Smectite, Wyoming bentonite

Figure 3.2. Dependence of f-values of adsorbed cations on the mole fraction of exchange sites occupied by Rb and Na in the NaV b and Li+/Na+ exchange reaction on smectite. Adapted from R. G. Cast. 1969. Standard free energies of exchange for alkali metal cations on Wyoming bentonite. Soil Sci. Soc. Am. Proc. 33 37-41 1972. Alkali metal cation exchange on Chambers montmorillonite. Soil Sci. Soc. Am. Proc. 36 14-19.)...

Fig. 1. Hydroxyl absorption bands for several smectites pillared with aluminum chlorhydroxide (ACH) soluctions A) Wyoming ACH-bentonite B) Texas ACH-bentonite C) Fe-bentonite D) ACH- Fe bentonite) E) (ACH, Fe)-bentonite and F) ACH-nontronite. Samples a) have been dried at 200 C and then loaded with pyridine and degassed at b) 200 C, c) 300 C, d) 400 C and e) 500 C in vacuo for 2 hours at each temperature.

Bentonite is a native colloidal hydrated aluminum silicate or clay found in the midwest United States, Wyoming, and Canada. Consisting mainly of montmorillonite, a smectite clay, it is a very fine, odorless, pale buff or cream colored to grayish powder. It consists of particles in the range of 50 to 150 microns, but also has numerous particles in the 1 to 2 micron range. 

Smectite - The smectites are water swellable cl s having a sheet or platelet structure. Smectite is the mineralogical term for this class of clays, which includes montmorillonite, hectorite, and saponite. Montmorillonite clays derive their name from the Montmorillon section of France where this material was first observed and later classified. Most smectites are more commonly known under the geological term bentonite. By convention, a bentonite is understood to be an ore or product with a substantial smectite content. The name bentonite derives from Fort Benton, Wyoming, the site of an important deposit. Lattice substitutions within the smectite clays creates a charge imbalance which is compensated by exchangeable alkali and alkaline earth cations. This contributes to the ability of these clay to swell and impart considerable plasticity in ceramic formulations. When the exchangeable cations are predominately sodium, the individual platelets can separate to produce a colloidal structure in water. 

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