WO1993004356A1

WO1993004356A1 - Surfactant selection method for the extraction of chemical pollutants from soils

Info

Publication number: WO1993004356A1
Application number: PCT/US1992/005176
Authority: WO
Inventors: Lauren M. Purcell; Albert F. Lawrence
Original assignee: Hughes Aircraft Co
Current assignee: Raytheon Co
Priority date: 1991-08-13
Filing date: 1992-06-22
Publication date: 1993-03-04
Anticipated expiration: 1994-02-13
Also published as: EP0552327A1; JPH06502124A; CA2089639A1; KR930702668A

Abstract

The physics of adhesion are applied to choosing surfactants that have Lewis acid-base and dispersion force interaction 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-surfactant to improve the adhesion between a surfactant and a pollutant.

Description

SURFACTANT SELECTION METHOD FOR THE

EXTRACTION OF CHEMICAL POLLUTANTS FROM SOILS

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to the extraction of chemical pollutants from the soil, and, more particularly, to the selection of specific surfactants to extract specific pollutants from a given soil.

2. Description of Related Art

The clean-up of all the hazardous waste sites in America is an enormous task. Not only is the number of sites growing each year, but also the clean-up of the sites is difficult both technologically and economically. The number of CERCLA (Comprehensive Environmental Resource Conservation Liability Act) Superfund sites on the National Priority List is large (1,236 at the present time) and growing each day. Increasing legal restrictions on clean-up practices make it even more difficult to comply with responsibilities. Landfills no longer accept hazardous wastes. Soil aeration is prohibited in most populated regions. Pump and treat methods have been ineffective in many cases. Rules against burying and discarding wastes have proliferated. Treatment plans and schedules must be submitted to the EPA, the local agencies, and to the public for approval, which can impose more constraints on remediation choices.

In response to increased environmental concern, numerous innovative clean-up technologies have been proposed by both public agencies and private companies. Table I below shows extraction and destruction techniques which have been proposed for polychlorinated biphenyls (PCBs). Extraction and destruction of toxic chemicals are accomplished through chemical, thermal, or mechanical means. A cost effective combination of both extraction and destruction is desired. Effectiveness and cost considerations are high on the list of priorities, so any proposed clean-up approach must be more effective and cost less than existing technologies.

The difficulty in cleaning contaminated soils today is that, depending on the contaminant, acceptable contamination limits are in the range of parts per million or less. Most of the technologies currently used in soil remediation are either not capable of meeting these standards or are not feasible for economic reasons.

Very high concentration sludges may be effectively decontaminated by thermal destruction techniques such as incineration, or plasma torch, or electron beam irradiation. But low level contamination spread out over hundreds of thousands of cubic yards of soil requires other, less costly methods. Here, chemical or biological treatment technologies would take longer, but would cost orders of magnitude less than incineration. Although bioremediation is difficult to engineer, both bioremediation and soil washing impose the least harm to the environment. These latter techniques are also potentially the least costly. Current technology can be used to enhance these techniques so they can reduce contamination to the regulated levels.

Like all remediation techniques, surfactant treatment also has its advantages and disadvantages. It is inexpen- sive, non-toxic, and removes and concentrates pollutants before destruction. However, although extraction takes place, there is no destruction of the contaminant, the in situ extraction process can be slow, and removal of large contaminant concentrations can be impeded unless large scale earthmoving, grinding, and mixing operations are performed. Many experiments rely on solubility to predict performance, only to find that upon application to a real site, solubilization of pollutants varies dramatically with soil conditions. Thus, some surfactants are not as effec- tive in the field as expected based on lab analysis. Other problems which emerge in field tests are enough to stop pursuits with this technology.

The distribution of contaminants in soils depends upon the porosity of the soil and the actual mineral content of the soil. Contaminants adhere to soil constituents with varying strengths. Presently available are a variety of practical and empirically-derived tools which provide yardstick measurements to surfactant performance. Some of these tools include hydrophilic-lipophilic balance (HLB) values, solubility results, previous experimental results, etc. The problem with these tools is that they all require numerous experimental tests of a variety of surfactants, most of which are chemical formulations of unknown (to the user) compounds. The use of physical models helps to provide a more realistic and quantifiable understanding of surfactant action. A coherent evaluation of the chemistry and physics of adhesion can reduce, if not eliminate, poor surfactant selections.

