Interlayer Cation Polarizability Affects Supercritical Carbon Dioxide Adsorption by Swelling Clays

Abstract

Several strategies for mitigating the build-up of atmospheric carbon dioxide (CO 2 ) bring wet supercritical CO 2 (scCO 2 ) in contact with phyllosilicates such as illites and smectites. While some work has examined the role of the charge-balancing cation and smectite framework features on CO 2 /smectite interactions, to our knowledge no one has examined how the polarizability of the charge-balancing cation influences these behaviors. In this paper, the scCO 2 adsorption properties of Pb 2+ , Rb + , and NH 4 + saturated smectite clays at variable relative humidity are studied by integrating in situ high-pressure X-ray diffraction (XRD), infrared spectroscopic titrations, and magic angle spinning nuclear magnetic resonance (MAS NMR) methods. The results are combined with previously published data for Na + , Cs + , and Ca 2+ saturated versions of the same smectites to isolate the roles of the charge-balancing cations and perform two independent tests of the role of charge-balancing cation polarizability in determining the interlayer fluid properties and smectite expansion. Independent correlations developed for (i) San Bernardino hectorite (SHCa-1) and (ii) Wyoming montmorillonite (SWy-2) both show that cation polarizability is important in predicting the interlayer composition (mol% CO 2 in the interlayer fluid and CO 2 /cation ratio in interlayer) and the expansion behavior for smectites in contact with wet and dry scCO 2 . In particular, this study shows that the charge-balancing cation polarizability is the most important cation-associated parameter in determining the expansion of the trioctahedral smectite, hectorite, when in contact with dry scCO 2 . While both independent tests show that cation polarizability is an important factor in smectite-scCO 2 systems, the correlations for hectorite are different from those determined for montmorillonite. The root of these differences is likely associated with the roles of the smectite framework on adsorption, warranting follow-up studies with a larger number of unique smectite frameworks. Overall, the results show that the polarizability of the charge-balancing cation should be considered when preparing smectite clays (or industrial processes involving smectites) to capture CO 2 and in predicting the behavior of caprocks over time.

Intercalation of CO2 Selected by Type of Interlayer Cation in Dried Synthetic Hectorite

“…For the works where MMT or other smectites have been studied, the clay–cation interaction is significantly different due to composition, charge density, charge homogeneity, and charge location within the layers. Such differences have been observed when examining SWy-2 and San Bernandino hectorite (SHCa-1), where correlations with the influence of cation polarizability on the CO 2 adsorption were different between the two . Comparing our results on fully fluorinated Hec with those of other natural Hec’s, where there is a compositional difference due to a varying degree of F – and OH – substitutions, we would expect a higher CO 2 adsorption in the present case from simulations, which is not the case.…”

“…Such differences have been observed when examining SWy-2 and San Bernandino hectorite (SHCa-1), where correlations with the influence of cation polarizability on the CO 2 adsorption were different between the two. 57 Comparing our results on fully fluorinated Hec with those of other natural Hec's, where there is a compositional difference due to a varying degree of F − and OH − substitutions, we would expect a higher CO 2 adsorption in the present case from simulations, 10 which is not the case. Third, for natural clays, side phases may significantly influence the uptake, for example, for Ni-Hec, where nickel hydroxide interstratified in the interlayer plays a dominant role in CO 2 adsorption.…”

Chemistry and Dynamics of Supercritical Carbon Dioxide and Methane in the Slit Pores of Layered Silicates

“…S.BowersG. M. Cunniff, S. S. Schaef, H. T. Burton, S. D. Walter, E. D. Hoyt, D. W. Loring, J. S. Bowers, G. M. 10.1021/acs.langmuir.2c021392022381554015551 …”

“…The intercalation of H 2 O in smectite interlayers can increase the gallery height, but in 2010, little data were available regarding smectite expansion in variably wet scCO 2 . Just after the first high-pressure XRD studies of forsterite and brucite carbonation were published by PNNL, Giesting et al used their own high-pressure XRD cell to examine montmorillonite expansion by CO 2 as a function of pressure, H 2 O content, and interlayer cation. , That same year, the first studies of smectite expansion using the PNNL high-pressure XRD and IR were published, followed by a number of papers in subsequent years describing expansion and interlayer pore fluid composition in the smectites montmorillonite and hectorite using the full PNNL high-pressure instrumentation suite. ,− These and other pioneering IR work show that the extent to which CO 2 enters and expands smectite interlayers is dependent on the fluid humidity, the charge-balancing cation properties, and the framework properties. Reported CO 2 uptakes range from 0 to 6 CO 2 /unit cell in a nominally dry smectite and 0 to 2 CO 2 /unit cell in wet smectites with ∼5 Å gallery heights.…”

Dissolution of Forsterite Surface in Brine at CO2 Geo-storage Conditions: Insights from Molecular Dynamic Simulations

“…And the interactions between properly dissolved cations and carbonyl groups are capable of improving the broken process of H−O bonds. For transport properties, Cunniff et al 11 reported that cation polarizability heavily influences the CO 2 concentration and cation/CO 2 ratio in the interlay fluid between smectite slabs. Zhou et al 12 studied the effect of moisture on CO 2 sequestration in kerogen slit pores.…”