Zeolites

Zeolites are a well-established technology used in a range of processes and industries. Zeolites are not new materials—they have been investigated for over two and a half centuries, with stilbite and natrolite both being identified in the 1750s. Industrial applications include catalysis in the petroleum industry (Venuto and Dekker 1979, Chen et al. 1994), various uses in agriculture (St. Cloud 2007, BRZ Zeolite 2007, Zeolite Australia 2007), horticulture (ZeoPro 2007), gas separations (Yang 1994, Kerry 2007, Kanellopoulos 2000), domestic water treatment (McKetta 1999, Kawamura 2000, Faust 1998); and nuclear waste processing (Auerback et al. 2003, Choppin and Khankhasayev 1999). The value of zeolite catalysis to petroleum cracking is well in excess of $200 billion (MassNanoTech 2007). About 50 naturally occurring zeolites have been identified; over 150 synthetic zeolites have been prepared and characterized; and further thousands of combinations of framework and composition are available (MassNanoTech 2007, Baerlocher and McCusker 1996). Zeolites have long been used in the nuclear industry (Auerback et al. 2003, Choppin and Khankhasayev 1999) owing to their properties as ion exchangers. The planned siting of the United States’ first deep geologic radioactive waste repository at Yucca Mountain in Nevada, where design philosophy called for both engineered and natural barriers (Ahn et al. 1981) to inhibit the transport of any potentially leaking radionuclides, was influenced considerably by the local abundance of the natural zeolites mordenite and clinoptilolite, both of which have large cationic exchange capacities.