What Are Zeolites?

2215 WordsFeb 23, 20189 Pages
What are zeolites? According to (ref) the mineralogist community define a zeolite as a ‘crystalline aluminosilicate, with 4-connected tetrahedral framework structure enclosing cavities occupied by large ions and water molecules, both of which have considerable freedom in movement, permitting ion exchange and dehydration’. This definition allows us to evaluate three components of a zeolite; a 4-connected framework, counter balancing ions (also referred to as an extra framework ion) and an adsorbed phase (in this case it is the water molecules within the structure.). Due to the diverse nature of the zeolite family, they exist in many forms differing in structure and chemistry, therefore the definition proposed above is restricted to certain types, aluminosilicates. Therefore, among minerals we will familiarise ourselves with materials that carry zeolite properties but are not equivalent to the definition proposed by mineralogists. One example would be the mineral wenkite; it has an interrupted framework with only 3 oxygen’s coordinated to the silicon atom, [O3-Si-OH]. Regardless of this difference and any other differences apparent in a zeolite mineral they still belong to the zeolite family. Therefore, a more deviated definition which considers all zeolites is a zeolite is an open framework composed of voids and pores where the movement of ions and molecules are not limited. Zeolite minerals share the general formula Mm+ . [Si1-xAlxO2] . nH2O where M is a metal cation, Mm+
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