Interfacial interactions of homoionic montmorillonites with water and electrolytes studied by Fourier transform infrared spectroscopy and microcalorimetry

Laibin Yan, Purdue University

Abstract

This thesis reports the results of four different investigations in chapters entitled (1) enthalpy changes produced by layer collapse and interlayer ion penetration in homoionic montmorillonites; (2) relation between the swelling pressure of montmorillonite layers and H-O-H bending frequency in the interlayer water; (3) changes in the Si-O vibrations of smectite layers accompanying the sorption of interlayer water; (4) effects of monovalent, exchangeable cations and electrolytes on the infrared vibrations of smectite layers and interlayer water. The enthalpy changes, $\Delta H$, in suspensions of Li-, Na-, and K-montmorillonite with LiCl, NaCl and KCl solutions, the swelling pressure, $\Pi$, the four Si-O stretching vibrations, $\nu\sb{\rm Si-O}$, of montmorillonite layers and the bending vibrations, $\nu\sb2$, of the interlayer water were measured by means of a differential Calvet microcalorimeter, a miniature pressure membrane apparatus, and ATR-FTIR spectrophotometer, respectively. The values of $\Delta H$ were compared with the corresponding changes in interlayer distance, $\lambda$, as determined by X-ray diffraction. It was found the heat of flocculation is negligible, and that the value of $\Delta H$ was positive for Li-montmorillonite, but negative for Na- and K-montmorillonite. These observations were interpreted to mean that $\Delta H$ changes in the montmorillonite suspension were largely attributable to the penetration of electrolyte into the interlayer space and reorganization of the interlayer space by the added electrolytes. Oriented gels of Li- and Na-montmorillonite equilibrated at different $m\sb{w}/m\sb{c}$, the mass ratio of water to clay, and $\Pi$, were obtained by using a pressure membrane apparatus. One part of each gel was used for the gravimetric determination of $m\sb{w}/m\sb{c}$. The other part was transferred to an FTIR spectrometer where the spectrum of the gel was measured by attenuated total reflectance. Thus, the dependence of $\Pi$, $\nu\sb{\rm Si-O}$ and $\nu\sb2$ on $m\sb{w}/m\sb{c}$ was determined in the same samples. It was found that $\Pi$ and $\nu\sb2$ were both exponential functions of $m\sb{c}/m\sb{w}$ and a linear relation exited between ln($\Pi$ + 1) and ln($\nu\sb2/\nu\sb2\sp\circ$), where $\nu\sb2\sp\circ$ is the H-O-H bending frequency of bulk water. $\nu\sb{\rm Si-O}$ in montmorillonite was found to change over a very wide range of $m\sb{w}/m\sb{c}$, and a linear relation existed between ln($\nu\sb{\rm Si-O}$) and ln($\nu\sb2$). These results were interpreted to mean that the Si-O stretching vibrations in the montmorillonite layers and H-O-H bending vibrations in the interlayer water are coupled and that both change as the layers come closer together. This vibrational coupling was essentially independent of Na$\sp+$ or Li$\sp+$ as the exchangeable cation and C, the concentration of electrolyte solutions. C has little or no effect on the relation between $\nu\sb{\rm Si-O}$ and $m\sb{w}/m\sb{c}$, or on the relation between $\nu\sb2$ and $m\sb{w}/m\sb{c}$. Thus, neither Na$\sp+$ or Li$\sp+$ as the exchangeable cation nor C had any specific effects on the structure of the clay layers or the structure of the interlayer water.

Degree

Ph.D.

Advisors

Roth, Purdue University.

Subject Area

Chemistry|Agronomy|Environmental science

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