B to Zone A in phase diagrams Solution O . Salts


Fig. 10. Effect of washing solution formulation on DNAPL recovery in sand column.

in alcohol–surfactant or in alcohol–surfactant–solvent solution do not have beneficialeffects on DNAPL recovery.

5.5.1.5. Effect of mineralogy. Mercier DNAPL is more difficult to recover in quartz sandŽ . Ž .Ottawa sand than in carbonate-rich Mercier sand Fig. 14 . The decrease in recoverycannot be explained by permeability differences of the sands because Ottawa sand has ahydraulic conductivity lying between the those of the two Mercier sands tested. We canexpect that DNAPL recovery in the fractured quartzitic bedrock at Mercier aquifer willbe more difficult than in the carbonate-rich sand, not only because of the complex flowbehavior in a fractured medium but also because of the matrix mineralogy.

The DNAPL wetting of the mineral surfaces was observed on Mercier and OttawaŽ .sand grains maintained between two glass plates micromodel . A layer of sand was put

between two glass plates which were also glued on their edges with epoxy to form aconfined porous medium. Two needle tips were installed at the inlet and outlet of theglass plates for the circulation of fluids. As for sand column tests, CO , water, and2

Ž .Fig. 11. Effect of initial residual DNAPL saturation on DNAPL recovery in sand column Solution F andŽ .reproductibility of washing experiments in sand column Solutions GG and J .


Fig. 12. Effect of flow direction and velocity on DNAPL recovery in sand column.

DNAPL were injected in the micromodel. DNAPL drops on sand grains were observedŽ .with a microscope Lietz Ortholux II POL-MK, Leatzwetzlar, Germany and photo-

Ž .graphed with a camera Wild MP 551, Meerbrugg, Switzerland connected to aŽ .photometer Wild Photoautomat MPS 45, Meerbrugg, Switzerland . At residual satura-

Ž . Ž Ž ..tion, DNAPL wets quartz grains Ottawa sand locally Fig. 15 a . The injection of thewashing solution recovers most of the DNAPL but residues stick to quartz surfaces after

Ž Ž ..water rinsing Fig. 15 b . In Mercier sand, no DNAPL residues are observed afterinjection of the same washing solution. Thus, the optimal washing solutions may vary

Ž .depending on the mineralogy of the media sand or fractured bedrock to be cleaned.Washing solution formulation is site-specific and must be modified if surface properties

Ž .of the solids mineralogy change locally or if the interfacial behavior of the liquidsŽ .type of oil changes.

5.5.2. Washing solution optimizationWashing solutions were optimized at 88C by circulating washing solutions downward

in Mercier sand columns. The optimization aims to increase the efficiency of washing

Fig. 13. Effect of salted washing solution on DNAPL recovery in sand column.


Fig. 14. Effect of mineralogy and permeability on DNAPL recovery in sand column.

solutions, keeping their density as close as possible to water density, and their viscosityand cost as low as possible. For a washing solution lighter than water, its circulation isdifficult to accomplish close to the aquifer floor. Upward buoyancy forces, which act onthe washing solution, are proportional to the difference in fluid density between thewashing solution and water. However, permeability anisotropy of the fluvio-glacialsands at Mercier favors a preferential horizontal flow and minimizes the buoyancyeffects created by the density contrast between water and the washing solution. Viscouswashing solutions create viscous instabilities in porous media and longer periods of timeare required for the injection of solutions in the field.

Ž .Fig. 15. Residual DNAPL saturation in a water-saturated quartz sand trapped between two glass plates: aŽ .before washing experiment; b after washing experiment.


