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• The ceramsite was successfully produced using solid waste including MSWI fly ash. • The raw material ratio and sintering condition of ceramsite was optimized. • The heavy metals (HMs) were well immobilized in ceramsite. • HMs immobilization was mainly due to glass phase and formation of new crystal phases. With an increase in municipal solid waste incineration (MSWI) fly ash and its dangerous characteristics, the manner of its disposal has caused widespread concerns. In this study, ceramsite was prepared by using MSWI fly ash, civil sludge, and contaminated soil as the main raw materials; then, a certain proportion of clay was added as an additive. The optimum MSWI fly ash content and sintering conditions were investigated, and the immobilization mechanisms of heavy metals were explored. Based on the obtained results, the optimum preparation conditions were a preheating temperature of 400 °C, a preheating time of 10 min, a sintering temperature of 1150 °C, and a sintering time of 20 min. Moreover, the optimal raw material ratio of MSWI fly ash, civil sludge, contaminated soil, and flint clay was 30%:40%:15%:15%. Under these optimum preparation conditions, the obtained ceramsite showed the following excellent performance parameters: a 1-h water absorption of 0.97%, bulk density of 998.7 kg/m3, and cylindrical compressive strength of 37.84 MPa. Furthermore, the leaching of heavy metals was far less than the standard GB5085.3-2007. The immobilization of heavy metals in the ceramsite was mainly caused by the glass phase encapsulation and the formation of new crystal phase with the heavy metals. In addition, the generation of aluminosilicates played a positive role in the immobilization of heavy metals. Thus, the reuse of MSWI fly ash by preparing fly ash-based ceramsite is one of the effective methods for reducing solid wastes. [ABSTRACT FROM AUTHOR]

• ● The ceramsite was successfully produced using MSWI fly ash and granite sawing mud. • ● The raw material ratio and sintering condition of ceramsite was optimized. • ● Chlorine in MG ceramsite mainly enters into the tail gas and secondary fly ash. • ● Chlorine salts are the main chlorine speciation after sintering. Municipal solid waste incineration (MSWI) fly ash is a hazardous waste containing high chlorine and harmful substances generated during the waste incineration disposal, and its resource utilization has a positive effect on reducing environmental pollution. In this study, the feasibility of preparing lightweight MSWI fly ash/granite sawing mud ceramsite (MG ceramsite) was investigated by evaluating the influence of Al 2 O 3 addition, MSWI fly ash content and sintering temperature on the ceramsite properties. The microstructure of MG ceramsite was investigated by using SEM, the chlorine morphological transformation and migration behaviors were simultaneously explored by using the tube furnace experiment, XRD and XRF analyses. The experimental results show that the maximum MSWI fly ash content is about 30 wt%∼35 wt%, with the Al 2 O 3 addition of at least 10 %. By controlling the MSWI fly ash content of 30 wt%, MG ceramsite can be obtained with bulk density of 986 kg/m3, cylindrical compressive strength of 19.67 MPa, 1 h water absorption of 0.31 %, and chlorine content of 0 after sintering at 1150 °C for 20 min. Chlorine in MG ceramsite enters into the tail gas or secondary fly ash in the form of chlorine salts and chlorine-containing gas when the sintering temperature is above 800 °C. The MG ceramsite prepared from MSWI fly ash meets the lightweight aggregate standard and are environmentally friendly. However, the disposal of tail gas and secondary fly ash needs attention when the MSWI fly ash is used as one of the main raw materials to prepare ceramsite. [ABSTRACT FROM AUTHOR]

In this research, high strength ceramsite was sintered by zinc contaminated soil and red mud. In addition, the influence of sintering temperature and red mud addition on ceramsite properties and Zn immobilization were investigated, and the Zn immobilization mechanisms were determined. The X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM-EDS), and BCR sequential extraction technique were used to determine the crystal phases, microstructures, and Zn immobilization. Under the optimum synthesis conditions (sintering temperature of 1150 °C and the red mud addition of 5%), the sintered ceramsite exhibited a Zn loss rate of 10.31%, Zn leaching concentration of 0.13 mg/L (performed by rotating vibration device), bulk density of 1052.6 kg/m3, 1 h water absorption of 1.06%, and cylindrical compressive strength of 27.06 MPa, implying that the ceramsite obtained under this conditions not only meets the Chinese National Standards and has no environmental risk. High temperature and the addition of red mud were beneficial to the immobilization of Zn in ceramsite. The main immobilization mechanism of Zn in ceramsite was the formation of ZnFe x Al 2−x O 4 spinel and the encapsulation of glass phase. Thus, Zn can be immobilized effectively by ceramsite prepared from zinc contaminated soil and red mud at high temperature. [ABSTRACT FROM AUTHOR]