CA2089639A1 - Surfactant selection method for the extraction of chemical pollutants from soils - Google Patents

Abstract

SURFACTANT SELECTION METHOD FOR THE
EXTRACTION OF CHEMICAL POLLUTANTS FROM SOILS

ABSTRACT OF THE DISCLOSURE

The physics of adhesion are applied to choosing sur-factants that have Lewis acid-base and dispersion force in-teraction values which are required to optimally extract pollutants (10) from soils (12). This application is novel in predicting a surfactant's effectiveness in the removal of toxic contaminants. Additionally, Lewis acid-base and dispersion forces are applied to the selection of a co-sur-factant to improve the adhesion between a surfactant and a pollutant.

Description

6 3 ~
PATENT

SURFACT~NT SELECTION METHOD FOR TH~
EXTRACTION OF CHEMICAL POLLUTANTS FROM ~OILS

~S~C~Q~LÇE~ IN~E~TIOM
1. Fi~d ~f th~ InYQntiQn The pre~ent invention i~ direct~d to ~h~ oxtr~ction o~
cha~ical pollutan~ grom ~he ~oil, snd, Dor~ particularly~
~o the s~lection of 8pec~ic ~ur~act~nt~ to ~xtract Specir ic pollutants from a given ~o$1.

2~_~escri~tiQn ~f R~lated Ar~
The clean-up o~ all the hazardous waste sites in A~er ica is an enor~ous task. Not only i~ the number of ~ites growin~ each year, but also the clean-up of ~he sites is di~ficult bo~h technologic lly and econo~ically. The num-b~r of CERCLA (Comprehensive knvironmental Resource Conser-vation Liability Act) Super~und sites on ~he National Pri-ority List is large ~1,236 ~t the pres~nt ti~e) ~nd gro~ing each day. Increasing legal re6trictions on ~l~an-up prac-tices ~ake it even more diff~cult to co~ply ~ith respon~
bilities. Landfills no longer accept h~z~rdous wa~tes.
Soil aeration i~ prohibited in most populated reyion~.
Pump and treat methods have been ineff~ctive in ~any cases.
Rules against burying and discarding waste~ have prolifer ated. Treatment plans and schedules ~ust be submitted to the EPA, the local agencies, and to the public for approv-al, which can impose more constraints on remediation choic-es .
In res~)onse to increased environmental concern, numer-ous innovative clean-up technologies have been proposed by both public agencies and private companies. Table I below 2 2~8963~
shows extruction and destruction techni.ques which have been proposed ~or polychlorinated biphenyls ~PC~ xtrsction and de6truction o~ toxic chemic~l~ ure accomplished ~hrough chemical, thermal, or machanic:~l mean~,. A C08t e~ective combin~tion of both extraction ~nd destruction i8 desired.
Effectivene~s and cost con~idsrations are hi~h on the list of priorities, so any proposed clean-up approach ~ust be more effective and cos~ lass th~n existing technologies.

Table I. Treat~ent ~ethods.

Solven~ ~lectron ~e~a Steam heating Solvent de~hlorln~tion Surfactants Biore~ed~ation Supercritical fluids Incineration Pu~p & treat _==--=__=== --_____==__======_ The difficulty in cleaning contaminated scils today is that, depending on the conta~inant, acceptable contamina tion limits are irl the range of parts per ~illion or less~
Most of the technologies currently used in soil remed~ation are either not capable o~ meetin~ thesa standards or are not ~ea6ible for economic reasons.
Very high concentration sludges ~ay bs eff~ctively decontaminated by tharmal destruction technigues such a~
incineration, or plasma torch, or electron beam irradia-tion. ~ut low level conta~ination spread out over hundredsof thousands o~ cubic yards of soil re~uire~ other, less costly methods. Here, chemical or biological tr~atment technologies would take longer, but would cost orders of magnitude less than incineration. Although bioremediation 3~ is difficult to engineer, both bioremediation and soil washing impose the least harm to the environment. Thes~
latter techniques are also potentially the least costly.

2~38~3~

Current t~chnology can be used to enhsnce the~e techniqu~s so they carl reduce conta~ination to the regul~te~ levels.
Like all remediation techniques, sur~act~nt trentment al ~o has l ts advantages and d:isadvantage~ 0 It i8 :Lnexp~n-6iV8, non-toxic, and re~oveæ ~Ind concentrs.te~ pollutants before destruction. However-, although extract~on take~
place; there is no destruction o~ the contarainant, ~e extracti~n process can be slow, and removal o~ l~rg~
contaminant concentrationæ can be lmpeded unless l~rge scale earthr~oving, grindin~ nd mixing operation~ ~!are pex-formed. Many experiments rely on 80111bility to pred~ t per~orma~ e, only to $ind that upon appllcatiorl to ~ r~l s1te, solubillz~tion og pollutg~nts v~rie~ tical~3Ly ~
soil condition~ Thu~, ~o~0 sur~ctant~ ~re not a~ eS~eo-tive in the field as expect~d ~ased on lab an~lysi~. Other proble~s which emerge in field tests are enou~h to stop pursuits with this technologyO
The distribution o~ conta~inants in ~oil~ depends upon the porosity o~ the soil and thQ ~ctual ~iner~l content of the soilO Conta~inants adhere to soil con~tituents wi~h varying strengths. Presently av~ilable are a variety o practical and empirically-derived tools which providQ yard-stick measurements to surfactant per~ormahce. So~e o~
these tools include hydrophilic-lipophillc balance (HLE~
values, solubility resul~s, previous experi~ent~l r~sults, etc. The proble~ with the~e tools i~ th~t ~hey ~11 requir~
nu~erous exper~mental test~ o~ a var~sty o~ sur~actant~, most of which ~re che~ic~l formulation~ b~ unknown (to the user) compounds. The use of physical model6 helps to pro-vide a more realistic and quan~ifi~ble understanding o~
~urfactant action. A coherent evaluation of the che~istry and physics of adhesion can reduce, if not eliminate, poor surfactant selections.
Thus, a need remains for a predictable method of de-tarminin~ the appropriate approach to removing contaminants in the soil using surfactants.