Thus, a need remains for a predictable method of determining the appropriate approach to removing contaminants in the soil using surfactants. SUMMARY OF THE INVENTION

In accordance with the invention, a method is provided for selecting the appropriate surfactant, or surfactants, for the removal of a given contaminant from a specific soil. There are three aspects to surfactant selection: characterization of the soil, contact angle measurements to determine the surface energies of pollutants on soils, and estimation of the chemical nature of the surfactant which would provide effective removal.

Application of the method of the invention characterizes the polar and non-polar contributions of the surfactants needed to extract the particular contaminant from the soil . The structure of the surfactant is dictated from these polar and non-polar forces. Selection of surfactants can be predicted from the actual chemistry of the soil-pollutant system, thus reducing time and effort spent on numerous experimental trials. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram depicting the solubility and formation of micelles;

FIG. 2 is a cross-sectional view, depicting a drop of liquid on a solid surface, and showing the contact angle; and

FIGS. 3a and 3b are schematic diagrams depicting the significance of contact angles in oil removal. DESCRIPTION OF THE PREFERRED EMBODIMENTS

Solubilization of contaminants is a multi-stage physical process. FIG. 1 schematically depicts the roll-back mechanism for removal of oil 10 which is adhered to rock 12. The oil 10 is surrounded by surfactant molecules 14 oriented so that the lipophilic end 14a lines up towards the oil 10, while the hydrophilic end 14b is surrounded by water (which surrounds the assembly shown in FIG. 1, but which is not depicted). The surfactant 14 acts to initiate drop formation, followed by necking and eventual oil removal and the formation of micelles.

The present invention is directed to the initial release rather than the formation of micelles in solution. In particular, the present invention is directed to the selection of one or more appropriate surfactants to remove contaminant(s) from a given soil.

There are three aspects to surfactant selection: characterization of the soil, contact angle measurements to determine the surface energies of pollutants on soils, and estimation of the chemical nature of the surfactant which would provide effective removal.

Specifically, a full characterization of the contaminated site soil mineralogy is required. Then, measurements of the contact angle between the contaminants of interest and three types of surfaces are necessary. These measurements provide the surface tension contributions to the interaction energy between the contaminant and the soil. To determine the adhesive force between surfactants and contaminant, interfacial energy measurements between surfactant (polar and non-polar groups) and test surfaces must be made. The test surfaces may be the same as those for determining the interaction energy between the contaminant and the soil or they may be different. The important aspect is to obtain well-defined values.

Interfacial tension between surfactants and the soil can be computed to assist in evaluating whether selected surfactants may adhere to soils. Surfactant non-polar and polar surface tension contributions (based on surfactant chemical structures) are evaluated in terms of the total free energy of interaction between the contaminant and surfactant versus contaminant and soil to predict the performance of existing and novel surfactant molecules.

Application of the method of the invention will characterize the polar and non-polar contributions of the sur factants needed to extract the particular contaminant from the soil. The structure of the surfactant will be dictated from these polar and non-polar forces. Selection of surfactants can be predicted from the actual chemistry of the soil-pollutant system, thus reducing time and effort spent on numerous experimental trials.

Interactions of surfactants with clays, silica, and other soil minerals can be predicted from the teachings of this invention.

The surfactant selection methodology is described below. It includes contributions from surface chemistry and applies them to surfactant performance for the remediation of soils. The method of the invention provides for both the determination of the surface adhesive forces between the contaminant of interest and the soils in which the contaminant(s) lie, and the determination of the surface adhesive forces between the surfactant and contaminant and between the surfactant and soils.

Having selected the surfactant (or combination of surfactants) based on the teachings herein, any of the well-known in situ and on-site reactor soil remediation processes and apparatus may be employed to treat the contaminated soil. These extraction processes and apparatus are well-known and do not form a part of this invention, which is directed to the selection of the surfactant(s) used to treat the contaminated soil.

I. Soil Characterization.

The first step is to determine the mineral character of the soil. Mineralogy is needed to determine the adhesive energy between the soil and the pollutant. The adhesive energy is the force which must be overcome by the surfactant to remove the contaminant.

