A two-step process for the synthesis of zeolites from coal fly ash

The conversion of fly ash into zeolites by incubation of the fly ash with alkaline solutions is a well known process which, however, usually results in a zeolitic product which still contains significant amounts of residual fly ash. Presented here is a method by which part of the silicon in fly ash can be used for the synthesis of a maximum of 85 g of pure zeolite per kg of fly ash prior to the residual being converted into zeolite by the traditional method. The cation exchange capacities ranged from 3.6 to 4.3 meq/g for the pure zeolites and from 2.0 to 2.5 meq/g for the zeolite containing residual fly ash. Tests showed that the pure zeolites an suitable for the removal of ammonium and heavy metal ions from waste water. (C) 1999 Elsevier Science Ltd. All rights reserved.