COLLOIDSANDSURFACES A

Colloids and SurfacesA: Physicochemical and Engineering Aspects 177 (2001) 235-246ELSEVIER

www.elsevier.nl{\ocate/colsurfa

L. Zhang a, P. Somasundaran a,*, V. Ososkov b, C.C. Chou b. Henry Krumb School of Mines, Room 911, O>lumbia University, 500 W, 12Oth Street, New York, NY 10027, USAb Center for Environmental Engineering and Sciences, New Jersey Institute of Technology, Newark, NJ 07102, USA

~--

Abstract

Application of flotation for the removal of hydrophobic compounds from soils was studied. Bench scale flotationtests were conducted on artificially contaminated soil, using both a conventional mechanically agitated machine anda flotation column. Flotation parameters tested include collector type, conditioning time, flotation time, surfactantdosage, pulp pH, solid/liquid ratio in conditioning and pulp temperature. It was found that, with conventionalflotation, 74% removal of the contaminant was achieved from soil particles in the range of 75-830 ~; with columnflotation up to 800/0 of oil could be removed from the 250-830-~ soil fraction, and 65% from the 75-830-~mfraction. Flotation was found to have considerable potential for cleaning up contaminated soils. ~ 2001 ElsevierScience B. V. All rights reserved.

Keywords: Soil cleaning; Flotation; Column Hotation; Decontamination; Remediation; Hydrophobic

1. Introduction well as to minimize their resorption on soil parti-cles. The surfactant dosage used is normally in therange of 0.5-2%. In such cases, surfactant regen-eration has to be a part of the process, if costs areto be kept reasonable. In spite of some recentinvestigation, which demonstrated 70-800/0 sur-factant recovery by hexane extraction or ultrafil-tration [3], regeneration methods are not efficientenough for practical applications. Another limita-tion of soil washing is the formation of stableemulsions of contaminants and fine soil particles.Breaking of these emulsions can add to the cost ofremediation significantly. When the soil containslarge fraction of silts and clay particles, soil wash-ing becomes particularly ineffective. Soil washingis ineffective also in treating soil contaminatedwith mineralized metal ions.

Soil contamination caused by organic pollu-tants poses a major problem to the environment.Various processes have been developed in the pastto remove the organic contaminants from the soil.Among them soil washing is a promising technol-ogy. This process includes separation of contami-nated fines from coarse fractions andsolubilization of the contaminants with the aid ofsurfactants [1,2]. However, in this process thedosage of the surfactant has to be very high(significantly above its critical micelle concentra-tion) in order to solubilize the contaminants as

* Corresponding author. Tel.: + 1-212-8542926; fax: + I212-8548362.

E-mail address: ps24@columbia.edu (P. Sornasundaran).

0927-7757/01/$ - see front matter 02001 Elsevier Science B.V. All rights reserved.

PO: 50927-7757(00)00670-1

L. Zhang et oJ. / CoUoids and surfaces A: Physicochem. Eng. Aspects 177 (2001) 235-246236

2. Experimental

2.1. Soil preparation

The soil used in this study was obtained froman unpaved parking area on the New Jersey Insti-tute of Technology (Newark, NJ) campus. Afterdrying the original soil, the desired size fractionwas separated by sieving and sedimentation andagain dried. The soil sample was then artificiallycontaminated by mixing it with solvent refinedparaffin oil (from Ivax Industries, Inc.) dissolvedin hexane and the hexane then removed by evapo-ration. This paraffin oil has very low volatility.This minimizes losses by volatilization during theflotation and analytical procedures. The oil con-tent in the soil after contamination was 1%.

2.2. Reagents

Sodium dodecylsulfate (SDS) and dode-cyltrimethyl ammonium bromide (DT AD) werepurchased from Fluka Chemicals. Pentaethoxy-lated nonyl phenol (NP-5) was from NikkoChemicals, Japan and Triton X-IOO from UnionCarbide. Pine Oil was obtained from ArizonaChemical Co. and Na2CO3 and NaOH were fromFisher Scientific Inc. Tap water was used through-out the study.