The principal tool for this work, X-ray diffraction, can be found in typical mineralogy laboratories. Typically, minerals are identified, together with how their composition varies with particle size. For example, there are coarse, medium, and fine grained silicas; however, in soils, clays are typically finer grained than silicas.

For example, a Siemens D-500 diffractometer, driven by a DEC Microvax computer and equipped with a copper anode X- ray tube operating at 40 KV and 30 mA, is suitably employed in soil analysis. A graphite diffracted-beam monochromator is positioned between the sample and the detector. Analysis is done grinding the soil sample to pass a 350 mesh screen and then recording the diffraction pattern. The patterns are identified through a JCPDS (Joint Committee on Powder Diffraction Standards) Powder Diffraction File stored on computer. Search is both automatic using Siemens software and manual by visual inspection. Each constituent mineral phase present in quantities greater than 5% by volume can be identified.

A sample from a PCB-contaminated site was taken and dispersed in distilled water. Two fractions of soil were taken based on particle size which were, roughly, the clay (fine) fraction and the coarser fraction. The fine fraction was deposited on a glass slide using a conventional technique for clay mineral analysis. The coarse fraction was packed in a bulk sample container. The diffraction patterns for both were similar, indicating that both contain essentially the same minerals, but not necessarily in the same proportions.

The dominant mineral was quartz, with minor amounts of other silicates. This mineralogy, listed in Table II, is typical of a soil derived from glacial sediments and reflects the igneous rock types in Canada, the source of these sediments.

II. Determination of Contaminant-to-Soil Adhesion.

Determining the interfacial polar and non-polar interactions between solids and liquids is known; see, e.g., C.J. Van Oss et al, "Interfacial Lifshitz - van der Waals and Polar Interactions in Macroscopic Systems", Chemical Reviews, Vol. 88, No. 6, pp. 927-941 (1988). Further, determining the acid-base interactions between clay minerals and human serum albumin in aqueous media through a series of contact angle measurements is also known; see, e.g., P.M. Costanzo et al, "Determination of the acid-base characteristics of clay mineral surfaces by contact angle measurements", Journal of Adhesion Science and Technology, Vol. 4, No. 4, pp. 267-275 (1990).

The inventors have discovered that the foregoing procedures can be applied to the treatment of contaminated soil with surfactants.

A. Contact Angle Measurements.

Young's equation, which defines the surface tension (γ_SL) between a solid (S) and liquid (L), can be computed from measuring the contact angle (FIG. 2), given the surface tension between the solid and air (γ_SA) and the liquid and air (γ_LA): γ_SL = γ_SA - γ_LA COSΦ (1)

FIG. 2 shows the contact angle Φ which a drop 20 of liquid makes with a surface 22.

Contact angle provides a measure of wettability. As shown in FIG. 3a, in a water-oil-silica system (the water is not shown in the drawing, but surrounds the assembly), oil 10 does not spread on (wet) the substrate 12, but will form a finite contact angle in water. FIG. 3b shows that the surfactant solution (again, not shown) in place of water reduces the surface tension between the substrate 12 and the oil 10 , enough to pull the oil into solution . During soil washing, the surfactant bath will spontaneously displace the oil from the substrate when the contact angle is 180°; if the contact angle is less than 180° but more than 90°, the contaminant will not be displaced spontaneously but might be removed by hydraulic currents in the bath. When the contact angle is less than 90°, at least part of the contaminant will remain attached to the substrate. In oil-water systems, hydrogen bonding plays a significant role in the oil-water surface tension and the interaction with the substrate, thus the separation of polar and non-polar contributions is needed.

In order to calculate the free energy of adhesion of the contaminant with the solid substrate (or soil), one must obtain independent surface tension values which are divided into non-polar (Lifshitz-van der Waals: LW) and polar (Lewis acid-base: AB) surface tension values. A total of three values are determined for each contaminant and soil mineral type. One of the three values is based upon the non-polar dispersion forces of interaction defined by Lifshitz-van der Waals theory and the other two values are based upon two polar forces of interaction defined by the electron donor and electron acceptor definitions of Lewis acid-base theory.

The total surface tension of a given material is the sum of its polar and non-polar components: γ = γ^LW + γ^AB (2) where,

γ^LW = Lifshitz-van der Waals contribution γ^AB = 2(γ⁺γ-)^½ = Lewis acid-base contribution γ⁺ = Lewis acid surface tension contribution (electron acceptor) γ- = Lewis base surface tension contribution (electron donor).