5.5.2.1. Changing DNAPL extraction zone. Sand column experiments were performedwith washing solutions representing the four extraction zones of the phase diagrams.Washing solutions were selected in the different zones based on the maximum solubi-lization or emulsification efficiency observed. As expected from the behavior of Zone Asolutions in phase diagrams, insignificant DNAPL recovery is obtained from sand

Ž Ž ..column tests with these solutions Fig. 16 a . With solutions in Zone B, DNAPLrecovery in sand column is good. Sand column experiments show a much better DNAPLrecovery when the solvent proportion in the washing solution corresponds to themaximum solubilization efficiency in Zone C of the phase diagram. In Zone D, thewashing solution is unstable because solvent concentration is above the miscibility limitand the DNAPL extraction is low.

ŽFor all extraction zones, marginal DNAPL recovery in sand columns mass of.DNAPL recoveredrmass of ingredients is much higher than the marginal DNAPL

extraction predicted by phase diagrams because phase diagrams predict the amount ofŽ Ž ..DNAPL solubilized or emulsified, but not mobilized Fig. 16 b . Marginal DNAPL

recovery in sand columns decreases with pore volume of solution recovered because theDNAPL available in the sand decreases as the washing experiment proceeds. This

Ž .Fig. 16. a Effect of DNAPL extraction zones identified in phase diagram on DNAPL recovery in sandŽ .column tests. b Marginal DNAPL solubilization or emulsification in different extraction zones of phase

diagrams compared with marginal DNAPL recovery in sand column tests.


phenomenon cannot be predicted by phase diagrams, as no porous media is present inthe cells in which the liquids are at equilibrium. For the quantity of washing solutioninjected in the sand column, marginal DNAPL recovery never reached the marginalsolubilization because DNAPL is also mobilized. In Zones B, C, and D, the first porevolume of recovered effluent was a water-in-NAPL microemulsion phase and an excesswater phase in a Winsor Type II system. The second and third pore volumes containedan NAPL-in-water phase and an excess LNAPL phase characteristic of a Winsor Type Isystem. In Zone A, as no solubilization of DNAPL occurs, the three-pore volumes are awater-in-NAPL phase and excess water phase in a Winsor Type II system. A detaileddescription of recovered phases from a sand column experiment with an optimal solution

Ž .in Zone C of the phase diagram has been presented by Martel et al. 1997a .

5.5.2.2. Changing the solÕent proportions. Increasing n-BuOH–SAS concentrationallows more D-limonene to be combined in the washing solution and thus increases the

Ž .solventr alcoholqsurfactant ratio. An increase in the proportion of solvent increasesŽ .the Mercier DNAPL extraction in sand columns Fig. 17 . The effect of solvent

proportion was verified with D-limonene. Obviously, the better DNAPL recovery isrelated also to the increase in the n-BuOH–SAS concentration in the washing solution.The best solution has 50% of D-limonene and can recover more than 85% of the

Ž .residual DNAPL saturation after the circulation of 1.5 PV pore volumes or 90% after3.0 PV. The main drawbacks of using only D-limonene as a solvent in the washingsolutions are: the large ingredient concentrations required, the high cost of the solutions,

Ž y3 .and their low densities 903 kg m for the best solution . A 40% D-limonene propor-tion in the washing solution recovers only 70% of DNAPL in sand columns after the

Ž y3 .circulation of 1.5 PV. This solution is also too light 927 kg m and too expensive. Acombination of solvents must be tested.

5.5.2.3. Replacing D-limonene by toluene. Because D-lim is expensive, sand columntests were done to replace it by other ingredients. Toluene is a better solvent than

Ž .D-limonene for Mercier DNAPL recovery Fig. 18 . However, the proportion of Tolwhich can be combined with n-BuOH–SAS is limited, whereas D-lim concentration can

Fig. 17. Effect of D-limonene proportion in washing solutions on DNAPL recovery in sand column.


