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 a lkaline solutions is a well known process which, however, usually results i n a zeolitic product which still contains significant amounts of residual f ly 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 o f fly ash prior to the residual being converted into zeolite by the traditi onal method. The cation exchange capacities ranged from 3.6 to 4.3 meq/g fo r the pure zeolites and from 2.0 to 2.5 meq/g for the zeolite containing re sidual fly ash. Tests showed that the pure zeolites an suitable for the rem oval of ammonium and heavy metal ions from waste water. (C) 1999 Elsevier S cience Ltd. All rights reserved.