Experimentalists use total surface tension as one of their yardsticks in predicting solubilization. Additional valuable information can be obtained from the division of surface tension into its three chemically significant components, Lifshitz-van der Waals and the positive and negative Lewis acid-base components. The three separate ener- gies are related in the following equation for interfacial tension between two substances (γ₁₂): γ₁₂= [ (γ₁ ^LW)^½ - (γ₂ ^LW)^½ ]²+2[(γ₁+γ₁-)^½+

( γ₂+ γ₂ -) ^½ - (γ₁ ⁺ γ₂-) ^½ - (γ₁- γ₂ ⁺)^½] (3)

The significance of this equation is the acid-base interaction parameters. Not only are the acid-base interactions between different molecules given, but also the acid- base interaction with itself.

The total surface tension of liquids can be measured or found in published tables. If measured, three different surfaces are employed, such as a polytetrafluoroethylene material for the non-polar component and polymethylmethac- rylate for the polar (Lewis base) component). There are no reliable solid surfaces with a large polar (Lewis acid) component. Thus, the Lewis acid component of the liquid must be computed from measurements on another surface with a different Lewis base value, such as polystyrene.

The desired surfaces will be in either a solid, smooth crystal form or prepared in a pressed cake with a smooth surface which can be reliably reproduced. All surfaces must have known γ^LW, γ⁺, and γ- values.

Once the total surface tension is known, the γ_L ^LW can be found by one of two methods. One method is that of Lif- shitz as described by D.B. Hough et al, "The Calculation of Hamaker Constants from Lifshitz Theory with Applications to Wetting Theory", Advances in Colloid and Interface Science, Vol. 14, pp. 3-41 (1980), where the dispersion forces between bulk materials is found from the dielectric of the materials in question,, the refractive index, etc.

Another method is by measuring contact angles of the (partly polar) liquid on a solid non-polar substrate, such as polytetrafluoroethylene or other fluoroethylene polymer, knowing the value of γ_S ^LW and using the equation: γ_L(1 + cosΦ) = 2(γ_S ^LW γ_L ^LW )^½. (4)

The γ_L ^LM of a strictly apolar liquid can be found, by contact angle measurements with an apolar surface material using the equation: 1 + cosΦ = 2(γ_S ^LW /γ_L)½ (5) where,

γ_L = γ_{L LW.}

Unlike apolar interactions, polar interactions are essentially asymmetrical and can only be satisfactorily treated by taking that asymmetry into account, dividing up the polar component γ^AB of the surface tension into electron acceptor γ⁺ and electron donor γ- parameters.

The Young-Dupre equation can be expressed as γ_L(1 + cosΦ) = -ΔG_SL ^TOT (6) where,

ΔG_SL ^TOT = ΔG_SL ^LW + ΔG_SL ^AB (7) is the total free energy of interaction between a solid and a liquid. The polar and non-polar components of the free energy of interaction are:

ΔG_SL ^AB = γ_SL ^AB - γ_S ^AB - γ_L ^AB (8) ΔG_SL ^LW = γ_SL ^LW - γ_S ^L _W - γ_L ^Lw (9)

Y_SL ^LW = [(γ_S ^LW )^½ - (γ_L ^LW )^½]² (10) γ _{S L} ^AB = γ_S ^AB + γ_L ^AB - 2[(γ_S+ γ_L-)^½ + (γ_S ^_ γ_L+) ½ ] . (11)

From Eqn. (6) and taking into account Eqns. (7)-(11): γ_L(1 + cosΦ) = 2[(γ_S ^LW γ_L ^LW) ^½ + (γ_S+ γ_L-)^½ +

(γ_S- γ_L+ )^½]. (12)

Thus, by contact angle measurement with three different liquids (of which two must be polar) with known γ_L ^LW, γ_L ⁺, and γ_L- values, using Eqn. (12) three times, then the γ_S ^{L W}, γ_S+, γ_S- of any solid can be determined. Similarly, by contact angle measurement of a liquid on various solids (of which two must be polar), the γ_L ^LW, γ_L ⁺, and γ_L- can be determined. Thus, with the surface tension parameters mea- sured, the free energy of interaction can be calculated using Eqns. (7)-(9). The goal thus is to select a surfactant solution that will take the contact angle towards 180° and lift the contaminant off the soil matrix. B. Example of Contact Angle Measurement.