Ž .be very high more than 50% . When D-lim is combined with Tol, the washing solutionmay contain higher solvent proportions than with the use of Tol alone. Washingexperiments were performed with solutions containing Tol and D-lim in variableproportions. For all these experiments, the mass ratio of alcoholrsurfactant was keptconstant at 1.0. The increase in the proportion of toluene increases DNAPL recovery and

Ždecreases the amount of solvent required to obtain extraction conditions in Zone C Fig..18 . For a TolrD-lim ratio of 1.0 and for optimal conditions in Zone C of the phase

diagram, 90% of the DNAPL is recovered after the injection of 1.5 PV. The optimalŽ y3 .solution is less expensive and denser 953.6 kg m than solutions which used only

D-limonene. For a TolrD-lim ratio of 2.0, a recovery rate of 87% is obtained. Thissolution has a density of 961.6 kg my3 and its cost is lower than the optimal solution at a

Ž .TolrD-lim ratio of 1.0 Table 4 . The lower proportion of solvent in the solutionincreases its density and viscosity.

In the following tests, one ingredient was replaced by another by keeping the molarfractions of other ingredients of the solution as constant as possible.

5.5.2.4. Replacing SAS by n-BuOH. A less expensive solution which contains a 30%mass fraction of D-limonene was used to verify the effect of alcohol proportions. Thesolution cost is decreased when n-BuOH replaces part of SAS. Replacing SAS by

Ž .n-BuOH n-BuOHrSAS ratios go from 1.0 to 2.5 increases the washing solutionefficiency and decreases its viscosity, but also decreases its density, from 941.3 to

y3 Ž . Ž930.7 kg m Fig. 19 . With the optimal solution shown above TolrD–lim ratio of.2.0 , DNAPL recovery is increased when the n-BuOHrSAS ratio goes from 1.0 to 1.5.

However, the density of the solution is decreased from 961.6 kg my3 to 956.8 kg my3

and the solution is unstable at laboratory temperature.

5.5.2.5. Replacing n-BuOH by a nonionic surfactant. Oil and polychlorinated biphenylsŽ .PCBs have been recovered in aquifers with a low concentration of a surfactant

Ž .equivalent to HOES Abdul et al., 1990, Abdul et al., 1992 . Because it is a nonionicŽ .surfactant, it plays the same role as an alcohol Martel et al., 1993 . Replacing 3.1%

Fig. 18. Effect of toluenerD-limonene proportion in washing solution on DNAPL recovery in sand column.


Fig. 19. Effect of n-BuOHrSAS ratio on DNAPL recovery in sand column.

Ž . Ž .molar fraction 18% mass fraction of n-BuOH by a nonionic surfactant HOESŽ .decreases DNAPL recovery Fig. 20 . HOES will not be used in the optimal solution

because it is also much more expensive than n-BuOH.Laboratory experiments show that n-butanol–SAS–D-limonene–toluene solution in

water can recover more than 95% of Mercier DNAPL in sand columns after theinjection of 3 PV. In the first pore volume of washing solution injected, the DNAPLseems to be mobilized in a Winsor Type II system, whereas in the next pore volumes,DNAPL is dissolved in a Winsor Type I system. The main drawback of this oilextraction process is the high concentration of active matter necessary for DNAPLdissolution, which makes the process expensive. The role of each component in theextraction process in sand column as well as the Winsor system type has to becharacterized. In the field, a polymer solution must be injected behind the washing

Žsolution to push it and to obtain a good sweep of the contaminated formation Martel,.1995 . The formulations of the washing solutions that need more tests at a larger scale

are presented in Table 6. Detailed results of large-scale experiments are presented in aŽ .companion paper Martel, R., et al., 1998a . Injection strategy must take into account the

Fig. 20. Effect of a nonionic surfactant on DNAPL recovery in sand column.


Table 6Selected washing solutions for Mercier DNAPL recovery recommended for experiments at larger scale

y3n-BuOHrSAS TolrD-lim n-BuOHqSASr Ingredient Density Viscosity $CANmy3Ž . Ž .mass ratio mass ratio TolqD-lim concentration kg m mPas

Ž .mass ratio in water %

Ž .1 1.0 1.0 0.7 44.73 953.6 10.3 1471.5Ž .2 1.0 2.0 0.9 41.30 961.6 10.3 1124.2

aŽ .3 1.5 2.0 0.8 40.05 956.8 17.8 1052.5

aUnstable at 258C.

fact that the density of the selected solutions is smaller than water density, and thatbuoyancy forces can play an important role during recovery.

