Colloidal agents for aquifer remediation

Abstract

Compositions and methods for treating contaminated soil and/or ground water in situ. The compositions and methods comprise stabilized forms of colloidal activated carbon that are used to quickly sorb contaminants. Unlike traditional activated carbon in granular or powder form, the compounds and methods of the present invention are operative to transport particulate activated carbon through a matrix of soil and groundwater upon application by injection, gravity feed, or percolation into soil and groundwater, which in turn decontaminate groundwater in place without the cost or disruption associated with digging the contaminated soil and groundwater out of the ground for on-site purification or disposal at a hazardous waste landfill.

Claims

1. A composition for use in aquifer remediation, said composition consisting essentially of: particulate activated carbon; a stabilizing polymer; a distribution enhancement agent chosen from an anionic surfactant, nonionic surfactant, chelating agent, or combinations thereof, any chelating agents chosen being from the group consisting of: citrates, phosphates, silicates, borates, sulfates, carbonates, aminocarboxylic acids and salts thereof, polyamines, and combinations thereof; and wherein said particulate activated carbon:stabilizing polymer:distribution enhancement agent are present in amounts relative one another by weight in a ratio in a range of 1:0.01-1.0:0.01-1.0.

2. The composition of claim 1 wherein said relative amounts of particulate carbon:stabilizing polymer:distribution enhancement agent are present in a ratio in a range of 1:0.05-0.5:0.025-0.5.

3. The composition of claim 1 wherein said stabilizing polymer is selected from the group consisting of an anionic polymer and a nonionic polymer.

4. The composition of claim 3 wherein said stabilizing polymer is selected from the group consisting of carboxymethyl cellulose, carrageenan, polyacrylate, xanthan gum, and combinations thereof.

5. The composition of claim 1 wherein said nonionic surfactants of said distribution enhancement agent is selected from the group consisting of alkyl polyethylene oxides, ethylene oxide polymers, polyethylene oxide lauryl ether, ethylene oxide-propylene oxide copolymers and combinations thereof.

6. The composition of claim 1 wherein said particulate activated carbon has a particle size ranging from 0.1 to 10 microns.

7. An aqueous admixture for removing contaminants from an aquifer consisting essentially of: particulate activated carbon; a stabilizing polymer; a distribution enhancement agent chosen from an anionic surfactant, nonionic surfactant, chelating agent, or combinations thereof, any chelating agents chosen being from the group consisting of: citrates, phosphates, silicates, borates, sulfates, carbonates, aminocarboxylic acids and salts thereof, polyamines, and combinations thereof; and wherein said ratio of said particulate activated carbon:stabilizing polymer:distribution enhancement agent are present in amounts relative one another by weight in a range of 1:0.01-1.0:0.01-1.0; water; and wherein said water, particulate activated carbon, stabilizing polymer and distribution enhancement agent are operative to form a colloid wherein said particulate carbon is present in an amount ranging from 0.01% to 70.0% by weight in said water.

8. The aqueous admixture of claim 7 wherein said particulate carbon is present in an amount ranging from 0.05% to 40.0% by weight in said water.

9. The aqueous admixture of claim 7 wherein said particulate carbon is present in an amount ranging from 0.1% to 20.0% by weight in water.

10. The aqueous admixture of claim 7 wherein said particulate activated carbon has a particle size ranging from 0.1 to 10 microns.

11. A method of capturing or immobilizing contaminants from soil and groundwater comprising the steps: a) forming an aqueous admixture, said aqueous admixture consisting essentially of: particulate activated carbon; a stabilizing polymer; a distribution enhancement agent chosen from an anionic surfactant, nonionic surfactant, chelating agent, or combinations thereof, any chelating agents chosen being from the group consisting of: citrates, phosphates, silicates, borates, sulfates, carbonates, aminocarboxylic acids and salts thereof, polyamines, and combinations thereof; and wherein said ratio of said particulate activated carbon:stabilizing polymer:distribution enhancement agent are present in amounts relative one another by weight in a range of 1:0.01-1.0:0.01-1.0; and water; wherein said particulate carbon is present in an amount ranging from 0.01% to 70% by weight in said water; and b) applying said aqueous admixture formed in step a) to said soil and groundwater such that said admixture becomes distributed and dispersed within said soil and groundwater.