4 2~8~3~
~g~ "~ ON

In accordance with the invention, ~ me~hod is proYided for sslecting the appropriate surfsctant, or 3ur~ct3nts, 5 . for the removal of a givan contaminant ~rom a 5peci~ic soil. There are three aspec:ts to surfactant selection:
characterizatlon of the soil, contact angl~ ~easure~ents to determine the sur~ace energiel3 of pollutant~ on soil8, and estimation o~ the chamical nature ~f the sur~actant ~hich 1~ would provide effective removal.
Application of ths method of the inventisn ch~racter-izes the po~ar and non-~lar contribution~ o~ th~ s~r~e-t~nts needed to extract the partleular conta~in~nt ~ro~ ~h~
80i 1 . Th~ s~ruc~ure o~ th~ surfactant i~ dictated ~ro~
these polar and non-polar forces. SeleGtion o~ surf~ctants can be predicted from the actual chemistry of the soil-pol-lutant syste~, thus reducing time and effort spent on nu-m~rous exparimental trials.

20BRIEF aE~ç~IpTIoN QF TH~ ~R~WI~G~

FIG. 1 is a ~che~atic diagra~ depicting the 801ubility and ~ormation of micelles;
FIG. 2 is a cross-sectional view, depicting a drop Or liquid on ~ solid surface, and showing the ~ontact angle;
and FIGS. 3a and 3b ~re sche~atic diagraffls depicting khe signific~nce of cont~ct angles ~n oil remoYal.

~

Solubilization of contaminants is a multi-stage physi-cal process. FIG. 1 schematically depicts the roll~back mechanism for removal of oil 10 which is adhered to rock 3512. l~he oil 10 is surrounded by surfactant ~olecules 14 oriented so that the lipophilic end 14a lines up towards the oil 10, while the hydrophi~ic end 14b is surrounded by 2a~3~

water (which surround~ the as~e~bly shown in FIG. 1, but which is not dapicted). The sur~actant 14 acts to lniti~te drop formation, ~ollowed by necking and eventual oil remov-al and the ~ormation of micelles.
The pre~ent invention i5 directad to the lniti~l re-lease rather than the formati.on o~ ~icelles in ~olution.
In particular, the present invention is directed to the selection o~ one or more appropriate sur~actants to remove contaminant(~) ~ro~ a glven soll.
1~ There are three aspacts to sur~actant ~elect~on: char-acterization of the soil, contact angle mea6ure~Qnt~ to de-tarmine the ~rface en~rgies of pollutant6 on 8011~, and estimation of the che~ical natur~ oP the s~r~act~nt ~hlch would provide effective r~oval.
Specifically, a full characterization o~ the conta~i-nated site soil mineralogy is required. Then, measure~ents o~ the contact angle between the contaminants o~ interest and three types of surfaces are necessary. These measure-ments provide the surface tension contr1butior.s to the in-teraction energy between the contaminant and the soil. To determine the adhesive force between sur~actants and con-taminant, interfacial ensrgy measurements between sur~ac-tant (polar and non-polar groups) and test sur~aces ~ust be made. The test surfaces may be the sa~e as ~hose for de-tsr~ining the interaction energy bet~e¢n the contaminant ~nd the soil or they ~ay be different. ~h~ important a pect is-to obtain well-defin¢d valus~.
Intarfacial tension betwe~n surfactants and the soil can be computed to assist in evaluating whether selected surfaotants may adhere to soils. Surfactant non-polar and polar ~urface tension contributions (based on surfactant chemical structures) are evaluated in terms of the total free energy of interaction between the contaminant and sur-factant versus contaminant and soil to predict the perfor-mance of existing and novel surfactant molecules.
Application of the method of the invention will char acterize the polar and non-polar contributions of the sur-2 ~ 3 ~