6. Conclusions

Phase diagrams were used for the formulation of alcohol–surfactant–solvent washingsolutions and for the identification of the DNAPL extraction zones. Four potentialextraction zones of Mercier DNAPL were identified but only one zone of microemulsionshowed satisfactory DNAPL recovery in sand columns. More than 90 sand column

Ž .experiments were performed and demonstrate that: 1 neither surfactant in water,alcohol–surfactant solutions, nor pure solvent can effectively recover Mercier DNAPL

Ž .and that only alcohol–surfactant–solvent solutions are efficient; 2 adding salts toalcohol–surfactant or to alcohol–surfactant–solvent solutions does not have a beneficial

Ž .effect on DNAPL recovery; 3 washing solution formulations are site specific and mustŽ .be modified if the surface properties of the solids mineralogy change locally, or if the

Ž . Ž .interfacial behavior of liquids type of oil changes; 4 high solvent concentrations inwashing solutions increase DNAPL extraction but also increase their cost and decrease

Ž .their density dramatically; 5 maximum DNAPL recovery is observed with alcohol–surfactant–solvent formulations which correspond to the maximum solubilization in

Ž .Zone C of the phase diagram; 6 replacing part of surfactant SAS by the alcoholn-butanol increases washing solution efficiency and decreases the density and the cost of

Ž .solutions; 7 replacing part of n-butanol by the nonionic surfactant HOES decreasesŽ .DNAPL recovery and increases the cost of solutions; 8 toluene is a better solvent than

D-limonene because it increases DNAPL recovery and decreases the cost of solutions;Ž .9 optimal alcohol–surfactant–solvent solutions contain a mixture of solvents in aTolrD-lim mass ratio of one or two.

Injection of 1.5 PV of optimal washing solutions with n-butanol–SAS–toluene–D-limonene solution in water can recover up to 95% of Mercier DNAPL in sand columns.In the first pore volume of the washing solution recovered in the sand column effluent,the DNAPL is in a water-in-oil microemulsion lighter than the excess aqueous phaseŽ .Winsor Type II system , which indicates that part of the DNAPL was mobilized. In thenext pore volumes, DNAPL is dissolved in an oil-in-water microemulsion phase and in

Ž .an excess oil phase lighter than the microemulsion Winsor Type I system . One couldexpect that the DNAPL recovery rate is overestimated in the column study by usingfreshly contaminated material, whereas the contaminants in real, aged spills have had a


long time to diffuse into, for example, dead-end pores or fractures in the grains.However, the Mercier sands and gravels are of glacial origin with very low weathering.The volume of DNAPL diffused in the matrix would be insignificant relative to theDNAPL in the intergranular pore space. The main drawback of this oil extractionprocess is the high concentration of ingredients necessary for DNAPL dissolution, whichmakes the process expensive. Because mobilization of oil seems to occur at the washingsolution front, an injection strategy must be developed if there is no impermeable limitat the aquifer base. DNAPL recovery in the field could be less than observed in sandcolumns because of a smaller sweep efficiency related to field sand heterogeneities. Therole of each component in the extraction processes in sand column as well as the Winsorsystem type have to be better defined for modeling purposes. Injection strategies must bedeveloped to recover ingredients of the washing solution that can remain in the soil atthe end of the washing process.