The determination of total surface tension and the non-polar component of surface tension of Aroclor 1248, which is a PCB contained in some hydraulic fluid, is relatively straight-forward. The measurement of the Lewis acid-base parameters of the polar surface tension component proved somewhat more difficult. Two independent experiments were made. The pendant drop method was used to determine the total surface tension of the Aroclor 1248. The shape of the drop results from the interplay between the gravitational force, which is pulling on the drop and extending it, and the surface tension, which tends to make the drop spherical. The method is a conventional one, and is described in texts relating to the physical chemistry of surfaces (see, e.g., Adamson, Physical Chemistry of Surfac- es, 4th Ed., Section II-9A, Wiley-Interscience). Two drops were photographed and measured. One of the calculations is reproduced below. The size and shape of the drop are determined by two parameters: one is the width (in cm) of the drop at the widest point (d_e) and the other is the width of the drop measured at a distance d_S from the bottom of the drop. These values determine a parameter, 1/H, describing the shape of the drop: γ = (Δpgd_e ²)/H. The average value for the two drops was 42.8 mJ/m².

The Lifshitz-van der Waals component of the surface tension, γ^LW , was determined from contact angle measurements on a smooth fluoroethylene polymer surface. Several drops were measured and multiple measurements of each drop were made. The average contact angle was found to be 81.3°. The Young's equation for an apolar solid is:

(1 + cosΦ ) γ_L ^T _OT = 2(γ_S ^LW γ_L ^LW) ^½ (13) and Y_S ^LW = 17.9 mJ/m². The Aroclor 1248 has γ_L ^LW = 34 mJ/m² and, from γ = γ^LW + γ^{AB ,} it is clear that the polar component of the surface tension γ^AB is 8.9 mJ/m².

The Lewis acid-base parameters are related to the polar component, γ^AB, by: γ^AB = 2(γ⁺ γ- ) ^½ .

The complete Young's equation for apolar materials is

(1 + cosΦ)γ_L ^TOT = 2(γ_S ^LW γ_L ^LW)^½ + (γ_S ⁺ Y_L-)^½

+ (γ_L+ γ_S- ) ^½ (14) Two polar substrates were used to estimate the polar surface tension parameters; polystyrene (PS) and polymeth- ylmethacrylate (PMMA). Their surface tension components are set forth in Table III below.

Polystyrene is less useful than PMMA because it has a small γ-; both are monopolar substances. This monopolarity makes it possible to solve for γ⁺ and γ- for Aroclor 1248 given the value of γ^AB. The average contact angle of Aroclor 1248 on PMMA is 23.8°, giving γ_L ⁺ = 11.4 mJ/m². From the value of γ_L ^AB of 8.9 mJ/m² yields γ_L- = 1.7 mJ/m². The average contact angle on polystyrene was 17.9° and a similar calculation was done. The results of these calculations based on the contact angles of Aroclor 1248 on these two substrates are set forth in Table IV below.

Given the limited measurements that can be made of Aroclor 1248 liquid on well-characterized solid substrates , there is some uncertainty associated with these values, but that is inherent in studies of the surface tension of liquids. It is much easier, and the results are more certain, to measure the surface tension components of solid surfaces because a variety of different liquids may be used.

A second attempt to estimate the polar component of the surface tension was made using commercially-available PARAFILM, which is a non-polar paraffin material with γ^TOT = γ^LW = 25.5 mJ/m². The average contact angle of Aroclor 1248 on this material was 51.2°, giving γ_PCB ^TOT = 38.6 and γ_PCB ^AB = 4.3 mJ/m². This is a smaller value for the AB component, which is more in line with the expected properties for this material. It should be noted, however, that use of these values with the contact angles for Aroclor 1248 on PMMA yielded a small γ⁺ but a very large γ- (about 40 mJ/m²). This is not consistent with the low solubility of PCB.