12. The method of claim 11 wherein in step b), said aqueous admixture is applied by injection into said soil and groundwater.

13. The method of claim 12 wherein said injection comprises high pressure injection or fracturing.

14. The method of claim 11 wherein step b) said aqueous admixture is applied by gravity feed to said soil and groundwater.

15. The method of claim 11 wherein step b) said aqueous admixture is applied by percolation.

16. The method of claim 11 wherein in step a), said particulate activated carbon has a particle size ranging from 0.1 to 10 microns.

Description

DETAILED DESCRIPTION

(1) The detailed description set forth below is intended as a description of the presently preferred embodiment of the invention, and is not intended to represent the only form in which the present invention may be implemented or performed. The description sets forth the functions and sequences of steps for practicing the invention. It is to be understood, however, that the same or equivalent functions and sequences may be accomplished by different embodiments and that they are also intended to be encompassed within the scope of the invention.

(2) New compositions and methods have been developed that enable increased distribution of activated carbon colloids through soil and groundwater. This allows for very cost-effective treatment of contaminated aquifers, and therefore control over mobility of contaminants in groundwater and soil systems.

(3) The present invention is a mixture of very fine activated carbon (0.1 to 10 micron size, and preferably within a 0.5 to 2 micron range) stabilized by at least two additives, wherein the first additive is a stabilizing polymer, and the second additive is a distribution enhancement agent. The addition of one or more distribution enhancement agents enables the colloidal material to distribute significantly further through soil and groundwater during application than the compositions and methods of the prior art.

(4) The first additive, or stabilizing polymer, can be an anionic polymer or a nonionic polymer. Examples include but are not limited to carboxymethyl cellulose (CMC), carrageenan, polyacrylic acid, xanthan gum (nonionic), and combinations thereof.

(5) The second additive, or distribution enhancement agent, is selected from the following list: chelating agents, anionic polymers, anionic surfactants, or nonionic surfactants, and possible combinations thereof.

(6) Chelating agents include but are not limited to citrates, phosphates (e.g. SHMP, STTP, TSPP), silicates, borates, sulfates, carbonates, aminocarboxylic acids and salts thereof (e.g. EDTA, MGDA and NTA), polyamines such as ethylene diamine, as well as combinations thereof.

(7) Anionic polymers of the second additive include but are not limited to sulfated or carboxylated polysaccharides, polyacrylates, polyacrylamides, lignosulfonate, polyacrylate copolymers, and combinations thereof.

(8) Anionic surfactants include but are not limited to dioctyl sodium sulfosuccinate, alkyl and aryl sulfates (e.g. sodium lauryl sulfate), alkyl carboxylates (e.g. sodium laurate) and combinations thereof.

(9) Nonionic surfactants include but are not limited to alkyl polyethylene oxides, ethylene oxide polymers, polyethylene oxide lauryl ether (e.g., Brij 30® produced by Croda, Inc.), ethylene oxide-propylene oxide copolymers (e.g., Tergitol XD® produced by the Dow Chemical Company), and combinations thereof.

(10) Compositions of this invention are preferably formed wherein the relative weight ratios of carbon:first additive (stabilizing polymer):second additive (distribution enhancing agent) are in the range of: 1:0.01-1.0:0.01-1.0 and preferably in the ranges of 1:0.05-0.5:0.025-0.5

(11) The method of groundwater treatment using this invention includes injection or other application of the above compositions as a water-based colloid such that the activated carbon concentration between 0.01% and 70.0% by weight in water. Preferably, the material can be injected in the range of 0.05% to 40.0% activated carbon by weight in water. Even more preferably, it can be injected in the range of 0.1% to 20.0% carbon by weight in water. In addition to injection, such as high pressure injection and fracturing, the aqueous admixture containing the compositions of the present invention can be applied by gravity feed or percolation in the amount sufficient to adsorb the contaminants believed to be present in a given area of contaminated soil/groundwater. Along those lines, depending on the site geology and degree of contamination, a general application rate can range from between approximately 1 to 80 gallons of the aqueous admixture of the water-based colloid of the present invention per cubic yard of soil and groundwater to be treated, and preferably between approximately 4 and 60 gallons of the aqueous admixture per cubic yard treated.

