Role of cation size on swelling pressure and free energy of mica pores

Adapa, Sai; Malani, Ateeque

doi:10.1016/j.jcis.2021.04.034

Cited by 8 publications

(12 citation statements)

References 55 publications

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“…Further, the sharing analysis of hydration shell shows that out of which which holds the mica frameworks of opposite sides together by hydration bridge. Similar water bridge by direct hydration of ions located on opposite sides of pore were observed in K-mica system in our recent work 65 , and others too 56 . We also calculated of Na ions with both water oxygen and surface oxygens as shown in Figure 9 .…”

Section: Resultssupporting

confidence: 86%

“…The above analysis indicates that those ions which has higher size that snuggly fits and forms larger number of hydration with surface oxygens of mineral surface acts as anchor and holds the opposite side mineral surface by forming water bridge. Such scenario was observed in recent study of water adsorption in K-, Rb- and Cs-mica pres, as well 65 . With decrease in size of ion and increase in hydration energy, the interaction with mineral surface decreases and ion hydration is favored by free water molecules, therefore such ions favor swelling in mineral surfaces.…”

Section: Resultssupporting

confidence: 70%

“…While these studies investigated the structure of confined water and ions, clay-hydration energy in detail; however the individual pair interactions i.e., ion-surface, water-surface, and surface-surface interactions have not been investigated in details. Our recent study 65 and that of Shen and Bourg 63 , and Li et al 64 have probed these individual interactions and found a significant role in the swelling free energy of clays. In our recent work 65 , we probed the swelling behaviour of mica clay where interstitial cations (K , Rb , and Cs ions) were having similar hydration properties.…”

Section: Introductionmentioning

confidence: 78%

“…Our recent study 65 and that of Shen and Bourg 63 , and Li et al 64 have probed these individual interactions and found a significant role in the swelling free energy of clays. In our recent work 65 , we probed the swelling behaviour of mica clay where interstitial cations (K , Rb , and Cs ions) were having similar hydration properties. Our analysis found that even 0.1 Å difference in size of these cations leads to significant changes in swelling pressure, free energy and hence percentage of swellings.…”

Section: Introductionmentioning

confidence: 78%

“…We have used the previously developed computational procedure 52 , 65 ; hence, here we describe it in brief, and details are provided in supplementary information (SI). We created mica surface of dimesnions with naturally occuring -ions from the X-ray data 70 .…”

Section: Simulation Detailsmentioning

confidence: 99%

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Cation hydration by confined water and framework-atoms have crucial role on thermodynamics of clay swelling

Adapa

Malani

2022

Sci Rep

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The swelling capacity and stability of clay play a crucial role in various areas ranging from cosmetics to oil extraction; hence change in their swelling behaviour after cation exchange with the surrounding medium is important for their efficient utilisation. Here we focus on understanding the role of different hydration properties of cation on the thermodynamics of clay swelling by water adsorption. We have used mica as the reference clay, Na$$^+$$ + , Li$$^+$$ + , and H$$^+$$ + ions as the interstitial cations, and performed grand canonical Monte Carlo simulations of water adsorption in mica pores (of widths $$d = 4-40$$ d = 4 - 40 Å). The disjoining pressure ($$\Pi$$ Π ), swelling free energy ($$\Delta \Omega ^{ex}$$ Δ Ω ex ), and several structural properties of confined water and ions were calculated to perform a thermodynamic analysis of the system. We expected higher water density in H-mica pores ($$\rho_{ \hbox{H}}$$ ρ H ) due to the smaller size of $$\hbox {H}^+$$ H + ions having higher hydration energy. However, the counter-intuitive trend of $$\rho _{\hbox{Li}}> \rho _{\hbox{Na}} > \rho_b$$ ρ Li > ρ Na > ρ b (bulk density) $$> \rho_{\hbox{H}}$$ > ρ H was observed due to adsorption energy, where the interaction of water with mica framework atoms was also found to be significant. All three mica systems exhibited oscillatory behaviour in the $$\Pi$$ Π and $$\Delta \Omega ^{ex}$$ Δ Ω ex profiles, diminishing to zero for $$d \ge 11$$ d ≥ 11 Å. The $$\Delta \Omega ^{ex}$$ Δ Ω ex for Na-mica is characterised by global minima at $$d=6 {\hbox {\AA}}$$ d = 6 Å corresponding to crystalline swelling with significant and multiple barriers for crystalline swelling to osmotic swelling ($$d > 12$$ d > 12 Å). A shift in the location of global minima of $$\Delta \Omega ^{ex}$$ Δ Ω ex towards the higher d values and $$\Delta \Omega ^{ex}$$ Δ Ω ex becoming more repulsive is observed in the increasing order of hydration energy of $$\hbox {Na}^+$$ Na + , $$\hbox {Li}^+$$ Li + , and $$\hbox {H}^+$$ H + ions. The $$\Delta \Omega ^{ex} > 0$$ Δ Ω ex > 0 for all d in the H-mica system thus favours osmotic swelling. We found that the Na$$^+$$ + ions hydrate more surface oxygens, act as anchors, and hold the mica pore together (at smaller d), by sharing hydrating water with ions of the opposite side, forming an electrostatically connected mica-Na-water-Na-mica bridge. The Li$$^+$$ + ions do hydrate surface oxygen atoms, albeit in lesser numbers, and sharing of hydration shell with nearby Li$$^+$$ + ions is also minimum. Hydration by surface atoms and water sharing, both, are minimum in the H$$^+$$ + ion case, as they are mostly present in the center of the pore as diffusive ions, thus exerting a consistent osmotic pressure on the mica frameworks, favouring swelling.

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