Cation-exchange capacity aluminosilicate minerals

The use of surfactant-modified zeolite (SMZ) as a permeable barrier sorbent may offer several unique advantages when dealing with mixed contaminant plumes. Zeolites are hydrated aluminosilicate minerals characterized by cage-like structures, high internal and external surface areas, and high cation exchange capacities. Both natural and synthetic zeolites find use in industry as sorbents, soil amendments, ion exchangers,... 

Cans, at the turn of the 19lh century, synthesised aluminosilicate materials capable of water softening. He called them Permutits and for many years they were employed as domestic and industrial water softeners, as well as in the treatment of nuclear waste. This, together with the first identification of base exchange in soils (Way [2] and Thompson [3 J), led to the misunderstandings perpetuated in elementary texts that zeolites are responsible for the ion-exchange in soils, and that they are widely used as water softeners. In truth the clay minerals contribute mainly to the ability of soils to take up cations, such as ammonium, and Permutits were amorphous materials with low cation exchange capacities and limited chemical stability. 

A zeolite, of course, is a crystalline aluminosilicate mineral with a very open pore structure and a very large water adsorption capacity. It possesses two well-defined chemical properties. First, it can be reversibly hydrated and dehydrated. Second, it has a high reversible ion exchange capacity. This capacity corresponds to one equivalent of cation per A1 atom in the anionic framework. The anionic nature of the framework derives from the substitution of trivalent A1 atoms for Si atoms in the tetracoordinated structure. 

---