Research progress on the synthesis of zeolite from industrial ash rich in silicon and aluminium

A series of porous silicon aluminate materials is defined as zeolite, which is widely used in sewage purification, catalytic chemical synthesis and other fields due to its higher cation exchangeability. Coal ash, gasification ash, casting ash, and other industrial ashes may be used as the main raw materials for the synthesis of zeolite because they contained a large number of Si and Al elements, to achieve the purpose of resource utilization of these solid wastes. The formation and sources of coal ash, gasification ash and casting ash were analyzed. By comparing their chemical composition contents, it was found that the chemical composition contents of coal ash followed the order of SiO₂>Al₂O₃>Fe₂O₃>CaO. The ignition loss of gasification ash was 36.1%, which was relatively higher, and the ratio of Si to Al was significantly higher in casting ash than those in gasification ash and coal ash. At present, among the three kinds of ashes, more research and utilization work had been done for coal ash, while less had been done for casting ash and gasification ash. The total content of Al₂O₃ and SiO₂ in casting ash was relatively high, and its loss on ignition and metal oxide content was low. Casting ash was a high-quality raw material, which could be used to prepare high-quality zeolite. In addition to considering the recovery and utilization of Si and Al of gasification ash, its residual carbon should be fully utilized because the residual carbon content of gasification ash was relatively high.