On the state of the art of crystalline structure reconstruction of coal fly ash: A focus on zeolites

Abstract Coal fly ash (CFA) is fine particles generated from coal combustion, and large amount of CFA causes environmental pollution. Traditionally, CFA is added into construction materials, which has realized effective reduction. As the exploration of CFA properties goes deeper, finer utilization has been studied to maximize the recycling of CFA. Summarized from plenty of investigations, structure reconstruction has become the most crucial part for re-production as well as pre-treatments. Various zeolites and other complex materials have been synthesized by structure reconstruction. In this work, the state of the art of structure reconstruction were technically collated in the order of pre-treatments, mechanisms, specific techniques, and novel optimizing strategies. It has been found the crystalline types are closely related to the reaction conditions, that certain types of products could be obtained via accurate condition controls, especially the ratio of Si to Al. The current as-synthesized products were listed as well as their crystalline structure characteristics. Recently, combined materials and techniques have been innovatively investigated. However, the challenge remains as low purity, not only impurities in CFA but also different types of zeolites formed in one process.