Effective utilization of coal fly ash containing unburned carbon

We investigated the conversion process of coal fly ash with unburned carbon at greater than ca. 6 mass%, which has fallen behind in terms of resource recovery. As a result, composite materials consisting of zeolite A and/or zeolite X with good crystallinity and activated carbon were successfully prepared by NaOH fusion treatment at 750°C in N2 flow followed by hydrothermal treatment. The type of zeolite phase formed was dependent on the hydrothermal treatment conditions including NaOH concentration. The resulting composite materials exhibited removal characteristics for heavy metal ions such as Ni²⁺, Cd²⁺ and Pb²⁺. In this paper, we describe the conversion of the main SiO₂-Al₂O₃ components and unburned carbon in coal fly ash into zeolite-activated carbon composite materials by a chemical process and the removal characteristics of the resulting materials.