fact~nts need~d to e.xtract the p~rticul~r conta~in~nt ~rom the soil. The structure o~ the 6urfactant will be dlctat~d from these polar and non-polar ~orce~. Sel~ctlon o~ ~ur~
factants can be prsdicted ~roDI the actual chemi~try o~ th~
soil-pollutant system, thus reducing ti~e ~nd e~ort spent on numerous experi~ent~l tri~
Intaract1ons o~ sur~actants ~it~ clay~, 6illcn, and other ~oil minerals can ks predicted fro~ the teaching~ o~
this invention.
The surfactant sel~cti4n ~ethodology i~ de~cribed be-low. It includes contributiorls ~ro~ surfac~ che~i~try and appli~s ~h~m ~o sur~actant per~ormance for ~he re~edi~tion of ~oil~. The ~et~od o~ ~be in~ention pro~ids~ ~or bo~h ~he d~termination o~ th~ su~f~e ~dhesiv~ ~orce~ het~een 1~ the contaminant of interest and ~he 80il8 in ~hich the con-taminant(s) lie, and the determination of the surface adhe-sive forces between the sur~actant and conta~inant and be-tween the surfactant and soils.
Having selected the surfactant (or combination of sur~actants) based on the teachings herein, any of the well-known in ai~ and on-site reactor 50il remediation processes and apparatus may be employed to treat the conta~inated soil. These extraction proce~ses and appara-tu~ are well-known and do not ~or~ a part of this inven-tion, which is direct~d to the selection ~P th~ Gur~ac~tant(s~ ussd to treat the conta~inat~d 80il.

I~ SQil Cbn~çt~riZatiQn.
The ~irst step is to determine the mineral charact~r of the soil. ~ineralogy is needed to deter~ine the a~he-sive energy between the soil and the pollutant. The adhe-sive energy is the force which must ba overcome by the sur factant to remove the contaminant.
The principal tool for this work, X-ray diffraction, can be found in typical mineralogy laboratories. Typical-ly, minerals are identified, together with how their com~
position varies with particle size. For example, there are 3 ~

coarse, medium, and ~ine grained 8ilic~8; however, in soils, clays are typically ~iner grained th~n sili~as.
For example, a Siemens D-500 ~i~fracto~atar, driven by a DEC Microvax computer and equipped wlth a copper anode X-ray tube operating at 40 XV and 30 mA, is suitably e~ployedin soil analysis. A graphite diffracted~be~ ~onochro~ator is positioned betwaen the sample and the detec or. Analy-sis is done grinding the soi:L sample to pas~ ~ 350 ~e~
screen and then recording tbe diffraction pattern. The patterns are identi~ied through a JCPDS (Joint Co~ittee on Powder Diffraction Standards) Powder Digfracticn File stored on computer. Search is both ~uto~ati~ using Siam~n~
so~tware and manu~l by visual inspsction. ~ch ¢on~tltuent minernl phase present in quantities grea~er th~n 5~ by vol-ume c~n be identified.
A sample from a PCB-conta~inated site was taken and dispersed in distilled water. Two ~ractions of snil were taken based on particle size which were, roug~ly, the clay (fine) fraction and the coarser fractionO Th~ fine ~rac-tion was deposited on a glass slide using a ~onventionaltechnique for clay ~ineral analysis. The coarse fraction was packed in a bulk sample container. The diffract~on pat~erns for both were similar, indicating that both con-tain essentially the sam~ minerals, but not necessarily in the same proportions.
The do~inant mineral was guartz, with ~inor a~ount~ o~
other silicates. This ~ineralogy, li~ted in Tabl~ II, is typical o~ a soil derived from glacial sedi~ents and reflects the igneous rock types in Canada, ~he source of these sediments.

Table II. Mineral Analysis.

Mineral Relative Abundan~e ~inç~dl-Iy~
Quartz major tektosilicate Chlorite minor clay ~ineral 208~39 Illlte minor cl~y ~lneral Orthoclase minor tekto~ cate Enstatite minor ino~ilic~t~

II. De~ermin~lon Q~ ~n~ L~bce4c~ by~l9~.
Determining the inter~acial polar and non-polar inter-actions b~tween solids and liquids is known; ~e, e.g., C.J. Van Oss et al, "Inter~aci~l Li~shitz - van der Waals and Polar Interactions in ~croscopic Syst~ , Çh5~
~e~iews, Vol. 88, No. 6, pp. 5127-941 (198~). Furt~er, ~-t~rmin~ng the acid ba~s inter~ctionR bet~2en clay ~i~r~l~
and hu~an se~u~ albu~in in aqueous ~dla throug~ a ~erieR
of contact angle measura~ents is ~lso known; 8ee , ~ . g ., P.M. Costanzo et al, "Determination of the acid-bas~ char-acteristics o~ clay min2ral surfaces by contact angle ~ea-surements", Vol. 4, No. 4, pp. 267-275 (1930).
The inventors have discovered that the foregoing pro-cedures can be applied to the treatment of contaminated soil with surfactants.

