“…Because fly ash is composed of 24-27% lime and a portion of silicates and aluminosilicates [6], it is used as a raw material for civil materials, such as conventional ceramics, ceramic aggregate, clay brick, cement clinker and other raw material substitutions [7][8][9][10]. In these processes, the thermal treatment with a high temperature is a common method for fly ash consumption, where the contamination (dioxin and heavy metals) is decomposed (for dioxin) or encapsulated in a silicate-based glass-like matrix (for heavy metals) [11][12][13][14]. In particular, the toxicity characteristic leaching procedure (TCLP) results for heavy metals in the matrix are below than the national regulation limitation, indicating the high stability of heavy metals [15,16].…”