Synthesis of 4A-type zeolite from calcined Nigerian kaolinitic clays

Abstract

The 4A type zeolite was produced through a synthesis of sodium aluminate based on a special hydrothermal procedure from Nigerian kaolinitic clays. The kaolinitic clays which coexist with quartz, were thermally activated within the temperature range of 750 °C to 1,000 °C and treated hydrothermally with 2 to 9 molar solutions of NaOH without added water glass using a laboratory reactor. The reacted products were identified as 4A type zeolite, faujasite (Y type zeolite) and gelatinous, amorphous material (hydroxysodalite). The syntheses of these reacted products depend on the calcination temperature of the kaolins, concentration of NaOH and the reaction time. The quality of 4A zeolite produced from both kaolins at 750 °C and 850 °C showed close characteristics in terms of brightness, crystal size and degree of crystallinity. The results are compared with those obtained in the synthesis of zeolites from soluble salts. At calcination temperatures of 1000 °C and higher alkalinity hydroxysodalite replace all previous zeolites. It is concluded that the kaolinitic clays were used as the supplier of the silica and alumina units necessary to synthesize the zeolites.