Acknowledgements

ŽThis project is funded by the DESRT program Development and Demonstration of.Site Remediation Technology of the Quebec Ministry of Environment and Fauna, and´

Environment Canada. Special thanks go to the students who helped in the laboratoryŽmanipulations Lucie Gauthier, Mireille Lapointe, Genevieve Pomerleau, Nathalie Roy,`

´ .Karl-Eric Martel, and Laurent Saumure . Thanks also go to the research assistants:Pierrette Vaillancourt, Catherine Blais, and Rene Dufault. Special thanks are due to´

´Francois Quirion from INRS-EnergierIMI for his guidance in interfacial tensionmeasurements and for stimulating discussions.

References

Abdul, A.S., Gibson, T.L., Rai, D.N., 1990. Selection of surfactants for the removal of petroleum productsŽ .from shallow aquifers. Ground Water 28 6 , 920–926.

Abdul, A.S., Gibson, T.L., Ang, C.C., Smith, J.C., Sobczynski, R.E., 1992. In situ surfactant washing ofŽ .polychlorinated biphenyls and oils from a contaminated site. Ground Water 30 2 , 219–232.

Abriola, L.M., Pennell, K.D., Pope, G.A., Dekker, T.J., Luning-Prak, D.J., 1995. Impact of surfactant flushingon the solubilization and mobilization of dense nonaqueous-phase liquids. ACS Symp. Ser. 594, 10–23.

Adamson, A.W., 1976. Physical Chemistry of Surfaces. Wiley, New York, 668 pp.Agriculture Canada, 1977. Manuel de methodes d’echantillonnage et d’analyse des sols. Comite canadien de´ ´ ´

pedologie. Soil Research Institute, Ottawa, Ont., 233 pp.´BAPE, 1995. Restauration du lieu contamine de Mercier. Bureau d’audiances publiques sur l’environnement.´

Ministere de l’environnement et de la faune du Quebec, Quebec, Canada, 187 pp.` ´ ´Baran, J.R., Pope, G.A., Wade, W.H., Weerasoorlya, V., Yapa, A., 1994. Microemulsion formation with

Ž .chlorinated hydrocarbons of differing polarity. Environ. Sci. Technol. 28 7 , 1361–1366.Cayias, J.L., Schecter, R.S., Wade, W.H., 1975. The measurement of interfacial tension via the spinning drop

technique. Adsorption at interfaces. ACS Symp. Ser., 8.Desnoyers, J.E., Quirion, F., Hetu, D., Perron, G., 1983a. Tar sand extractions with microemulsions: I—The´

dissolution of light hydrocarbons by microemulsions using 2-butoxyethanol and diethylmethylamine ascosurfactants. Can. J. Chem. Eng. 61, 672–679.

Desnoyers, J.E., Sarbar, M., Lemieux, A., 1983b. Tar sand extractions with microemulsions II: The dispersionof bitumen in microemulsions. Can. J. Chem. Eng. 61, 680–688.

GREGI, 1992. Aquifer Decontamination for Toxic Organics: The Case Study of Ville Mercier, Quebec.´


Hydrogeological Study, Final Report, Vol. 2. Submitted to Environment Canada, Wastewater TechnologyCenter, Burlington, Ont., File 052 SS.KE405-8-6001, 200 pp.

Gregoire, F., 1994. Biodegradabilite relative des detergents Hostapur SAS, Genapol LRO, Phenylsulfonate´ ´ ´ ´HSR et Hoes 4004 de la compagnie Hoechst, des solvants xylene, ethylbenzene, toluene, D-limonene et` ´ ` `Hostafluid v 4120, et des alcools butane-1-ol et pentane-1-ol. Ministere de l’Environnement et de la Faune`du Quebec, Direction des politiques du secteur industriel, Quebec, Canada, 23 pp.´ ´

Healy, R.N., Reed, R.L., 1974. Physicochemical aspects of microemulsion flooding. SPE J. 1974, 491–501.Lake, L.W., 1989. Enhanced Oil Recovery. Prentice–Hall, Englewood Cliffs, NJ, 550 pp.Martel, K.E., 1995. Utilisatien de solutiens de polymeres pour ameliorer l’efficacite de balayape des solutiens´ ´ ` ´ ´ ´

tensioactives developpees pour la resatauratien d’aquiferes contamines aux hydrocarbures immiscibles´ ´ ´ `lounds. These de maıtrise, Departement de geologie et de genie geologique, Universite Laval, Quebec,ˆ ´ Ćanada, 119 p.

