Montmorillonite ordering

Figure 8.18. Adsorption isotherm of six. v-triazines on Na-montmorillonite. Order of solubility simetone > atratone > promatone > atrazine > trietazine > propazine (from Bailey et al., 1968, with permission).

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. 

The great importance of minerals in prebiotic chemical reactions is undisputed. Interactions between mineral surfaces and organic molecules, and their influence on self-organisation processes, have been the subject of much study. New results from Szostak and co-workers show that the formation of vesicles is not limited to one type of mineral, but can involve various types of surfaces. Different minerals were studied in order to find out how particle size, particle shape, composition and charge can influence vesicle formation. Thus, for example, montmorillonite (Na and K10), kaolinite, talc, aluminium silicates, quartz, perlite, pyrite, hydrotalcite and Teflon particles were studied. Vesicle formation was catalysed best by aluminium solicate, followed by hydrotalcite, kaolinite and talcum (Hanczyc et al., 2007). 

Jackbean urease was immobilized on kaolinite and montmorillonite [98]. The amounts of urease required for maximum immobilization were 70 and 90 mg g 1 of kaolinite and montmorillonite, respectively. The Km values of immobilized urease (25.1-60.8 mM) were of the same order of magnitude as that of free urease (29.4 mM) but one order of magnitude higher than those of soil urease (1.77-2.90 mM). Immobilization of urease on clay surfaces leads to increases in the kinetic constants. 

Ti(H), for intercalated Ph is more than four orders of magnitude shorter than that for the pure compound. Equally striking is the close similarity of the Ti(H) value between TDTMA and Ph in the TDTMA-montmorillonite-Ph interlayer complex. All these observations strongly indicate that the TDTMA chains become relatively disordered and closely mixed with Ph in the interlayer space of montmorillonite. 

The authors [1] studied kinetics of poly (amic acid) (PAA) solid-state imidization both in the presence of nanofiller (layered silicate Na+-montmorillonite) and without it. It was found, that temperature imidization 1] raising in range 423-523 K and nanofiller contents Wc increase in range 0-7 phr result to essential imidization kinetics changes expressed by two aspects by essential increase of reaction rate (reaction rate constant of first order k increases about on two order) and by raising of conversion (imidization) limiting degree Q im from about 0,25 for imidization reaction without filler at 7 i=423 K up to 1,0 at Na -montmorillonite content 7... 

The true gas phase basicity order is observed in the montmorillonite (43), whereas in solution the well known amine anomaly exists, i.e. the expected inductive effects of the organic carbon chain are screened off by the solvent. For example, identical AG values of protonation are found in solution for methyl- and butylammonium. 

Exchange in zeolites of alkali, alkaline earth, transition metal ions and small organic ammonium ions, has been reviewed (111), and in general, the exchange is characterized by small AG values comparable to those found in clay minerals. Althoufft identical selectivity orders for alkali and alkaline earth metal ions are obtained, as in montmorillonite, the opposite variation of AG with charge density is found. 

However, when protonated TEMPAMINE adsorbs by cation exchange on fully hydrated layer silicate clays (10, 11), the spectrum becomes less symmetrical as shown in Figure 5. The beidellite and montmorillonite spectra have line shapes typical for nitroxide molecules with rotational frequencies on the order of 10 Hz (17). 

Chlorpyrifos is stable to hydrolysis in the pH range of 5-6 (Mortland and Raman, 1967). However, in the presence of a Cu(lf) salt (i.e., cupric chloride) or when present as the exchangeable Cu(II) cation in montmorillonite clays, chlorpyrifos is completely hydrolyzed via first-order kinetics in <24 h at 20 °C. It was suggested that chlorpyrifos decomposition in the presence of Cu(II) was a result of coordination of molecules to the copper atom with subsequent cleavage of the side chain containing the phosphorus atom forming 3,5,6-trichloro-2-pyridinol and 0,0-ethyl-0-phosphorothioate (Mortland and Raman, 1967). 

Based on these rate laws, various equations have been developed to describe kinetics of soil chemical processes. As a function of the adsorbent and adsorbate properties, the equations describe mainly first-order, second-order, or zero-order reactions. For example. Sparks and Jardine (1984) studied the kinetics of potassium adsorption on kaolinite, montmorillonite (a smectite mineral), and vermiculite (Fig. 5.3), finding that a single-order reaction describes the data for kaolinite and smectite, while two first-order reactions describe adsorption on vermiculite. 

The Li ions were introduced in two different ways either before or after Zr intercalation. The montmorillonite (Weston L-Eccagun) was first exchanged with NaCl (IN) and washed. Two montmorillonites with reduced charge were prepared following the Brindley and Ertem method (13). Part of the Na+ montmorillonite was first saturated with LiCl (IN) and washed. The Li+ clay thus obtained and Na+ clay suspension were stirred for 24 hours at 25°C and dried on glass plate. The films were then heated at 220°C for 24 h in order to allow Li diffusion in the clay structure. Two different Li concentrations (F=0.4 and F=0.6) were used. The Na Li+ modified montmorillonite were dispersed in water acetone solution (1/1). The ZrOCla, 8H2O solution was added to the Na+Li+ montmorillonite (0.02g.l l Zr/Clay=5.CEC). The suspension was stirred with NaOH solution (0.1 N) up to a OH/Zr ratio of 0.5. The final pH of the suspension was 1.85. After two hours of reaction at 40°C the Zr pillared clay was washed up to constant conductivity of the solution, freeze-dried and calcined at different temperatures up to 700°C (Eni-02 and EIII-03). 

Figure 18. Schematic representation of several possible types of solid solution. Shaded and blank layers represent expanding and mica-like units (2 1 structures). Solid and unfilled circles represent two species of interlayer ions, a totally random in all aspects b = interlayer ion ordering, single phase montmorillonite c = ordered interlayer ions which result in a two-phase mica structure, two phases present d = randomly interstratified mineral, one phase e = regular interstratification of the 2 1 layers giving an ordered mixed layered mineral, one phase present f = ordered mixed layered mineral in both the interlayer ion sites and the 2 1 interlayering. This would probably be called a single phase mineral.

---