A. ~Qnta~Anqle ~asuremen~.
Young's e~uation, which defines the surface t~nsion (y~.~ be~ween a ~olid (S) and liguid ~L), c~n be co~puted from measuring th~ contact angle (~IG. 2), given ~he sur-face tension between the solid and air (~,~) and the liquid and air (y~):

Y~.~ ~ YS,~c~s~ ( 1 ) FIG. 2 shows the contact angle ~ which a drop 20 of liquid ~akes with a surface 22.
Contact angle provides a measure of wettability. As shown in FIG. 3a, in a water-oil-silîca syste~ (the water is not sho~m in the drawing, but surrounds the assembly), 2~9~39 oil 10 does not spread on ~wet) the sub~tr~t~ 12, but will form A finite contact an~le in water. FIG~ 3b shows that the sur~actant solution (agai,n, not ~hown) in place o~ wa~
ter reduces the sur~aCQ tenfiion between the substr~t~ 12 and the oil 10, snough to pull the oil into ~olution. Dur-ing soil washing, ~e surfactnnt bath ~ill spontaneously displace the oil from the sub~strate when tha contact angl~
is 180'; i~ th~ contact ~ngle~ ~s less than 180 but ~ore than 90-, the contaminant wll.l not be dlsplaced spontan~-ously but might ~ removed by hydraulic curr~nts in thebath. When the contact angll_ i8 les~ than 90 , ~t least part o~ the contaminant ~ill rem~in att~ch~d to the 8Ubo strate. ~n oil-wat~r syste~, hydrogen ~ondi~g pl~y~ ~
signi~icant role in ~he oil-water sur~aoe ten810n ~nd ~he interaction with the substrate, thu~ the 6ep~ration o~ po-lar and non-polar contribukion~ is needed.
In order to calculata the free energy o~ adhesion o~
the contaminant with the solid substrate (or soil), one must obtain independent surface tension values wh~ch are divided into non-polar (Li~sh1tz-van der Waals: L~) and poo lar (Lewis acid-base: AB) surface tension values. A total of three values are determin2d f or each conta~inant ~nd soil mineral type. One of the three values i8 bns~d upon the non-polar dispersion ~orces o~ interaction de~ined by Lifshitz-van der Waals theory and the o~her ~o ~alues ar~
based upon two polar forces of ~nteract~on defin~d by the el~ctron donor and electron acceptor d~inition~ o~ Le~l6 acid-base theory.
The total surface tension of a given material is the sum of its polar and non-polar components:
y = y w ~ y~ 2) where, y w = Lifshitz-van der Waals contribution y~ = 21y'y~)~ = Lewis acid-base contribution y' - Lewis acid surface tension contribution (electron acceptor) 2 ~ 3 ~

y~ 3 Lawis base sur~ace ten~ion contribution (electron donor).

Experimantalists use t~1:al sur~ace ten~ion as one of their yardst~cks in predicting solubiliz~tion. Addition~l valuable in~or~ation can be obtained ~rom th~ division of surface tension into its thr~s chemically ~ign~lcant co~-ponenks, Li~shitz-van der Waals and the positive and n~ga-tive Lewis acid-base components. The thr~e sep~ra~e ener gies are rela~d in the following eguatlon ~or int~rfacial tension between two substanc~ (Y~a) ~ (y ~w~bl~ ~ 2t(~ y3 ~
( Y a 't ~ 3 ~ ~ ( Y l. Y ;t ) ~ ( 3 ) The signi~icance of this equation is ths ~cid-basa in-teraction para~eters. Not only are the acid basc interac-tions between different molecules given, but al80 the acid-base interaction with itself.
The total surface tension of liquids can ~e ~easured or found in published tables. If measur~d, three different surfaces are employed, such as a polytetr~luoroethylen~
~aterial for the non-polar component and poly~ethyl~e~ha~-rylate for the polar (Lewi~ base) co~ponant~. Th~re ar~ no reliable solid surfaces with a larg~ polar (Lewi~ acid) componant. Thus, the L wi~ acid co~ponent o~ the li~uid must b~ computed fro~ measure~ents on anoth~r sur~ac~ with a different Le~is base value, such as poly~tyren~.
The desired surfaces ~ill be in either ~ ~olid, s~ooth crystal form or prepared in a press~d cake with a s~ooth surface which can be reliably reproduced. All surfaces must have known y w, yl~ and y~ values.
Once the total sur~ace tension is known, the y~T ~ can be found by one of t~o methods. One ~ethod is that of Li~-shitz as describ0d by ~.B. Hough et al, "The Calculation of Hamaker Constants from Lifshitz Theory with Applications to Wetting Theory~, ~dvan~es in Colloid and In~rf~e ~ienÇ~, .~D.~
ll Vol. 14, pp. 3-41 (1980)~ where t~e cllspersion ~orces ba-tween bulk materi~ls is ~ouncl ~rom the dielectric o~ the materi~l~ ln question,, the re~ractiYe lndex, etc.
Another method is by measuring contact ~ngles o~ th~
~partly polar) liquid on a ~o~id non-pol~r sub~trate, ~uch as polytetraflucroQthylene or other ~luoroethylene polym~r, knowing t~e value of y,~ and u6ing th~ ~qu~tion:

y",~l + cosO = 2(r~ y w~
The y.~ of a E~LiÇ~lY apolar liguid c~n be found by contact angle ma~urement~ ~lth an apolar ~ur~ac~ ~at~ri~1 u~ing the equation~

