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Sepiolite is a hydrous magnesium silicate of the same family of clays as attapulgite. It differs from bentonites (montmorillonites) in that it has no substitutions in its lattice structure. Although on a molecular scale, sepiolite retains the three-layer structure of the other two clays, the crystals are much more highly ordered and contain very few of the crystal imperfections which give rise to cation exchange capacity. In order to keep the nearly perfect balance of positive and negative ionic changes, the crystals are limited in their growth to a width of only 6 silica tetrahedra; however their length is unlimited. The nearly perfect crystal structure contributes to the high thermal stability of sepiolite, and the “ribbon-shaped” crystals help impart viscosity to aqueous suspensions.
Sepiolite, like attapulgite, but unlike bentonite and saponite, is unaffected by elecrolytes and can gel salt solutions. Sepiolite is very similar to attapulgite in most applications, but since the sepiolite “ribbons” are more flexible than attapulgite “needles’, sepiolite becomes more efficient in some applications, such as asbestos replacement and reinforcing systems. Sepiolite is an excellent binder.
IMV Nevada is fortunate to possess the only commercial deposit of sepiolite in North America.
IMV’s bentonite is a calcium based montmorillonite, having an unusually well developed dioctahedral crystalline structure. It is white to off-white in color. In addition to the well developed crystalline structure, this bentonite has an extremely high cation exchange capacity.
Saponite is similar to sodium bentonite (montmorillonite) except that magnesium (MgO) has replaced all or most of the aluminum as well as the exchangeable sodium. It has a trioctahedral structure and a flat tubular mica-like crystal with a fuzzy edge. It is a swelling clay having a low cation exchange capacity and imparts thixotropy to aqueous solutions. Saponite has the same uses as bentonite, but is more stable because of its much lower cation exchange capacity.