The Spontaneous Alteration of Hydrogen Clay

Abstract--Di-ethyl 2-hexylphosphoric acid (di-2 EHPA) was chemisorbed on kaolinite and smectite in decane solution. The resultant isotherms were of the Langmuir type and made possible the determination of limiting adsorption values of 12 mg/g and 23.8 mg/g on H+-kaolinite and H+-montmor/llonite, respectively. The acidic phosphoric group of the di-2 EHPA molecule reacted in the anionic form (RO)~PO2-with the surface cations of the clay structures. Theoretical calculations, based on structural considerations, are in agreement with the experimental data and show that adsorption took place at the rate of one alkylphosphate anion per surface cation if the phyllosilicate was dioctahedral (e.g., montmorillonite and kaolinite). If the phyllosilicate was tdoctahedral (e.g., hectorite), adsorption took place at the rate of two di-2 EHPA molecules for three surface cations. Spectroscopic investigations performed with visible, ultraviolet, and infrared radiation confirmed the formation of salts or surface complexes.

Section: Methodsmentioning

confidence: 96%

Adsorption of Alkylphosphoric Acid on Kaolinite and Smectite in an Organic Medium (Decane)

Siffert¹

1981

“…Copyright 9 1990, The Clay Minerals Society Eeckman and Laudelout, 1960;Coleman and Craig, 1961;Miller, 1965) and that, because of hydrolysis, this displacement can occur when the electrolyte concentration is low, even if the montmorillonite is initially Na-saturated (Kamil and Shainberg, 1968;Shainberg, 1973;Shainberg et al, 1974;Frenkel and Suarez, 1977). The possibility exists, therefore, that changes in rheological properties with electrolyte concentration at low electrolyte concentrations are related to the displacement ofoctahedral AP + and Mg 2+ from the montmorillonite crystal.…”

Section: Introductionmentioning

confidence: 99%

Rheological Behavior of Na-Montmorillonite Suspensions at Low Electrolyte Concentration

Chen

Cushman

Low

1990

Abstract--The prevailing concept that positive-edge to negative-face attraction accounts for the rheological behavior of montmoriUonite suspensions at low electrolyte concentration was investigated. In one experiment, Mg 2+ released from Na-montmorillonite was measured at several NaC1 concentrations; in a second experiment, the viscosity, n, and the extrapolated shear stress, 0, were measured at several clay concentrations, pHs, and NaC! concentrations; and in a third experiment, the absorbance, A, was measured at two wavelengths (450 and 760 nm) at different clay and electrolyte concentrations. The released Mg 2+ decreased with increasing NaC1 concentration until it became zero at a NaC1 concentration between 0.01 and 0.02 M, depending on pH. Thereafter, it increased with increasing NaC1 concentration. Both 0 and n were highly correlated with the amount of released Mg 2+. Also, A remained constant until the NaC1 concentration corresponded to that at the minimum of 0. Thereafter, it increased and became linearly related to 0. These results suggest: (1) positive-edge to negative-face interaction cannot solely account for the rheological properties of montmorillonite at low electrolyte concentration, and (2) the release of octahedral Mg 2+ from montmorillonite affects 0, because it reduces the negative charge on the particles and, thereby, the repulsive force between them.

“…The quantity of base required to reach the potentiometric endpoints decreased in the following order: AN > H20 -DMF. Titration curves in H/O contained two inflection points, which are characteristic of (H+-Ala+)-saturated montmorillonite (Low, 1955;Barshad, 1960;Coleman and Craig, 1961;and Davis et al, 1962). The curves obtained by titration in DMF yielded two endpoints, which are also attributed to H § and AP +.…”

Section: Resultsmentioning

confidence: 95%

“…Potentiometric and conductometric titrations with a variety of bases have been used to differentiate H + from A13 § at the clay surface (Low, 1955;Barshad, 1960;Coleman and Craig, 1961;Davis et al, 1962;Shainberg and Dawson, 1967;Rich, 1970). Several researchers have used organic solvents for titrations of clay minerals.…”

Section: Introductionmentioning

confidence: 99%

Acidic Properties of Montmorillonite in Selected Solvents

Loeppert

Zelazny

Volk

1986

Abstract--Montmorillonites saturated with A1 a+, H+-A1 a+, and K + were titrated in H20, acetonitrile (AN), and dimethylformamide (DMF) to investigate the acidic properties of the clay in these solvents and to evaluate the application of nonaqueous titration procedures for studies of the acidic properties of 2:1 swelling clays. Samples were titrated with tetramethylammonium hydroxide using a combination glass electrode for potentiometric determination. Titers of base required to reach the final potentiometric endpoints were greater in AN than in DMF and H20. The larger titers in AN compared to H20 were attributed to pH-dependent sites for which an inflection was not observed in the latter solvent. Titration curves of Al-saturated montmorillonite in AN showed evidence of a salt-induced hydrolysis which was confirmed by titration curves of salt extracts. The hydrolysis reaction was more evident in AN than in H20 and was probably due to a disruption of the H20 structure by AN and a polarization of the H20 of solvation. The hydrolysis reaction was enhanced in the presence of excess salt due to the ion exchange of H § from the exchange surface. These studies indicate that acidic properties of clays may be drastically altered in organic solvents. The acidic properties may be used to advantage, for example, in the determination of edge-site acidity. In addition, they have implications concerning possible chemical reactions and/or alterations of clay in organic solvents.