1 + co.~ 5 2~y~7~J~ (5) where, Y T Y ~

Unlike apolar interactions, polar interactions are essentially asymmetrical and can only be satisfactor~ly treated by taXing that asymmetry into account, dividing up the polar co~ponent y~n of the sur~acs ten~ion into elec-tron acceptor y~ and electron donor y- para~eters~
The Young-Dupre equation c~n be exprsssed a~

YT ( 1 + C OSI~ AGD
where, ~ Gg.~w + ~G,~ ( ) 30 i5 the total free energy of interaction between a ~olid and a liquid. The polar and non-polar components of the free energy of interaction are:

~G~ = y~T ~D _ Y8AD _ Y ~ ( 8) ~G w = y w _ y TW _ y~ ~ = [(y~ w)~ _ (y~ W~ (10) Y;T Y ~ + YT ~ 2 [ ( YJ ~ Y ~ ) ~ +

9 6 3 ~

(Y59- y~ ' ) ~

From Eqn. (6) and taking into account Eqn~ (7)-(11):
y~ cosO ~ 2~ w ~ w)~ ' r ~~ +
(Y~ Y~ )~]. 1l2~

Thus, by contact angle ~asurement ~ith three di~er-ent liqu$ds (of which two muslt be polar) ~ith known y~
y~, and y~~ values, using ~n. (12) three ti~efi, then th~
~D W~ Y~l ~ r~~ 0~ any solid can be deter~ined. Simil~rly, by contac~ angle measurement of a li~uld on v~riou~ solid~
(o~ ~hich ~wo ~u~t be polar), the ~w, yy~, ana ~- c~n b~
determined. Thu~, wit~ the surr~ce tension paramet0r~ ~o~-sured, the free energy of inter~ction can be calcul~ted u~-ing Eqns. (7)-(9). The goal thus is to select a sur~actant solution thst will take the contact angle towards 180 and lift the contaminant o~f the soil matrixO

~ -The determination of total surface ten6ion and th~
non-polar component of surface tension o~ Aroclor 1248, which is a Pca con~ained in some hydraulic ~luid, is rela-tively stra~ght-forward. The mea~ure~ent of th~ ~ewi~
acid base parame~ers of ~he polar surface tension componen~
proved somewhat more dif~icult. ~wo independent exp4r~-m~nts were made. The pendant drop ~ethod w~ used to de-termine the total surface tension of the Aroclor 1248. ~he shape o~ the drop results from the interplay between the gravitational force, which is pulli~g on the drop and ~x-tending it, and the surface tension, which tends to make the drop spherical. The ~ethod is a conventional one, and is describ~cl in texts relating to the physical chemistry o~
surfaces (see, e.g., Adamson, Physiçal Chémistry Q~ S~r~aG-ç~, 4th ~d., Section II-9A, Wiley-Interscience). Two drops were photographed and measured. One o~ the calculations is reproduced below.

2~8~3~

The sl~e and shape o~ the drop are determined by two parBmeter~: one is the~w~dth (in cm) o~ the drop at the widest point (d~) and ths other i3 th~ width o~ the drop mea~ured at ~ distance d~ fro~ the botto~ o~ the drop.
These values determine ~ para~eter, 1/H, de~cribing the shape of the drop:

y = (~pgdo3)/H.

The average value for the two drops was 42.8 mJ~
The Lif~hit~-v~n der ~aals co~ponent of the surrace tension, y~W, was detax~in2d ~ro~ cont~ct angl~ ~e~sure-~ents on a ~mooth ~luoro~thylene poly~r ~r~ . Sev~r~l drops were measured and ~ultipls ~easure~ntæ o~ each drop wer~ made. The average contact angle was ~ound to ~e 81.3-. The Young'~ equation for an apolar ~olid is:

( 1 t COS~ ) Y T ~ = 2 ( 1 ~W Y :L.W ) ~ 3 ) and y8T-w _ 17.9 ~J~m~. The Aroclor 1248 has y~w = 34 mJ/m~ and, from 1~ = yr W ,1, y~ D

it iB clear that the polar compon~nt o~ th~ 6ur~ace tension y~ i8 8 .9 ~IJ/ml.
The L2wi~ acid-base para~eters are r~lated to the po-lar co~ponant, y~, by:
r~ = 2(y~ y~)~.

The complete Young's equation ~or apolar materials is (1 + cos~)yT~o~ = 2(y~W yT~ + (y~ y~ )~9 + (y~ ~

3 ~

Two polar substra~as wers u~sd to esti~ate the polar surface t~nsion parameters; polystyrene (PS~ and pol~msth-ylmetha~rylate (PMMA). Their surface ten~ion components are set forth in Table III below.
s Table III. Surface Tension Co~p~n~nt~.

Surface Tsnsion.

y~w 43.9 47.0 y+ O O
y_ 2.~ 22.

Polystyrene is less useful than P~ becau~e it has a small y~; both are monopolar substances. Tbis monopolarity makes it possible to solve for y' and r~ ~or Aroclor 1248 given th~ value of y~. The average contact an~le of Aro-clor 1248 on PMMA is 23.8-, giving Ys' - 11.4 ~ . From the value 9~ y~ ~' of 8.9 mJ/m~ yi~ld~ y~- = 1.7 mJJ~. ~he average contact angle on polystyrene ~as 17.9~ and a simi-lar calculation ~as done. The results of ~hese calcula-tions based on the contact ~ngles of Aro~lor 1248 on thes~
two substrates are set forth in Table IV below.

