The commercial production of detergent zeolite A is mainly conducted using the aluminosilicate hydrogel route using sodium silicate and sodium aluminate [4]. Cheaper raw materials such as clay minerals, coal ashes, natural zeolites, municipal solid wastes and industrial sludge have been widely tested [5,6]. Among these naturally available raw materials, kaolin which has Si/Al ratio of nearly 1 similar to zeolite A has been used as alternative cheap rawmaterial for the synthesis of zeolite A [7]. The synthesis of zeolite A from kaolin involves two basic steps: metakaolinization, which is the calcination of the raw kaolin at high temperature to change chemically stable kaolin into a very reactive but amorphous material, metakaolin, and hydrothermal treatment of the calcined kaolin with sodium hydroxide.
Kaolin (Al2O3$2SiO2$2H2O) in its natural state is less reactive.Metakaolin (Al2O3$2SiO2), a calcined product of kaolin with Si/Al ratio of 1 is a convenient starting material for the synthesis of zeolite A. This process is usually performed between 550 and 900 C [8]. The synthesis of zeolite A from kaolin source started in
the 1970s by the hydrothermal reaction of dehydroxylated kaolin with sodium hydroxide solution [9]. During the past four decades, there have been relevant studies and patents reported in this area trying to minimize the synthesis cost with good quality of pure zeolite A.V. Sanhueza et al. synthesized zeolite A type from Chilean kaolinites in which the best conditions for synthesis were SiO2/Al2O3 ¼ 2.5, Na2O/SiO2 ¼ 1.0, H2O/Na2O ¼ 50 and 15 h reaction time at 100 C