2.3. Flotation (mechanically agitated cell)

Flotation was carried out in a Denver 0-1Flotation machine with a flotation cell volume of1.5 1 and impeller diameter of 7.3 cffi. The slurrywas prepared for each run by mixing givenamounts of soil with water in the flotation cell.The pulp was then conditioned for the desiredduration with collector and pine oil and flotationconducted for a given time. After flotation wascompleted, the floats and the sinks were analyzedfor the oil content.

Since most organic contaminants are hydropho-bic, it is possible to separate them from uncon-taminated soils by flotation technique. Theseparation of organic material from soil by flota-tion has been used in industry for the separationof bitumen from oil sands [4]. Flotation can alsoremove some metallic contaminants. Thus thisrelatively inexpensive technology has considerablepotential for the remediation of hazardous wastesites.

While it is known that flotation can remove asignificant part of hydrophobic organics from soil,there has been no systematic investigation on suchremoval from soil by flotation. Van Rijt [5] foundthat in contrast to metallic pollutants concen-trated mostly on fine particles, organic contami-nants like polyaromatic hydrocarbon (P AH) arehomogeneously distributed on soil particles. Re-moval of organics by flotation was more effectivefrom coarse fraction of soil [5]. Clifford [6] inves-tigated removal of organic contaminants fromriver sediments by froth flotation. Using a con-ventional flotation unit, 60-800/0 of contaminantswas removed by this method. In a recent patent[7], it was proposed to first separate hydrocarboncontaminated soil by wet sieving into coarse andfine fractions. The coarse fraction is subjected toflotation to remove hydrophobic contaminants.Fines are treated with a hydrocarbon solvent fol-lowed by an aqueous surfactant solution. Wili-chowski and Werther [8] investigated the use offlotation for the washing of mineral oil pollutedsoil. Integration of pneumatic flotation into thesoil-washing process increased purification effi-ciency from 70 to 93%. It should be noted thatmany important parameters such as the concen-trations of collectors and frothers, pH, and kineticcharacteristics were not considered in the aboveworks.

The objective of this study was to test thefeasibility of the flotation process for the removalof non-volatile hydrophobic compounds fromcontaminated soils and to investigate the effect ofbasic parameters such as conditioning and flota-tion time, surfactant dosage, pulp pH, solid/liquidratio in conditioning and pulp temperature. Flota-tion tests were carried out in both a conventionalmechanically agitated machine (Denver cell) and aflotation column.

2.4. Column flotation

Column flotation experiments were carried outin a glass column of 12.5 cm in diameter and 20cm in height, fitted with a fine porous glass frit at

L. ZlIDIIg et aI.jCo/loids and Swfaces A: P/rysicoc'-. EIIg. A.Ipet:l.r 177 ~l) 235-246 237

the bottom. Compressed air was introduced intothe column through the frit. An impeller operatedat 300 rpm was installed for good distribution ofthe air and the soil slurry during the flotation. Forexperiments above ambient temperatures, thecolumn and the air inlet tubes were wrapped withelectrical heating tape to heat both the slurriedsoil and the incoming air and the slurry tempera-ture was monitored. In every run. 20-30 g sam-ples of the contaminated soil were mixed withdesired volume of water and the surfactant orother flotation agents to be tested. and transferredinto the column.

3. Flotation results

3.1. Mechanically agitated cell (Denver cell)

2.5. Soil washing

Soil washing was carried out in the same con-tainer that was used for column flotation butwithout air flow. The impeller speed was increasedto 500 rpm to improve the agitation.

2.6. Stirred media mill

The vertical-stirred machine (built at ColumbiaUniversity) used a four-pin impeller of 10 cm indiameter as agitator. Speed control was obtainedby means of a direct current motor with a rectifierand voltage regulator [9]. No grinding media wasused for soil attrition. A fixed amount of SDSsolution was mixed well with the soil beforemilling. Mter the stirring was completed, the sam-ple was transferred to the flotation cell.