Martel, R., 1988. Groundwater contamination by organic compounds in Ville Mercier: new developments. In:Demonstration of Remedial Technologies for Contaminated Land and Groundwater, Bilthoven, Nether-lands, NATOrCCMS 2nd Int. Conf., 7–11 November 1988, pp. 144–177.

Martel, R., Gelinas, P.J., 1996. Surfactant solutions developed for NAPL recovery in contaminated aquifers.´Ž .Ground Water 34 1 , 143–154.

Martel, R., Gelinas, P.J., Desnoyers, J.E., Masson, A., 1993. Phase diagrams to optimize surfactant solutions´Ž .for oil and DNAPL recovery in aquifers. Ground Water 5 5 , 789–800.

Martel, R., Lefebvre, R., Gelinas, P.J., 1998a. Aquifer washing by micellar solutions: 2—DNAPL recovery´mechanisms for an optimized alcohol–surfactant–solvent solution. J. Contam. Hydrol. in press.

Martel, R., Gelinas, P.J., Saumure, L., 1998b. Aquifer washing by micellar solutions: 3—Field test at the´Ž .Thouin sand pit L’Assomption, Quebec, Canada . J. Contam. Hydrol. in press.´

Muecke, T.W., 1979. Formation fines and factors controlling their movement in porous media. J. Pet. Technol.1979, 144–150.

Poulin, M., 1977. Groundwater contamination near a liquid waste lagoon, Ville Mercier, Quebec. M.Sc.´Thesis, University of Waterloo, Ont., 158 pp.

Puerto, M.C., Reed, R.L., 1983. A three-parameter representation of surfactantroilrbrine interaction. SPE J.1983, 669–682.

Salter, S.J., 1977. The influence of type and amount of alcohol on surfactant–oil–brine phase behavior andproperties. Paper SPE 6843, presented at 52nd Annual Fall Tech. Conf. of the SPE, Denver, CO, 9–12October, Society of Petroleum Engineers, Richardson, TX.

Salter, S.J., 1978. Selection of pseudo-components in surfactant–oil–brine–alcohol systems. Paper SPE 7056,presented at 5th Symp. on Improved Methods for Oil Recovery, SPE Meeting, Tulsa, OK, 16–19 April,Society of Petroleum Engineers, Richardson, TX.

Sarbar, M., Brochu, C., Boisvert, M., Desnoyers, J.E., 1984. Tar sand extractions with microemulsions andemulsions. Can. J. Chem. Eng. 62, 267–277.

Somasundaran, P., Celik, M., Goyal, A., Manev, E., 1984. The role of surfactant precipitation and redissolu-tion in the adsorption of sulfonate on minerals. SPE J. 1984, 233–239.

Stewart, L.D., Udell, K.S., 1988. Mechanisms of residual oil displacement by steam injection. SPE Reserv.Eng. 1988, 1233–1242.

Trushenski, S.P., 1977. Micellar flooding: sulfonate–polymer interactions. In: Shah, D.O., Schecter, R.S.Ž .Eds. , Improved Oil Recovery by Surfactant and Polymer Flooding. Academic Press, New York, pp.555–573.

Trushenski, S.P., Dauben, D.L., Parrish, D.R., 1974. Micellar flooding–fluid propagation, interaction andmobility. SPE J. 1974, 633–642.

Winsor, P.A., 1954. Solvent Properties of Amphiphilic Compounds. Butterworths, London.

Documents

Aquifer washing by micellar solutions: 1: Optimization of alcohol–surfactant–solvent solutions