Effect of Surfactant on the Index Properties of Clayey Soils Contaminated with Naphthalene
Junboum Park* and C. Vipulanandan**
*Department of Civil Engineering, Seoul National University, Seoul, Korea 151-742
Phone: +82-2-880-8356(O); e-mail: junbpark@gong.snu.ac.kr
**Department of Civil & Environmental Engineering, University of Houston, Houston, TX, 77204-4791
Phone: (713) 743-4278; e-mail: cvipulanandan@uh.eduAbstract
Effect of adding surfactants to naphthalene contaminated kaolinite and bentonite was investigated. All of the surfactants at 10 CMC decreased the surface tension of water less than 35 dynes/cm. Biosurfactant was basic (pH=10.5) at 10 CMC. Biosurfactant at 10 g/L (pH=10.5) increased the solubility of naphthalene from 32 mg/L to 600 mg/L. SDS (anionic) surfactant substantially decreased the plasticity indices from 18 to 7, and from 386 to 288 for kaolinite and bentonite clays, respectively. Whereas, the biosurfactant and Triton X-100 (nonionic) surfactant did not affect the plasticity of the test soils. The effect of naphthalene on the index properties was negligible.
Introduction
Remediation of contaminated soils by soil flushing is one of the emerging and innovative techniques, specifically for the DNAPLs (Dense Non-Aqueous Phase Liquids) sorbed onto soil particles by physicochemical interactions. Surfactants can be properly used to enhance the desorption and solubilization of organic contaminants into water. However, surfactants may become sources of secondary contamination, and furthermore, they may also change the engineering properties of soils into undesirable state. This adverse effect should be carefully studied for the adequate application of soil flushing for the remediation of organic contaminated soils in situ.
Objectives and Testing Program
This paper focuses on the investigation of the change in the index properties of contaminated clayey soils due to the addition of surfactants. The interactions between clay-surfactant-naphthalene were studied with three types of surfactants. Atterberg limit tests were performed on kaolinite and bentonite clays before and after naphthalene contamination, with and without the addition of biosurfactant, SDS (anionic), and Triton X-100 (nonionic) surfactants at the concentration of 10 CMC. Surface tension and pH changes were also measured before and after the addition of surfactants. As a dispersing agent, NaPO3 was also tested and the changes in soil properties were compared with surfactants.
Results
Test results are summarized in Tables 1, 2, and 3.
Table 1. LL, PL, and PI Changes Before/After the Addition of Naphthalene into Kaolinite and Bentonite
DI Water
4% NaPO3
Biosurfactant
Triton X-100
SDS
LL(Kaolinite)
47(46)
28
47(46)
48(48)
30(32)
PL(Kaolinite)
29(28)
27
33(30)
31(24)
23(26)
PI(Kaolinite)
18(18)
0.3
15(15)
17(24)
7(5)
LL(Bentonite)
420(445)
241
403(405)
448(375)
338(360)
PL(Bentonite)
34(48)
47
43(100)
43(61)
50(75)
PI(Bentonite)
386(397)
193
359(305)
405(314)
288(285)
Numbers in ( ) were obtained with 32 mg/L of naphthalene solution at room temperature.
Table 2. Surface Tension Before/After the Addition of Naphthalene (Unit: dynes/cm)
DI Water
4% NaPO3
Biosurfactant
Triton X-!00
SDS
Before Naph. Addition
77
56
29
30
33
After Naph. Addition
76
51
31
32
35
Table 3. pH Changes Before/After the Addition of Naphthalene at Max. Solubility
DI Water
4% NaPO3
Biosurfactant
Triton X-100
SDS
Before Naph. Addition
7.7
6.7
10.5
8.0
8.5
After Naph. Addition
7.7
6.6
10.6
8.0
8.4
Conclusions
All of the surfactants at 10 CMC decreased the surface tension of water less than 35 dynes/cm. Biosurfactant was basic (pH=10.5) at 10 CMC.SDS substantially decreased the plasticity of both kaolinite and bentonite clays, as the dispersing agent reduced the plasticity of bentonite to approximately half of the value obtained with DI water (PI=386). The dispersing agent turned kaolinite into almost non-plastic soil (PI=0.3). Biosurfactant and Triton X-100 (nonionic) surfactant did not affect the plasticity of the test soils. The effect of naphthalene on the index properties was negligible.
Acknowledgement
This study was supported by funding from Advanced Technology Program of State of Texas and Texas Hazardous Waste Research Center (THWRC)
References
Mackay, D. M. and Cherry, J. A. (1989), "Ground Water Contamination: Pump-and-Treat Remediation," Environmental Science and Technology, Vol. 23, No. 6, pp. 630-636
Ren, X. (1998), Application of Biosurfactant in Naphthalene, Phenanthrene, and TCE Remediation, Ph. D. Dissertation, University of Houston, Houston, TX.
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