3.1.1. Effect of flotation reag~t typeDifferent types of collectors tested for the flota-

tion of oil contaminated soil include anionic sur-factant SDS, cationic surfactant DT AB, andnon-ionic surfactant pentaethoxylated nonyl phe-nol (NP-5). Pine oil was used as the frother. Theexperimental conditions and the results obtainedare summarized in Table I. In the table thereagent concentrations are in reference to thesolid, i.e. mg of reagent per kg of solid. The oilcontent is normalized using the extraction effi-ciency. Oil distribution in the floats (sinks) iscalculated as:

oil amount in float (sink)/total oil amount

A maximum recovery of 400/0 was obtainedwith a combination of SDS and pine oil. Cationic~nd non-ionic surfactants were not as good as theanionic surfactant as collector. Another advan-tage of the anionic surfactant was its low sorptionon soil particles, which are mostly negativelycharged. For further tests SOS was chosen as thecollector.

2.7. Oil analysis 3.1.2. Effect of conditioning timeConditioning time used in the preliminary tests

was 3 min. Since generally an increase in condi-tioning time can enhance interactiQn betweensolids and surfactants and benefit the flotationprocess, the effect of conditioning time was deter-mined. It can be seen from Fig. I that increase inconditioning time from 3 to 15 min caused ameasurable increase in oil removal. A condition-ing time of 30 min was chosen for further tests.

The concentration of paraffin oil in the soil wasmeasured gravimetrically. Oil was extracted fromthe soil by mixing a fixed weight of the soil with200 ml of hexane for 30 min. The slurry wasfiltered and the filter cake washed by hexanerepeatedly to remove all the dissolved oil from thesoil. The hexane was evaporated from the solutionuntil the weight remained constant. The oilamount was determined from the difference inweight of the residue. The extraction efficiencywas obtained from results of the experiments withartificially contaminated soils.

3. J .3. Effect of flotation timeIn order to determine the effect of flotation

time, floats were collected at different times and

238 L ZiIaIIg ~I a/. /Colloldr and SlU/tICe.f .4.: Physicochem. Eng. Aspects 177 ~/) 235-246

analyzed separately. The total flotation time forthis test was 30 min. The results obtained aregiven in Table 2 and the cumulative oil amount inthe floats is plotted in Fig. 2 as a function offlotation time. As expected, the oil removal in-creased with flotation time. However, floats col-lected during different time periods had almost

the same oil content. This is unusual since nor-mally the content of hydrophobic particles de-creases with flotation time in ore flotation. Therewas not much soil collected after 5 min of flota-tion, and the collected floats were mostly clayparticles entrapped in the bubbles. Based on theresults obtained it can be seen that in these flota-

Table IEff«:t of reagent type on flotation of oil-

Oil distribution(O/.)b

Oil content~/.)

Removal efficiency byflotation <-lor

5.2920.8089

5.336

~.677.3

33.9

22.7

40.0

Sink

Float

117 93.7

3.1$

0.6412

5.639

S).O

17.7DT AD 100 miJkg + pineoil 20 mg/kg

6.27 21.8

Sink

Float

193

2.4

96.1

1:2IJ

0.8105

5.657

78.2

6.8NP-5 100 m&'k:g+pine oil20 mg/kg

7.1

Sink 197 98.8 0.9426 92.1-. Experimental conditions: conditioning time with collector: 3 miD; flotation time: 5 min. Pulp pH 6.5.

b The sum of oil distribution in ftoat and sink may be less than 100'/. since some oil goes to the solution in the flotation process.C Removal efficiency by flotation = 1 = oil distribution in the sink.

so

45

~1J"6

40

3S

300 , 10 IS 20

Conditioning Time, minute

2S 30

Fig. I. Oil removal as a function of conditioning time

239L. Zhang el aI. / Colloids and surfaces.4.: Physicoc/rem. Eng. Aspects 177 (.2001) 235-246

Flotation Time, minute

Fig. 2. Effect of flotation time on the oil removal.

tion tests the oil removal may be partly due to theentrapment of contaminated fine particles in thefroth, as contaminants such as metals and organicsare known to become concentrated in the finefraction of the soil. While entrainment is consideredto be undesirable in mineral processing operations,in this case this effect may be advantageous sinceit can remove the clay-bound contaminants.

