Abstract:Circulating fluidized bed (CFB) fly ash is regarded as the main solid waste produced in the process of coal combustion. CFB fly ash is not applied in building materials due to its high content of Ca, which causes serious pollution. The occurrence of Ca and distribution of calcium-containing phases in CFB fly ash was revealed. The results show that amorphous aluminosilicate, quartz, Ca(OH)2, CaSO4, and a small amount of CaPO3(OH) are contained in CFB fly ash. The occurrence forms of calcium are mainly divided into two kinds. Most of calcium is combined with aluminosilicate minerals, and is incorporated into aluminosilicate minerals to form solid melt, while a small part exists in the form of calcium sulfate. Based on the occurrence of Ca, a novel method of selective removal of Ca by control of pH value is proposed, the concentration of Ca2+ in the solution can be enriched to more than 20 g/L, and the removal rate of Ca is 80% under the optimal conditions, and the content of CaO is 5% below, which can meet the requirements of building materials utilization standards.