Montmorillonite, sodium

To obtain a high viscosity at a much lower clay concentration, certain water-soluble vinyl polymers called clay extenders can be used. In addition to increasing the yield of sodium montmorillonite, clay extenders serve as flocculants for other clay solids. The flocculated solids are much easier to separate using solids control equipment. 

The clay mineral bentonite (sodium montmorillonite) has an excellent ion exchange and adsorption capacity. Films can be applied to electrode surfaces from colloidal clay solutions by simple dip or spin coating that become electroactive after incorporation of electroactive cations or metal particles 136-143)... 

Osmotic swelling is a second type of swelling. Where the concentration of cations between unit layers in a clay mineral is higher than the cation concentration in the surrounding water, water is osmotically drawn between the unit layers and the c-spacing is increased. Osmotic swelling results in larger overall volume increases than surface hydration. However, only certain clays, like sodium montmorillonite, swell in this manner. 

Nonionic cellulose ethers, hydroxyethyl(HE) and hydroxypropy1 (HP) cellulose, of variable molar substitution (M.S.) levels, were adsorbed on peptized sodium montmorillonite surfaces from fresh and saline (NaCl) aqueous solutions. The amounts adsorbed for 2 M.S. HEC and HPC and 4 M.S. HEC were insensitive to electrolyte concentration the 4 M.S. 

HPC exhibited a notable increase in adsorption with increasing NaCl concentration. Entrapment in the interlayer of recovered sodium montmorillonite did not vary with salinity the extent of entrapment was greater with the 4 M.S. HE and HP celluloses than either of the 2.0 M.S. polymers. Mixed ethers of HEC (2 M.S.) containing an anionic (carboxymethyl) or cationic (3-0-2-hydroxypropyltrimethylaramonium chloride) group at 0.4 M.S. levels did not adsorb from fresh water. Adsorption of these polar mixed ethers increased with increasing electrolyte until electrostatic and solvation effects were negated in 0.54N NaCl solutions and the adsorbed amounts typical of a 2 M.S. HEC were observed. Interlayer entrapments comparable to the equivalent M.S. HEC were observed at lower (0.18N) electrolyte concentrations. 

ADSORPTION AND INTERLAYER EXPANSION OF CELLULOSE ETHERS FROM FRESH WATER ON PEPTIZED SODIUM MONTMORILLONITE... 

Figure 7 Adsorption (g/g) dependence of nonionic and ionic cellulose ethers (2500 ppm) on salinity (N, NaCI) of aqueous solution.Substrate peptized sodium montmorillonite. W-SP symbols given in Figure 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. 

Also, sodium montmorillonite-modified carbon paste electrode has been used for the determination of trace concentrations of mercury [80]. Hg + was preconcentrated at the electrode, reduced, and then stripped from the electrode surface in the positive potential scan. At a glassy carbon electrode modified with dithizone, mercury has been determined, applying anodic stripping voltammetry [81]. 

Paechthorowitz, M. and Eirich, F. R. (1988). The polymerisation of amino acid adenilates on sodium montmorillonite with preadsorbed polypeptides. Orig. Life Evol Biosph., 18, 359-87. 

Sodium montmorillonite clay particles ot-Fe203 prepared in clay particles... 

The morphology of rubber-based nanocomposites also seems to change in the presence of compounding ingredients [89, 90]. HNBR, when melt-compounded with organo-modified sodium montmorillonite clays (o-MMTs) prior to sulfur curing, resulted in the formation of nanocomposites with exfoliated or intercalated structures. In stark contrast, under similar conditions HNBR compounded with unmodified sodium montmorillonite clays (NA) formed microcomposites [90]. This was traced to its reactivity with the sulfur in the presence of amine-type organomodifiers. 

The intercalated cationic radical initiator was synthesized from 2,2 -azobis[2-methyl-N-(2-hydroxyethyl) propionamide] by esterification with bromoacetyl bromide, and subsequent quaternization with tributylamine. Sodium montmorillonite was suspended in deionized water. The cationic radical initiator was bound onto the montmorillonite by ion exchange. 

Cowan, C. T., and D. White, The mechanism of exchange reactions occurring between sodium montmorillonite and various n-primary aliphatic amine salts , Trans. Faraday Soc., 54, 691-697 (1958). 

Sodium bentonite with a cation exchange capacity (CEC) of 75 meq/100 g of clay, supplied by Commercial Minerals Ltd., Australia, was used as starting clay material, to prepare samples for SCD and surfactant treatments. Besides, sodium montmorillonite (Kunipia G), from Kunimine Industrial Company, Japan, was used as the starting clay for samples of pore opening modification. CEC of this clay is 100 meq/100 g of clay. 

Some experiments have been carried out with a sodium montmorillonite dispersion on an Sn02 electrode.77 The layer of clay adhered well to the surface and [Ru(bipy)3]2+ was successfully exchanged on to the clay. The film was electroactive but cracked readily. The addition of powdered platinum gave a more coherent layer. Other species exchanged on to the clay included [Fe(bipy)3]2+ and a trimethylammonium derivatized ferrocene. 

Original kaolinite Sodium kaolinite Ammonium kaolinite Hydrogen kaolinite Original montmorillonite Sodium montmorillonite Ammonium montmorillonite Hydrogen montmorillonite... 

Hu et al. [84] Hypoxanthine Fish Xanthine oxidase/within a polyaniline film on the electrode surface by electropolymerisation Sodium montmorillonite-methyl viologen carbon paste modified electrode/-0.72V vs. Ag/ AgCl Methyl viologen... 

Ottewill and co-workers106,200 have used a compression method to measure the double-layer repulsion between the plate-like particles of sodium montmorillonite. This is a particularly suitable system for such studies, since the particles are sufficiently thin (c. 1 nm) for van der Waals forces to be unimportant and surface roughness is not a problem. The dispersion was confined between a semipermeable filter and an impermeable elastic membrane and an external pressure was applied via a hydraulic fluid so that the volume concentration of particles and, hence, the distance of separation between the particles could be measured as a function of applied pressure. 

In these experiments a commercially available bentonite, marketed under the name Colclay A90 (Ankerpoort, Geertruidenberg, The Netherlands) was used. It is a sodium-montmorillonite with a third of the exchange complex occupied by calcium. 5.0 g of the air-dried powdered bentonite was weighed into a stainless steel mould with an ID of 50 mm between two porous stones of the same diameter. Then the clay was subjected to a compaction pressure of 20.3 MPa for 30 minutes. After compaction, the mould was placed in a bowl of NaCl-solution for five days in which the clay became saturated and swollen. Thus samples were obtained with thickness of 3.8 and 2.8 mm respectively and a diameter of 50 mm. 

Figure 5.19 The specific volume offilter cake, sediment volume, and Bingham yield stress of sodium montmorillonite sols as a function of the NaCI concentration. From van Olphen [1], Copyright 1977, Wiley-lnterscience.

---