Although the oil removal increased with flotationtime, very long flotation time may not be practical.This can be resolved by intensification of theprocess, by, for example, increase of the reagentdosages and use of multistage flotation.

3.1.4. Effect of the collector dosageThe effect of collector (SDS) dosage was tested

with 10 min of flotation time. It can be seen thatas collector dosage increased efficiency of oil re-moval as well as the yield of floated particlesincreased (Fig. 3). The effectiveness of separationdepends on both these parameters. In order to geta quantitative estimate in terms of both, a coeffi-cient of separation (E) was calculated by subtract-ing the weight percent of the float from the per<;entof total oil removed by flotation:

E = (% oil removal) - (% weight distribution)

L. Zhang et aI.! Colloids and Surfaces A: Physicochem. Eng. Aspects 177 (2001) 235-246240

In the present study, the coefficient of separa-tion obtained for flotation with 200 mgjkg SDSwas close to that obtained with 300 mgjkg dosage.Since for environmental purposes, the oil removalis usually more important than the yield. 300mg/kg SDS was chosen as the collector dosage forfurther tests.

liquid ratios (1:3, 1:2) was carried out in a sepa-rate cell. After conditioning, the pulp wastransferred to the flotation cell and diluted to thedesired 1:5 ratio for flotation.

Results obtained at different solid/liquid ratiosduring conditioning are shown in Table 3. It canbe seen that with increase in solid/liquid ratio theoil removal decreased.

3.1.6. Effect of stirred media millStirred media mill was considered with the aim

of removing surface contaminants for froth flota-tion [10]. Since the contaminated oil is usuallycoated on the surface of the soil particles or

3.1.5. Effect of the solid/liquid ratio inconditioning

The solid/liquid ratio in the conditioning stagewas varied to test its effect on subsequent flota-tion processes. However, in order to keep otherparameters constant, conditioning at high solidi

~

I~

~10

~~

"<5

Fig. 3. Oil removal and yield of floated soil as function of SDS dosage.

3'1;$IS.884.2

22.877.2

14.086

3.5020.5040

2.2580.5426

2.8940.5272

55.042.2

51.241.7

40.245.1

l:S FloatSink.

FloatSink.

FloatSink.

sa.31:3

s.c":2

31.4167.5

45.31.53.8

27.8171.1

L. Zhang et aI. / Colloids and Surfaces A: Physicodlem. £IIg. Aspects 177 (2001) 235-246 ~t

~

f~tIJ

-a>0!-"<5

Fig. 4. Effect or rotation speed or stirred media mill on oil removal.

3.1.7. Effect of pulp pHThe interactions between the collector and the

soil can be affected by the pulp pH. Flotation wasconducted using 300 mg/kg SDS as collector atnatural pH (6.5) and elevated pH (9, II). Theresults showed the oil removal to vary less than1 % at different pH and suggested the pulp pH tohave small effects on the oil removal. In subse-quent tests pulp pH was not adjusted.

3.1.8. Effect of two-stage flotationIn industrial practice flotation is a continuous

multistage process and flotation reagents are con-tinuously added. Two-stage flotation tests weretherefore carried out in an attempt to simulateindustrial conditions. The collector dosage andtotal flotation time were kept the same as those ofone-stage flotation in order to facilitate compari-son. With stirred media mill, the two-stage flota-tion increased the oil removal to 74%, 5% higherthan that obtained with one-stage flotation.(Table 4).

placed in the outer layer of the grains, it should bepossible to remove the oil from the grain surfaceby means of attrition. The liberation of a contam-inated material mixture into its components is thebasic and the first step to efficiently reduce the soilcontaminants to a degree, which permits the reuseof soil at its original location.

In the stirred media mill, the attrition powerdepends, among other things, on the rotationspeed and the effect of stirred media mill on theflotation process was therefore tested at differentrotation speeds. Towards this purpose, 200 g ofsoil samples were mixed with SDS solution in thestirred media mill for 30 min at a solid concentra-tion of 700/0. Mter stirring, the samples weretransferred to the flotation cell and diluted tolower the soilfliquid ratio to 1:5.

