P. Sidheswaran et An. Bhat, SYNTHESIS OF SODALITEHYDRATE FROM CLAYS, Indian journal of chemistry. Sect. A: Inorganic, physical, theoretical & analytical, 36(8), 1997, pp. 672-676
Synthesis of zeolites fi om clays requires more than stoichiometric qu
antity of caustic soda. It has been believed that apart from solubilis
ing alumina and silica, excess sodium ions in caustic soda are involve
d as templates in the synthesis of zeolite. Clays (kaolin, bentonite a
nd pyrophillite) have been examined for the preparation of sodalitehyd
rate using caustic soda. Extents of sodalitehydrate formation is diffe
rent for different clays (similar to 38% for bentonite, 50% for pyroph
illite and about 95% each with kaolinite and metakaolinite). It is fou
nd that sodium ions of electrolytes (NaCl and Na2SO4) in fact template
the zeolite synthesis, and can be used to replace a major part of the
alkali. Thus, the system with 0.5 N NaOH and electrolyte produces abo
ut 85% sodalitehydrate. In the absence of electrolyte, it is necessary
to have 8 N NaOH. This substantiates the templation of zeolites by so
dium ions.