Table IV. Polar Surface Tension Values for Aroclor 1248.
3~
~ PMM~ Geome~ric ~ean y+ 3.8 71.4 6.6 y- 5.2 1.7 3.~) ==______==================== ==========================

Given the limited measurements that can be made of Aroclor 1248 liquid on well-characterized solid substrat2s, 2~9~3~

there 1~ ~ome uncert~in~y associ~ted with thes~ vnlues, but that i5 lnherent in studies of the sur~ac0 tension o~
quids. It ls much easier, and the results are more cer-tain, ~o measure the surr~ce tension components of solid surfacas because a variety o~ di~rent liquids may ~e used.
A second attempt to ~st;lmat~ th~ polar componant oP
the surfac~ tension was made using comDercl~lly-available PARAFIL~, which i~ ~ non-pola:r p~ra~in material with y~~
= y~w = 2~.5 mJ/m~. The aveIage contact anyl~ o~ Aroclor 1248 on this m~terial was 51.2 , giving y~~ ~ 38.6 and YYC~ = 4.3 mJ/~. Thi~ a sm~ r v~lue ~or ~he component, which i~ ~ore in lln~ wi~h ~he expect~d propar-~ies for this ~teri~l. It should b~ noted, howev~r, ~hat use of these values with th~ cont~ct ~ngles ~or Aroclor 1248 on PMM~ yielded a small y~ but a very larg~ y~ (about 40 m~/m2). ~his is not consistent with the low solubility of PC8.
As a ~inal and independent analysis o~ ~he sur~ace tension components of Aroclor 1248, the solubility in water of this ~aterial may be utilised. Some assumption~ were made about Aroclor 1248, na~ely, that it i~ a monopolar liquid with a y' = 0 and y~ = 42.9 ~Jfm3 ~ The value o~
the solubility used was 1 ppm. Fro~ polymer ~olubility studies, it is known tha~ the in~2rfaci~1 frae energy i~
rslated to the solubility by the ~ollowing relation:

~G ~a = -kT ln(l/S~, (15) ~here S is the ~olubility in moles~liter (M~, k is the Boltzmann constant, and T is the tempPrature in Kelvin.
Summarizing the contact anqle data which are the most reliable:
Summary of PCB experiments-~c~ = 20.4 on PMMA
¢~W~Q~ = 66~3 on PMMA
~ o~n~m~ = 51 ~9 on P~IA
.

20~9~3~

and given the v~lue~ ~or PMMA, y ~ ~ 42.0, y' ~ 0.0, y~
16.7.
It i~ reasonabla to as~ume that ~roclor 1248 i8 non-polar (y~ y~ ~ 43.6 mJJ~n', slightly largar th~n the pendent drop measurements indiicated, thQn y~ ~ o ~J/~2 ~ .
The ~olub~lity (S) is approximately 1 pp~, the ~olecu-lar weight (HW) ls approximately 360, the contactable ~ur-face area fSc) i6 approxl~ately 0.8 n~' (e8timated ~ro~
twice the ~c value ~or ylucose!). Sub~ti~utlng ln the v~l-ues of S ( 1 ppm or 2 . 78xlO-' H), k ( 1. 38xlO-'' J/IC~ and T
(300K) in Eqn. (15) give~; ~G ~ 4.7 ergs/cDI~ or n~/~.
Frs:m ~Gl tl ~ -2y~ 2, valua o~ Y L~ ~ 32 . 3 32~ re~
sult~.
Using w ) ~ -- ~ y~t~ w ) ~ ~ ~ + 2 [ ( y~pO~ Yl?.,~ ) + ( Yw~s~ Yw~eo~ ) ( ~ Yw~so~ ) ( YPO~ ~ ~e~~

and entering the values which are known for water and tho8e which have been derived ~or Aroclor 1248 yields (43.~)~ - r~1.8~]~ + 2[(0 x y~O~ +
(25.5 x 25.5)~ x 25.5)~
- (D x 25.5)~]

From the solubility data, it is independently kno~n that y ~ = 35.75 mJ/ma, so this all~w8 solving ~or the val-ue ~ Y~c~- (= 3-5 ~J~m'). The following Table IV liRt values o~ Y~c~~ for different value~ o~ th2 solubility.

~ ==~=======_=======3=~a~=~=_- =5== - ~==~= - 3==_=ea Table IV. Interfacl~l Ten~ion betwe~n Aroclox 1248 and Water (Y~ nd ~awis Bas~
Co~ponant: of Aroclor 1248 (Y~cn ) Versus Solubility.

~ Y~o~~
0.1 ppm 38.2 2.7 1.0 pp~ 32.3 4.9 10.0 pp~ 26.5 7.8 For a s~aller v~lu~ of Sc S0.6 n~a), ~nd S ~ 1 ppD~
then rl, = 43.1 ~nd Y~c~ 3 ~J~ma.
Thus, the best e timate ~or ~he sur~ace tension co~-ponents o~ Aroclor 1~48 from ~ combination of contact angle measurements and solubility is given in Table V, below.