The results show the oil removal to increasewith the rotation speed of the stirred media mill(Fig. 4) due to enhanced attrition of soil particles.The supernatant becomes more cloudy, suggestingthat many fine particles/oil droplets have beencreated by the strong attrition. At the samereagent concentrations (SDS 300 ppm, pine oil 20ppm) and experiment conditions, a 10% increaseof oil removal was achieved using pretreatmentwith the stirred media mill at 1500 rpm.

3.2. Flotation column

Two approaches were explored in column flota-tion. One approach involved oil removal by flota-

j

L. Zhang et aI.1 Co/Joidr and Surfaces .4: Physicochem. Eng. Aspects 177 (200.1) 235-246242

tion with anionic and non-ionic surfactants atconcentrations well below the critical micelle con-centration (CMC). The other involved flotationwith an alkaline solution (pH 10) at elevatedtemperatures.

temperature and solid/liquid ratio were testedwith the coarse soil fraction (250-800 Jim) con-taining 1% oil by weight. The results obtained aregiven in Table 5. Triton X-IOO and SDS havesimilar effects at the room temperature. Increasein temperature was found to improve the removalefficiency, especially when Triton X-tOO was usedas the collector.

The effect of the soil-to-water ratio on flotationwas also explored (Table 5). Flotation was carriedout using 30 g raw sample of soil in 120 and 200ml of solutions. Little difference was observedbetween the two test results.

Kinetics of oil removal using 50 ppm SDS isillustrated in Fig. 5. Based on these experiments, aflotation time of 30 min was chosen for furtherwork. Oil removal by flotation for 30 min in-creased from 61 to 67% when a high SDS concen-tration of 200 ppm was used. However, more finesoil was picked up in the foam. Increase in the pH

3.2.1. Flotation using surfactantsAnionic SOS and non-ionic Triton X-IOO at

concentrations of SO ppm in the solution (or 333mg per kg of soil) and pine oil at 20 ppm (133 mgkg-I) were evaluated for oil removal. Resultsobtained were similar for both surfactants. It wasfound that pine oil did not improve the oil re-moval significantly, however it did cause more soilto float and become trapped in the foam at thetop and hence the use of pine oil was discontinuedin further experiments.

To determine optimal conditions for columnflotation, a series of tests were carried out as afunction of relevant parameters. Effect of pulp

Table 4Results of two-stage flotation.

4.2391.2360.3407

3.7641.2750.3494

4.0411.4790.3356

S9.67.8

2S.9

SS.S8.7

26.9

54.69.0

25.7

74.1Float IFloat 2Sink

Float IFloat 2Sink

Float IFloat 2Sink

21.112.6

1.s2.2

29.S13.6

154.2

2712.2

153.2

14.576.53

78.9

14.956.89

78.16

14.037.34

79.63

73.2

74.3

. Experimental conditions: conditioning time: 30 min; SDS (first stage): 200 mg/kg; pine oil (first stage): 20 mg/kg; flotation time(first stage); 5 min; SDS (second stage): 100 mg/kg; pine oil (second stage): 10 mg/kg; flotation time (second stage): 5 min.

JRemoval efficiency (0/0)

Table 5Removal efficiency of oil from son by ftotation at different temperatures and solidj1iquid ratios

--

Soil{liquid ratio (g/ml)Surfactant SO ppmTemperature

626473797078

30/20030/20030/20030/20030/12030/120

222245454545

SOSTriton X-IOOSOSTriton X-IOOSOSTriton X-IOO

Zhang et oJ.! Colloids and Surfaces .4.: Physicochem. Eng. Aspects 177 (:6XJ1) 235-246 2A3

~J

Fig. 5. The kinetics of oil removal with SDS.

of the slurry to 10.5 had little effect on the oilremoval using flotation with SDS as collector.