As a final and independent analysis of the surface tension components of Aroclor 1248, the solubility in water of this material may be utilized. Some assumptions were made about Aroclor 1248, namely, that it is a monopolar liquid with a γ⁺ = 0 and γ^LW = 42.9 mJ/m². The value of the solubility used was 1 ppm. From polymer solubility studies, it is known that the interfacial free energy is related to the solubility by the following relation:

ΔG₁₂₁ = -kT ln(1/S), (15) where S is the solubility in moles/liter (M), k is the Boltzmann constant, and T is the temperature in Kelvin. Summarizing the contact angle data which are the most reliable:

Summary of PCB experiments:

Φ_PCB = 20.4 on PMMA

Φ_water = 66.3 on PMMA

Φ_formamide = 51.9 on PMMA and given the values for PMMA, γ^LW = 42.0, γ⁺ = 0.0, γ- = 16.7.

It is reasonable to assume that Aroclor 1248 is non- polar (γ^TOT = γ^LW = 43.6 mJ/m², slightly larger than the pendent drop measurements indicated, then γ⁺ = 0 mJ/m²).

The solubility (S) is approximately 1 ppm, the molecular weight (MW) is approximately 360, the contactable surface area (Sc) is approximately 0.8 nm² (estimated from twice the Sc value for glucose). Substituting in the val- ues of S (1 ppm or 2.78x10^-6 M), k (1.38x10^-23 J/K) and T (300K) in Eqn. (15) gives ΔG₁₂₁ = -64.7 ergs/cm² or mJ/m².

From ΔG₁₂₁ = -2γ₁₂, a value of γ₁₂ = 32.3 mJ/m² results.

Using γ₁₂ = [(γ_Pcb ^LW)^½ - (Y_water ^LW)½ ]² + 2[(γ_pcb ⁺ γ_pcb-)^½

⁺ ( γ_water+ γ_water- ) ½ - (γ_pcb + γ_water-)½

- ( γ_pcb- γ_water ⁺)^½ ] and entering the values which are known for water and those which have been derived for Aroclor 1248 yields γ₁₂ = [(43.4)^½ - (21.8)^½]² + 2 [ ( 0 X γ_pcb- ) ^½ +

(25.5 X 25.5) ½ - (γ_pcb ⁺ X 25.5 )½

- (0 x 25.5)^½]

From the solubility data, it is independently known that γ₁₂ = 35.75 mJ/m², so this allows solving for the value of γ_PCB_ (= 3.5 mJ/m²). The following Table IV lists values of γ_PCS- for different values of the solubility.

For a smaller value of Sc (0.6 nm²), and S = 1 ppm, then γ₁₂ = 43.1 and γ_PCB- = 1.3 mJ/m².

Thus, the best estimate for the surface tension components of Aroclor 1248 from a combination of contact angle measurements and solubility is given in Table V, below.

III. Determination of the Interfacial Tension between Contaminant and Surfactant and the Criteria for Surfactant Selection.

The next part of the method of the invention is to determine the interfacial energy of the surfactant and the pollutant of interest. The interfacial tension between two liquids is measured by a variety of approaches, such as hanging drop, spinning drop, and drop weight method. By making use of γ₁₂ = [(γ₁ ^LW)^½ - (γ₂ ^L _W)^½]² + 2[(γ₁ ⁺ γ₁- ) ^½ +

(γ₂ ⁺ γ₂- ) ^½ - (γ₁ ⁺ γ₂- ) ^½ + (γ₁- γ₂+) ^½ ) (16) one can obtain y₁ ^LW, γ₁ ⁺, and γ₁- once the interfacial tension γ₁₂ between this liquid and three other completely characterized liquids are known.

Surfactant polar (γ⁺ and γ-) and non-polar (γ^LW ) surface tension components are then listed based upon chemical structure. This methodology, shown below, reveals the three surface tension components required for both the polar (hydrophilic) and the non-polar (lipophilic) parts of the surfactant molecule. Thus, if the surface tension values for N polar groups and M non-polar groups are known, then estimates for N*M surfactant combinations can be made. This gives one the ability to fine-tune surface tension requirements and to design surfactants for contaminant removal. =======================================================================================

One Surfactant HYDROPHILE - LIPOPHILE

Hydrophilic Group + Lipophilic Group

And six surface tension measurements:

three for: (Y_H ^LW _, γ_H ⁺, γ_H-) and

three for: ( γ_L ^LW , γ_L+, γ_L-) Gives

(γ_H-L ^LW, γ_H-L+, γ_L-L -) for the surfactant.