======= = _ _==,. ===== _ _ _= _ _ _ _ Tahle V. Surface Tension Components for Aroclor 124B.

y~C~ r 43 . 4 mJ~'m~
y ~ 43,4 mJ/~
y~_~ 0 ~CD O
Y~c~ 4.g ~J~
==__========_=__========== = __===_= = =_= _ = =

III. netermiaatiOn of ~he In~r~ial ~naion be~een Contaminant and Surfac~ant and the Çri~e ~ ~or ~urfactan~
SeleC~iQn The next part of the method o the invention is to determine t~e interfacial energy of the surfactant and the pollutant of interest. ~he interfacial tension between two liquids is measuxed ~y a variety of approaches, such as 6 ~ ~

hsnging drop, spinning drop, ~d drop weight method. By making use of Y~ ~(Y ~ ~ (Y~ )~] + 2[(y~ +
(Ya Y ;~ a ~ ~ + (1~1 Y3 ) ~ ~ (16) one can obtain ylT~ Yl~ and ~~ once th~ lntsrfaci~l t~n-s~on Yl~ ~etween this li9uid and three oth~r compl~t~ly charactsr~zed liquid~ are kno~l.
Surfactant polar (~ ~nd ~ nd non-pol~r (y'~) ~ur-face tension component~ are then listed bas~d upon che~ic~l structur~, Thi~ methodology, 6hown b~low, reve~ls th~
three surface ten6ion co~onent~ re~uir~d gor b~th~th~ po-lar ~hydropAil~c~ and the non-pol~r Illpophilia) p~rts o~
the ~ur~actant molecule. Thus, iP th~ s~r~ac~ tension val-ues ~or N polar groups and M non-polar group~ are kno~n, then estimates for N*M sur~actant co~bination~ can be ~ade.
This gives one th2 ability to fine-tune ~ur~ce ten~ion re-quirements and to design surfactants for conta~inant r~mov-al.

One Surfactant HYDROPHILE - LIPO~IILE
~ydrophilic Group + Llpophili~ ~roup And six surfac2 ten~ion ~easurements:
three ~or: (~ ~, y~ , ~8- ) ~nd three ~or~ , y~ , yT.~~

Gives (y~_ ~w, y~_T~, y~_,~) for the surfactant.
_ _=====__======= ~ ==_=========a=====__ =====~==

The ~G,p,~TT betwe~n the contaminant, or pollutant 35 (p), and so:il, or mineral (m), is computed from Eqn. ~7~
for each con~ination. The ~G,,~T between the surf~ctant (s) and pollutant can also be determined.

2 ~

When ~G",p ~ ~G ~ro~

then tha contaminant pref~rs to ~tick to the ~ ctant rather than ths ~oil. Addltiorlally, 3ur~actant~ selected should hold to the criteria ~G ~~
O
so that the surfactant will not pr~3ferenti~lly tick to the soil, ~us interfering in the extr~lction proc~s.

ca~l~ ~or In~¢2~ci~
The relevant sur~as:e tsnsion valuaB itor water are: y = 72.8, ~w = 21.8, y~ = 25.5, and y~ - 25.5 ~/m~ and for hexane are: y = 18 . 4, ~ 1 = 18 . 4, y ' - 0, and y~ = 0 . The values for quartz are: yTW = 39.9, y ' = O, and y~ = 25 mJ~m'. The value~ for Aroclor 1248 are given in Table V
above . The inter~acial tension is given ~ro~ Eqn . ~16 ) above by:
y = ~y ~W)~ -- (y~,tO~W)'3]~ + 2[(y~ l~o~ ) + ( ~w~ Yw~ Y~
+ ~ Y~O~ Y~.. ~._ ~ ]
The Dupre equation gives the ~ree energy o~ adhesion:

AG 3~ - Y~2 ~ Y 3 - Y33^

Table VI below sets ~orth the adhesion ener~y of Aroclor 124~ to quartz in the presence of (a) water and (b) hexane.

2~8~

~ w===-_====~==~=- ~==========:===~3_~=~ ss==a=~
Table vI. Adhe6ion Energy o~ ~roclor 1248 to Qu~rtz in ths Presence o~ Wat~r and Hexane.

Yl~ 32.3 mJ/~ Int2rfacial tension bet~een between Aroclor 1248 (1) and water (2) ~G,~ ,T'r -35c5 :Free en~rgy o~ ~dhe5ion t~a-tween Aroclor ~248 (2) and Iquartz (1) in th~ pre~ence Or w~er ( 3 ) ~~ - 9.3 Free energy o~ ~dhesion be-tween Aroclor 1248 (2) and quartz (1~ in tha presence of hexane ( 3 ) --============~ = _========= _ ===_ _= ._ In Table VI, one oan sae that there is a substanti~l adhesion energy between th~ Aroclor 1248 and quart~, a com-mon constituent in soils, in ~he pre6ence o~ wat~r. I~ th9 water were replaced by hexan~, the adhesion energy i8 5ub-stantially reducsd, but i5 still negative, which ~ean~ ~h~t the ~roclor will still bind to the gu~rt2.
Perfor~ing the sa~e typs of c~lculatio~s with a ~uit-able surfactant would reveal whether that sur~actant created a positive adhesion energy, by which would ~ean that the Aroclor (or conta~inant~ ~ould no longer b~nd to the quartz. That surfactant could then be use~ul in treating a soil polluted with the contaminant.

