Producing a synthetic zeolite from improved fly ash residue

Fly ash, if not utilised, is considered a waste product. Zeolitisation of coal fly ash offers the opportunity to create an added value product from a waste stream. Using a two-step zeolitisation process, Si is leached from improved fly ash residue — a previously untested feedstock for this process. Optimisation of the conditions of crystallisation of synthetic zeolite are discussed in this paper. The type of synthetic zeolites produced was found to be highly dependent on the conditions of the crystallisation process. Zeolites formed include zeolite Na-P1, sodalite, zeolite Na-A, zeolite K-A, and others. Crystallisation parameters explored in this paper include sodium aluminate addition, duration of crystallisation period, temperature, and the type of fly ash (improved fly ash residue vs. untreated fly ash). Yields of up to 250 g/kg of ash of high purity zeolite Na-P1 were produced from improved fly ash residue. Although this is an improvement on yields in literature, tentative profitability calculations on a full scale plant require a yield of 286 g/kg ash in order to achieve a return on investment within 4 years.