Montmorillonite modeling

Examines interfacial processes in a montmorillonite model system... 

For poly(propylene oxide) ammonium (PPO-NH3 )/Na -montmorillonite models, some Na cations were removed from the amine-based model, and some amine functional groups were protonated so as to maintain the electroneutrality of the whole system. 

Fig. 6. Pilot-scale kiln results for a fill fraction of 0.08% at 0.5 rpm and an initial toluene loading, on a dry, calcined, montmorillonite clay adsorbent, of 0.25 wt %, at A, 790°C B, 330°C and C, 190°C. The soHd lines are model fits using equation 24. The model simultaneously fits to all of the data (24).

In their model they used a kaolinite-like clay for the degraded silicate and allowed Na, Mg, and K to react to form sodic montmorillonite, chlorite, and illite respectively. The balance is essentially complete with only small residuals for H4Si04 and HCOT The newly formed clays would constitute about 7% of the total mass of sediments. 

Methyltins are less likely than the butyl- and octyl-tins to partition to sediments, soils, and organic carbon. Modelled data for K c suggest much lower capacity for binding to organic carbon than do measured values, often by several orders of magnitude. Measured data have been used in preference to model environmental fate of the compounds. The compounds also bind strongly to clay minerals, montmorillonite in particular. 

As noted above, adsorption isotherms are largely derived empirically and give no information on the types of adsorption that may be involved. Scrivner and colleagues39 have developed an adsorption model for montmorillonite clay that can predict the exchange of binary and ternary ions in solution (two and three ions in the chemical system). This model would be more relevant for modeling the behavior of heavy metals that actively participate in ion-exchange reactions than for organics, in which physical adsorption is more important. 

Why can layer silicates serve as models for replication processes The answer is simple they have properties which are observed in replicating systems. Montmorillonite crystals contain similar parallel layers, the distance between which... 

The first indication of a possible connection between geological processes occurring at the boundaries between tectonic plates of the mid-oceanic ridges and the biogenesis problem was provided by J. B. Corliss (1981). He considered the hydrothermal conditions to be ideal reactors for abiotic synthesis these ideal conditions were the water temperature gradients, the pH, and the concentrations of solutes in the hot springs. The presence of certain minerals which could act as catalysts, such as montmorillonite, clay minerals, iron oxide, sulphides etc., was also very important. The initial model presented for the hydrothermal synthesis of biomolecules (Corliss, 1981) was modified, particularly by Russell (1989) and Wachtershauser (see Sect. 7.3). 

A theoretical model for the adsorption of metals on to clay particles (<0.5 pm) of sodium montmorillonite, has been proposed, and experimental data on the adsorption of nickel and zinc have been discussed in terms of fitting the model and comparison with the Gouy-Chapman theory [10]. In clays, two processes occur. The first is a pH-independent process involving cation exchange in the interlayers and electrostatic interactions. The second is a pH-dependent process involving the formation of surface complexes. The data generally fitted the clay model and were seen as an extension to the Gouy-Chapman model from the surface reactivity to the interior of the hydrated clay particle. 

Montmorillonite catalysis of RNA oligomer formation in aqueous solution a model for the prebiotic formation of RNA. J. Am. Chem. Soc., 115, 12270-5. 

We now have seven candidates, and the phase rule allows seven phases to be stable together. We shall state as a working hypothesis that these seven phases—(1) aqueous solution, (2) quartz, (3) kaolinite, (4) hydromica (illite) (5) chlorite, (6) montmorillonite, and (7) phillip-site—are the stable assemblage in the intermediate model, and we shall test this hypothesis against various evidence. Some of these phases may prove unstable and be replaced by some other phase—e.g., phillipsite by another zeolite or a feldspar. Chlorite might also be replaced by some of the magnesium silicates described by Arrhenius (3). 

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