Determining suitability of a fly ash for silica extraction and zeolite synthesis

Abstract

Abstract Zeolitic material is obtained from fly ash both by direct conversion of the ash or from SiO 2 extracts obtained from fly ash. This study focuses on determining the suitability of a fly ash for SiO 2 extraction and for zeolite synthesis by direct conversion. The SiO 2 extraction experiments from different fly ashes show that the main parameters governing the SiO 2 extraction are: (a) a high bulk SiO 2 content (>52%, for obtaining an extraction yield of 100 g SiO 2 kg −1 ) in the starting fly ash, (b) a high proportion (>55%) of the bulk SiO 2 present in the degradable glass matrix and the highly soluble opaline fraction, and (c) a high bulk SiO 2 /Al 2 O 3 ratio (>2.0) of the fly ash. The results from experiments of zeolite synthesis by direct conversion demonstrate that the most important criteria for the selection of a fly ash for this process are: (a) a high content of Al 2 O 3 and SiO 2 (>65%) (b) a high glass content (>63%) and (c) relatively low SiO 2 /Al 2 O 3 ratio (<2.0). Multivariate analysis confirms the importance of the above‐mentioned variables and shows some additional variables that have influence on ash behaviour under alkaline conditions. It quantifies the use of those variables for determining the suitability of ashes for SiO 2 extraction and zeolite synthesis and is able to distinguish between the two. Copyright © 2004 Society of Chemical Industry