Exchange Reactions in the Ca-Mg-Na-Montmorillonite System

Abstract

Abstract--The exchange reactions of Na, Ca and Mg on montmorillonite are revisited employing recently developed analytical and theoretical approaches. The fractional adsorption of the cations has been determined by displacing them from the adsorbed state in one step, using a low concentration of an organic cation of large binding affinity. The analysis of displaced and solution cations employed inductively coupled plasma emission spectrometry. An adsorption model was employed in the analysis of the data. The procedure consists of solving the electrostatic Gouy-Chapman equations and calculating adsorbed amounts of the cations as the sum of the cations residing in the double layer region, and the cations chemically bound to the surface, in a closed system. The model also accounts explicitly for cation complexation in solution. Thus the calculations also considered the adsorption of CaC1 + and MgCI +, which eliminated the apparent increase of the cation exchange capacity (CEC) with divalent cation concentration. The model could explain and yield predictions for our measured adsorbed amounts as well as previously published data, in the binary and ternary systems of Ca/Mg/Na, provided that the fraction of surface sites occupied by calcium did not exceed 0.4. For a larger coverage of surface sites by calcium, a fit of the experimental data required an order of magnitude increase in the binding coefficients of the divalent cations in the binary system Ca/Na and in the ternary system Ca/Mg/Na.

Modeling Adsorption-Desorption Processes of Cd on Montmorillonite

“…The results were analyzed with the adsorption model (Nir 1986;Nir et al 1986;Hirsch et al 1989;Rytwo et al 1996) by using binding coefficients from previous studies (given in Table 1). The calculations con- (Rytwo et al 1996 and the current work); Cd (10 M -l) and CdCI + (30 M -I) as in Hirsch et al (1989); Na (0.5 M-~), K (4 M 1) as in Nir et al (1986).…”

“…The calculations con- (Rytwo et al 1996 and the current work); Cd (10 M -l) and CdCI + (30 M -I) as in Hirsch et al (1989); Na (0.5 M-~), K (4 M 1) as in Nir et al (1986). The total concentrations in the system (clay + solution) were 2.52 mM for Ca, 0.479 mM for Mg, 0.048 mM for K and 10.13 mM for Na.…”

High Resolution Gas Adsorption Study on Montmorillonite Clays from Côte d’Ivoire: Assessment of Surface Energetic Properties

“…This process was repeated three times. The cation-saturated montmorillonite was then washed three or four times with distilled water until the AgNO 3 test for chloride became negative [18,19].…”

The influence of potassium on the weathering properties of kimberlite and the information provided by different testing methods

“…It has been shown that kimberlite is prone to weathering when smectite minerals are present [2] and that weathering correlates with the abundance of smectite. Cation exchange takes place in smectites and changes the mechanical properties of the kimberlite [3], [4], [5] and [6]. K + is one of the few cations that collapse the swelling clay interlayer of smectites [7], [8] and [9].…”