Date on Master's Thesis/Doctoral Dissertation

8-2017

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Civil and Environmental Engineering

Degree Program

Civil Engineering, PhD

Committee Chair

Zhao, Qian

Committee Co-Chair (if applicable)

Rockaway, Thomas

Committee Member

Rockaway, Thomas

Committee Member

Kim, Young Hoon

Committee Member

Yang, Li

Author's Keywords

clay; organoclay; hydrocarbon sorption; microstructure; clay barrier; reactive geo-material

Abstract

This study focuses on the microstructure of organoclays after organic surfactant modifications and the potential use in geoenvironmental engineering applications including waste containment in earthen barrier, rheological control agents for drilling fluid and soil stabilization. Organoclays, or clays modified by organic matters, are often synthesized by exchanging the naturally occurring interlayer inorganic cations (e.g., Na+, Ca2+) of the clay with organic cationic surfactants. In this research, montmorillonites intercalated with two quaternary ammonium surfactants, hexadecyltrimethylammonium (HDTMA+) and bis (hydrogenated tallow alkyl) dimethyl ammonium were used as the representative organo-rich, partitioning clays. The laboratory characterization techniques including XRD, TEM and FT-IR were employed to examine the interactions between montmorillonite minerals, surfactants, and organic sorbates. The results of XRD and TEM showed the successive interlayer expansion of montmorillonite because of intercalation of surfactants and hydrocarbons sorbates. The FT-IR results further confirmed the arrangement of the intercalated surfactant and the organic sorbates due to primary and secondary sorption. To understand the engineering behaviors of organoclays in earthen barriers, the free swelling and hydraulic conductivity tests were conducted to evaluate the permeability of compacted clay and geosynthetic clay liner (GCL) amended with HDTMA-organoclay. The results suggested that the addition of organoclay (less than 10%) in compacted clay slightly increased the permeability of the mixture to water. However, due to the interaction between the organophilic phase in organoclays and non-polar liquids, low amounts of organoclay within the compacted clay admixture significantly decreased its permeability for non-polar liquids such as gasoline. Moreover, it was observed that low weight percentages of HDTMA-bentonite (up to 20% by weight) had little or no impact on the hydraulic conductivity of the Na-bentonite or Ca-bentonite GCL. However, higher dosages of organoclay in GCLs could reduce the permeability to organic fluids such as gasoline. The impact of the amount of organoclay additives, pressure and temperature on the rheological behavior of organoclay/oil-based drilling fluids was investigated. The obtained results from XRD test suggested that the oil molecules entered the PM199 interlayer, resulting in swelling and exfoliation of PM199. It was observed that the viscosity of 5% PM199 suspension slightly decreased by increasing the temperature from 25 to 60 °C, and then the viscosity increased when the temperature raised from 60 to 150 °C. Moreover, it was found that the viscosity of 5% PM199 suspension increased when the pressure increased from 0 to 200 bar due to physical changes on both oil and organoclay particles. The effectiveness of organoclay and Portland cement for the solidification and stabilization (S/S) of contaminated soils was investigated in the laboratory. The results indicated that the addition of cement (5% or 10% by weight) reduced the hydraulic conductivity and increased the compressive strength of the solidification and stabilization soil specimens. Additionally, the leaching test results indicated that the addition of organoclay during solidification and stabilization significantly reduced the leaching of naphthalene and phenanthrene from the stabilized soil specimen. The results suggested that organoclay particles sorbed the organic contaminates and consequently reduced the naphthalene and phenanthrene leachate concentration. Also, it was observed that the naphthalene and phenanthrene leachate concentration decreased by increasing the curing time of S/S products. Overall, this study performed laboratory tests to obtain information regarding the microsturcture of cationic surfactant modifed bentonties and their engineering behaviors (e.g. hydrophobicity, swelling, permeability, stability in oil suspension). The obtained results are expected to yield significant insights into their potential applications as sorbents in hydraulic and sorptive barriers for organic compounds; rheological control additives in oil-based drilling fluid; agents for stabilization and solidification of contaminated soils.

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