==============================================================================

The ΔG_p/m ^TOT between the contaminant, or pollutant (p), and soil, or mineral (m), is computed from Eqn. (7) or each combination. The ΔG_S/P ^TOT between the surfactant (s) and pollutant can also be determined. When

ΔG_S/P TOT > ΔG_p/m TOT, then the contaminant prefers to stick to the surfactant rather than the soil. Additionally, surfactants selected should hold to the criteria

ΔG_s/p ^TOT > ΔG_S/m ^TOT so that the surfactant will not preferentially stick to the soil, thus interfering in the extraction process.

A. Example for Interfacial Measurements.

The relevant surface tension values for water are: γ

= 72.8, γ^LW = 21.8, γ⁺ = 25.5, and γ- = 25.5 mJ/m² and for hexane are: γ = 18.4, γ₁₂ = 18.4, γ⁺ = 0, and γ- = 0. The values for quartz are: γ^LW = 39.9, γ⁺ = 0, and γ- = 25 mJ/m². The values for Aroclor 1248 are given in Table V above . The interfacial tension is given from Eqn . ( 16 ) above by: γ₁₂ = [(γ_pcb ^LW )^½ - (γ_water ^LW)^½]² + 2[(γ_pcb+ γ_pcb -)½

⁺ ( γ_water ⁺ γ_water )½ - ( γ_pcb + γ_water-)½ + ( γ _pcb- γ_water+)^½ ]²

The Dupre equation gives the free energy of adhesion:

ΔG₁₃₂ = γ₁₂ - γ₁₃ - γ₂₃ . Table VI below sets forth the adhesion energy of

Aroclor 1248 to quartz in the presence of (a) water and (b) hexane.

In Table VI, one can see that there is a substantial adhesion energy between the Aroclor 1248 and quartz, a common constituent in soils, in the presence of water. If the water were replaced by hexane, the adhesion energy is substantially reduced, but is still negative, which means that the Aroclor will still bind to the quartz.

Performing the same type of calculations with a suitable surfactant would reveal whether that surfactant created a positive adhesion energy, by which would mean that the Aroclor (or contaminant) would no longer bind to the quartz. That surfactant could then be useful in treating a soil polluted with the contaminant.

IV. Improvement of Surfactant Action by the Addition of a Co-Surfactant.

Subsequent to characterization of the polar and non- polar contributions to interfacial tensions in the soil- contaminant system, it is possible to improve the adhesion between surfactant and pollutant by seeding the soil with an oil-soluble co-surfactant.

The surface tension components which have been determined by contact angle measurements give parameters for the co-surfactant. For example, if the contaminant is largely apolar, (large γ- component), then a desirable combination of surfactant and oil-soluble co-surfactant would be a surfactant which is largely basic in nature and a co-surfactant which is largely acidic in nature. In order to have effective removal, the surfactant-co-surfactant pair must be chosen in such a way that the soil-contaminant contact angle goes to 180° when the surfactant solution is added to the contaminant soil, thus lifting the contaminant off the soil completely. The co-surfactant provides an additional set of parameters whereby this might be accomplished.

INDUSTRIAL APPLICABILITY

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

Claims

CLAIMS What Is Claimed Is:

1. A method for selecting a surfactant for the extraction of chemical pollutants from soils having at least one mineral component comprising:

(a) characterizing the soil;

(b) determining the surface energies of the pollutant and the soil; and

(c) estimating the chemical nature of the surfactant which would provide removal from the soil.

2. The method of Claim 1 wherein said soil is characterized 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, γ^LW , a second surface suitable for providing a measure of the polar, Lewis acid component of surface tension, γ⁺, and a third surface suitable for providing a measure of the polar, Lewis base component of surface tension, γ-, 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 extraction of chemical pollutants from soils having at least one mineral component comprising:

(1) characterizing the soil,

(2) determining the surface energies of the pollutant and the soil, and

( 3 ) estimating the chemical nature of the surfactant which would provide removal from the soil; and

(b) treating said contaminated soil with said at least one surfactant.

7. The method of Claim 6 wherein said soil is characterized 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 polar, 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 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.