Isomorphous substitution hectorite

The other key difference is the level and type of isomorphous substitution in each of these minerals. Among the trioctahedral clays, talc has no isomorphous substitution, hectorite has moderate substitution of Li for Mg and vermiculite and mica have high levels of substitution. 

In montmorillonite some of the Al3 + in the octahedral sublattice are replaced by Mg2+ ions, and in hectorite some of the Mg2 + in the octahedral sublattice are replaced by Li+ ions. With beidellite and saponite, however, the isomorphous substitution takes place in the tetrahedral sublattice with Al3 + replacing some of the Si4+ ions. The residual negative charges in the layers on montmorillonite, hectorite, beidellite, and saponite are counterbalanced in the natural state by coexisting interlamellar, hydrated cations, usually Na+,... 

In order to systematically change the properties of layered silicate materials, we have investigated the possibility of isomorphous substitution of silicon by aluminum or boron. It is demonstrated that addition of horon and/or aluminum compounds to the reaction mixture leads directly to boron and aluminum containing layered materials in a hydrothermal crystallization process without further treatment. The layered materials obtained were identified as hectorite types, magadiite and kenyaite-like types. The isomorphous substitutions were proven by "B, Al, and Si solid state NMR spectroscopy. 

Hectorite is an aluminum-free mineral of the smectite type. Isomorphous substitution could occur at tetrahedral silicon sites as well as at the octahedral sites originally occupied by lithium and magnesium. Monitoring the x-ray powder diffraction patterns as a frmction of crystallization time, it was found that the hydrothermal crystallization was complete after 12h at 200°C, independent of the alumina content of the reaction mixture. However, NMR spectroscopy proves that some structural change still occurs after this time period. 

Figures 1 and 2 are snapshots of equilibrium interlayer configurations, based on MC simulations (27), in Li-beidellite (Lio75[Si7 25AlQ75]Al402o(OH)4), which has isomorphic substitutions only in its tetrahedral sheets, and in Li-hectorite...

Laponite RD is a fnlly synthetic clay similar in structure and composition to natural hectorite of the smectite group (Scheme 1). Each layer is composed of three sheets two outer tetrahedral sihca sheets and a central octahedral magnesia sheet. Isomorphous substitution of magnesium with Uthium in the central sheet creates a net negative charge compensated by intralayer sodium ions located between adjacent layers in a stack. The cation exchange capacity of Laponite is 0.75 meq The dimen-... 

This particle is naturally occurring and found around the world. It is easily mined and purified. The reactor for the particle was a volcano. The ash from many volcanoes was spread around the earth during an intense period of activity many millions of years ago. This ash was transformed into clay (montmorillonoids or smectites) by natural processes, into uncharged species (talc and pyrophyllite) and charged species through isomorphic substitution of the crystal structure (hectorite, montmorillon-ite, saponite, suconite, volchonskoite, vermiculite, and nontronite). 

Hectorite is the isomorphic substitution of Li for Mg (from talc). Some isomorphic substitution is observed in the tetrahedral silica dioxide layer with A1 substituting for Si. These particles are found in nature in stacked arrays similar to a pad of paper. They can be easily mined and purified by dispersing the montmorillonite into water and removing the larger, heavier particles (sand, gravel, etc.) by centrifugation. 

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