(12) By way of illustration, and by no means as limiting the present invention, the following examples are provided: Example 1: Dispersion preparation: A series of colloidal dispersions were prepared with the following general composition: 1% w/w activated carbon (approximately 1.5 micron average particle size), 0.25% w/w stabilizing polymer, and 0.25% w/w distribution enhancement agent. The dispersions were prepared as follows: The stabilizing polymer and second additive were mixed thoroughly into water with a high-shear mixer and mixed until homogeneous. A slurry of activated carbon in water was then added to the mixture. Each dispersion was mixed for an additional 5 minutes resulting in a very homogeneous, black colloidal suspension. The compositions of the tested dispersions and some comparative samples are shown in Table 1.

(13) Example 2: Column transport testing: Each of the colloids in Example 1 was diluted with tap water to a carbon concentration of 2,000 mg/L. A 25 g aliquot of each diluted colloid was eluted through a glass column (bed dimensions 2.5×24.0 cm) packed with saturated soil having a sand/silt/clay ratio of 93.7/3.9/2.4. The 25 g sample was eluted through the column and flushed with additional tap water until the column effluent was clear. Activated carbon in the combined effluent from each column study was measured by UV-visible spectroscopy. The total mass of carbon eluted was calculated using a calibration curve. For comparison to the prior art, a standard colloid sample stabilized only by CMC was studied (Sample #1). The mass of carbon eluted by each sample is reported in table 1, and the amount of carbon eluted is also reported as a percentage relative to the standard.

(14) The data in Table 1 show that the present invention results in significant increases of activated carbon colloid transport through soil and groundwater. It is also apparent from these data that the use of the stabilizing polymer or distribution enhancement agents alone results in very poor performance, and therefore their combination is required. This invention provides a significant improvement in efficiency and reduction in cost for treatment of contaminated aquifers.

(15) TABLE-US-00001 TABLE 1 Composition and Column Study Data mg Carbon Sample Stabilizing Distribution Carbon Eluted vs Number Polymer Enhancer Eluted Standard 1 CMC (standard) None 5.4 100% 2 CMC MGDA 17.3 320% 3 CMC ethylene oxide/propylene 21.1 391% oxide copolymer (Tergitol XD ®) 4 CMC EDTA 14.1 261% 5 CMC Sodium citrate 18.2 337% 6 CMC NTA 20.5 380% 7 CMC SHMP 14.7 272% 8 CMC STPP 20.0 370% 9 CMC Lignosulfonate 21.1 391% 10 CMC polyethylene oxide 20.2 374% lauryl ether (Brij 30 ®) 11 CMC SLS 22.4 415% 12 CMC Sodium laurate 24.5 454% 13 CMC DSS 15.7 291% 14 CMC TSPP 16.0 296% 15 CMC SDBS 22.8 422% 16 Carrageenan None 5.1  94% 17 Carrageenan SHMP 11.5 213% 18 Xanthan Gum* None 7.5 139% 19 Xanthan Gum* STPP 16.1 298% 20 None MGDA 0  0% 21 None polyethylene oxide lauryl 0  0% ether (Brij 30 ®) 22 None ethylene oxide/propylene 0  0% oxide copolymer (Tergitl XD ®) 23 None None 0  0%

(16) Xanthan gum experiments were run on shorter columns and therefore not directly comparable

(17) Abbreviations as utilized and referenced in the specification:

(18) CMC carboxymethyl cellulose, sodium salt

(19) DSS dioctyl sodium sulfosuccinate

(20) EDTA ethylenediaminetetraacetic acid, sodium salt

(21) MGDA methylglycine diacetic acid, sodium salt

(22) NTA nitrilotriacetic acid, sodium salt

(23) SDBS sodium dodecylbenzenesulfonate

(24) SHMP sodium hexametaphosphate

(25) SLS sodium lauryl sulfate

(26) STPP sodium tripolyphosphate

(27) TSPP tetrasodium pyrophosphate

(28) Additional modifications and improvements of the present invention may also be apparent to those of ordinary skill in the art. Thus, the particular combination of parts and steps described and illustrated herein is intended to represent only certain embodiments of the present invention, and is not intended to serve as limitations of alternative devices and methods within the spirit and scope of the invention.