3.2.2. Flotation using alkaline solutionFlotation with hot alkaline solutions is used in

industry for the separation of petroleum frombitumen sands. Usually temperatures near 80°Care used for this purpose. According to the litera-ture [4,11], a pH value of 10 is optimum for thisseparation, as more basic solutions form undesir-able stable oil-in-water emulsions. At high pHvalues both oil and sand minerals, such as silicaare negatively charged and are dispersed bycharge repulsion. To our knowledge, this work isthe first attempt to test this technology for theremediation of contaminated soils.

In initial tests, the pH was raised to 10 usingNaOH before air flow was commenced. However,the pH generally dropped to about 8.5 by the endof the experiment, due to lack of buffering.NaOH was replaced by Na2CO3 in later experi-ments. The carbonate buffered the solution moreefficiently, and the pH was 9.2 after 30 min offlotation. Unless stated otherwise, experimentswere carried out with 250-830 ~ fraction of thesoil.

Flotation experiments were carried out with250-830 lA-m fraction of the soil. Kinetics of oilremoval using flotation with Na2CO3 solution atsoil/water ratio of 30 g/200 ml and temperature22°C is illustrated in Fig. 6. Based on these resultsa flotation time of 30 min was chosen for furtherwork. It was found that, for flotation in alkalinemedium, oil removal efficiency improved uponincreasing the temperature (Fig. 7). When thetemperature was increased to 45°C, removal rateswere 83 and 78% at soil/liquid ratios of 30 g/120ml and 30 g/200 ml, respectively. Oil exhibitsadhesive behavior at lower temperatures, and as aresult, remains attached to sand particles oncethey are entrapped. When the oil viscosity isreduced by increasing the temperature, oil de-taches more readily from particles by stirring. Thenegative zeta potential of silica increases withtemperature [4], enhancing repulsion between oiland sand particles.

The oil removal was found to be more efficientwhen a higher solid/liquid ratio was used for thesame amount of soil (Fig. 7). This may be due tothe higher density of dispersed air in the slurry, orto the increased contact between the particles in

L. Zhang et aI.! Colloids and Surfaces A: Physicochem. Eng. Aspects 177 (2001) 235-246244

the slurry as a result of collision/attrition. Addi-tional experiments on the effect of soil-to-liquidratio and the total volume of slurry floated ineach experiment were undertaken in an attempt toclarify this point. It was concluded that thereexists an optimal solid/liquid ratio for oil removal

(Table 6). At low SjL ratios the reagents arediluted, while at very high SjL ratios there may bepoor mixing and separation.

Alkaline hot solutions were also used for flota-tion of soil containing particles of a wider range(75-830 ~). As expected, the efficiency obtained

j

~

~'uISu

Fig. 6. The kinetics of oil removal with Na2CO] solution (pH 10).

T~,OC

Fig. 7. Removal of oil from soil using flotation with alkali solutions.

245L. Zhang et ai. / Colloids and Surfaces .4.: Physicochem. Eng. Aspects 177 (2001) 235-246

Table 6Effect of changes in soil and liquid ratios on eff~tiveness of flotation at pH 10 and 22°C

3012072

30300S8

2020061

3020068

5020063

Soil mass (g)Liquid volume (mI)Removal efficiency (%)

Table 7Removal efficiency of oil from soil by washing with surfactant

4858456264

SDSSDSTriton X-tOOSDSSDS

2222224545

so5000

SOSO

5000

30/20030/20030/20030/12030/120

Eighty to 900/0 removal of such contaminants as-PCBs and PAHs from soil have been reported inthe past using 0.5-2% surfactant solutions [12].The low efficiency in this case may be due to thesmall size of the particles in the soil sample used.The limited solubility of the highly hydrophobicparaffin oil used in these experiments may alsoaffect the soil washing process.

was lower (66%) than that obtained for the 250-830 ~ fraction (83%). When alkaline flotationwas used for the coarse fraction (250-830 ~),almost no soil particles were levitated by thebubbles in contrast to about 3% for the 75-830Jim soil. Foaming and floating of finer particleswere substantially less in the alkaline flotationthan when surfactants were used.

3.3. Soil washing4. Conclusions

The feasibility of paraffin oil removal fromartificially contaminated soil by flotation usingconventional mechanically agitated machine(Denver cell) and flotation column has beendemonstrated. Effects of reagent type, condition-ing time, flotation time, surfactants dosage, pulppH, pulp temperature and solidfliquid ratio inconditioning were determined.