IV. Im~Q~ nt. ~ Sur~actan~ Action b~_~he ~d~ition of a Co-~ur~actant.
~ubsequent to characterizatio~ of the polar and non polar contributions to interfacial tensions in the soil-contaminant system, it is possible to improve the adhasion 21 ~9~3~
between surfactant and pollutant by ~eeding th~ ~oil ~lth an oil ~oluble co-surfactant.
The sur~ac~ tension co~ponent5 whlch h~ve been det~r-mined by contact angle ~easurement~ giYe para~eters for the co-surfactant. For exampl0, i~ the cont~minAnt i~ l~rgely apolar, (large y~ component), then a desirable comblnat~on of surfactant and oil-soluble co-~urfactant would be a ~ur-~actant which is largely basic in nature and a co 6ur~ac-tant which is larqely acidic in nature. ln order to have ef~ective removal, the ~urfactant-co-surfact~nt pair ~ust be chosen in such a way that t:he soil-contaminant contact anç~ls gses to 1 0 when the sur~ct~nt solutlorl i~ add~ to tha cont~minant ~;o$1, ~us li~ting tbe contaminant o~2 th~
60il compl~3tely. Tha s:o-sur~actnnt provld~ ~n addition~l set of parameters whereby th~ s migh~ be acco~plished.

The method of the invention is expected to find use in the extraction of chemical pollutants from contaminated soils.

Claims (10)

What Is Claimed Is:

1. A method for selecting a surfactant for the extrac-tion of chemical pollutants from soils having at least one mineral component comprising:
(a) characterizing the soil;
(b) determining the surface energies of the pol-lutant and the soil; and (c) estimating the chemical nature of the surfac-tant which would provide removal from the soil.

2. The method of Claim 1 wherein said soil is charac-terized by determining the mineral character thereof.

3. The method of Claim 2 wherein the mineral character is determined by identifying minerals that make up the soil and their concentration.

4. The method of Claim 1 wherein the surface energies of the pollutant and the soil are determined either (I) by making measurements of the contact angle between (a) the pollutant and three surfaces: a first surface suitable for providing a measure of the non-polar component of surface tension, .gamma.LW, a second surface suitable for providing a measure of the polar, Lewis acid component of surface ten-sion, .gamma.+, and a third surface suitable for providing a mea-sure of the polar, Lewis base component of surface tension, .gamma.-, and (b) at least one mineral component of the soil and three different liquids, of which two must be polar, with known values of the Lifshitz-van der Waals and the positive and negative Lewis acid-base components of surface tension or (II) by calculating the interfacial tension with the known non-polar and positive and negative Lewis acid-base surface tension components.

5. The method of Claim 1 wherein the chemical nature of the surfactant which would remove the pollutant from the soil is estimated by (1) determining the interfacial energy of the surfactant and the pollutant and (2) selecting the surfactant to extract chemical pollutants if (a) the free energy of the surfactant/pollutant is greater than the free energy of the pollutant/soil and (b) the free energy of the surfactant/pollutant is greater than the free energy of the surfactant/soil, all based on the interfacial energies.

6. A method for extracting chemical pollutants from contaminated soil comprising:
(a) selecting at least one surfactant for the extrac-tion of chemical pollutants from soils having at least one mineral component comprising:
(1) characterizing the soil, (2) determining the surface energies of the pol-lutant and the soil, and (3) estimating the chemical nature of the surfac-tant which would provide removal from the soil; and (b) treating said contaminated soil with said at least one surfactant.

7. The method of Claim wherein said soil is ]
terized by determining the mineral character thereof.

8. The method of Claim 7 wherein the mineral character is determined by identifying minerals that make up the soil and their concentration.

9. The method of Claim 6 wherein the surface energies of the pollutant and the soil are determined either (I) by making measurements of the contact angle between (a) the pollutant and three surfaces: a first surface suitable for providing a measure of the non-polar component of surface tension, a second surface suitable for providing a measure of the polar, Lewis acid component of surface tension, and a third surface suitable for providing a measure of the po-lar, Lewis base component of surface tension and (b) at least one mineral component of the soil and three different liquids, of which two must be polar, with known values of the Lifshitz-van der Waals and the positive and negative Lewis acid-base components of surface tension or (II) by calculating the interfacial tension with the known non polar and positive and negative Lewis acid-base surface tension components.

10. The method of Claim 6 wherein the chemical natur-of the surfactant which would remove the pollutant from the soil is estimated by (1) determining the interfacial energy of the surfactant and the pollutant and (2) selecting the surfactant to extract chemical pollutants if (a) the free energy of the surfactant/pollutant is greater than the free energy of the pollutant/soil and (b) the free energy of the surfactant/pollutant is greater than the free energy of the surfactant/soil, all based on the interfacial energies.