With Denver cell, a 74% oil removal can beachieved for the 75-830 ~ soil fraction by theuse of stirred media mill and two stage flotation,using SDS as collector and pine oil as frother.With the flotation column, up to 800/0 of the oilcould be removed from the 250-830-~m soil frac-tion using either surfactants (SDS or Triton X-100) or sodium carbonate at pH 10 and 45°C.With the 75-830 ~m fraction, removal efficiencieswas about 65%. It is expected that the efficiencyof oil removal will be higher for the coarse soil

To compare the oil removal efficiency with soilflotation, soil washing was carried out using thesame sample in the same cell with the impeller,but without an air flow through the porous frit.To improve the agitation, the impeller speed wasincreased to 500 rpm. The oil removal efficiencyobtained after 30 min of washing using surfactantsolutions is presented in Table 7. The efficiency ofthe soil washing process is less than that obtainedwith flotation under the same experimental condi-tions (Table 5), even at the higher surfactantdosages.

Soil washing was carried out also with asodium carbonate solution at pH 10 and 45°C.The removal of oil by washing using hot alkalisolution is 76%, higher than that using SDS atnormal or elevated temperatures, but less thanthat by flotation with the same reagent under thesame conditions.

L. ZioIIg et aI. / Co/low and Surfaces A: Physicochem. Eng. Aspecl.f 177 (.200/> 235-246246

fraction. These results indicate that the flotationprocess can be successfully applied to reduce sub-stantially the amount of non-volatile hydrophobiccontaminants in the soils.

It is shown that for the same soil, oil removalby flotation is more efficient than that by soilwashing. Other advantages of flotation over soilwashing include lower surfactant dosage and re-duced emulsion formation. It is clear that flota-tion has considerable potential for cleaningcontaminated soils. ~

Acknowledgements

The authors are grateful for the support of theUSEP A Northeast Hazardous Management Re-search Center and the National Science Founda-tion crs-9622781.

[2) W.C. Anderson (Ed.), Innovative Site Remediation Tech-nology: Soil Washing/Soil Flushing, American Academyof Environmental Engineers, Annapolis, MD, 1993.

[3) J.L. Underwood, Soil cleanup by in-situ surfactant flush-ing. Ill. Reclamation of multicomponent sodium dodecyi-sulfate solutions in surfactant flushing, Separation sa.Technol. 30 (1995) 2277-2300.

[4) Q. Dai, K.H. Chung, Bitumen-sand interaction in oilsand processing, Fuel 74 (12) (1995) 1858-1864.

[5) C. van Rijt, Cleaning contaminated sediments by separa-tion on the basis of particle size, Water Sci. Technol. 28(1993) 283-295.

[6) S.R. Clifford, Removal of organic contamination fromBuffalo River sediment by froth flotation, Miner. Metall.Processing 294 (1993) 195-199.

[7) R. Varadaraj, Decontamination of hydrocarbon contain-ing substrates. US Patent #5,417,864 (Cl. 210-703),1995.

[8] M. Wilichowski, J. Werther, Applicability of flotation inthe washing of soil, Chem.-lng.- Tech. 67 (1995) 760-763.

[9) J. Zheng, C.C. Harris, P. Somasundaran, A study ofgrinding and energy input in stirred media mills, PowderTechnoL 86 (1996) 171-178.

[10] J.E. Norman, O.C. Ralston, Conditioning surface forfroth flotation. AIME Technical Publication, 1074, 16,1939.

[II] Q. Dai, K.H. Chung, Hot water extraction process mech-anism using model oil sand, Fuel 75 (1996) 220-226.

[12] D.A. Sabatini, R.C. Knox, J.H. Harwell (Eds.), Surfac-tant-Enhanced Subsurface Remediation: Emerging Tech-nologies, ACS Symp. Ser., 594, 1995.

References

(1] R.A. Griffiths, Soil-washing technology and practice, J.Hazardous Materials 40 (1995) 175-189.

.~4