Preparation and characterization of ceramsite from lime mud and coal fly ash

• Lime mud was successfully recycled in the preparation of ceramsites.
• Ceramsite with 5 wt% diatomite and sintered at 1050 °C had the optimal properties.
• High water absorption (39.03%) and compressive strength (4.79 MPa) were obtained.
• Anorthite was the major phase of ceramsites.

Lime mud as a kind of industrial waste has been directly mixed with coal fly ash and different additives (shale, perlite, diatomite and sawdust) to prepare ceramsite by pelletizing and sintering. Effects of the additive, sintering temperature and lime mud content on the physical properties of ceramsite have been analyzed. Crystalline phases and microstructures were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) respectively. After sintering at 1050 °C, ceramsite with 40 wt% lime mud, 55 wt% coal fly ash and 5 wt% diatomite showed the optimal bulk density of 0.74 g/cm3, 24 h-water absorption of 39.03%, apparent porosity of 49.49% and cylinder compressive strength of 4.73 MPa. Anorthite was the major phase of ceramsites, except for ceramsite with 60 wt% lime mud. Ceramsites containing higher calcium (50 and 60 wt% lime mud) showed the existence of gehlenite and wollastonite. Ceramsite with 5 wt% diatomite sintered at 1050 °C also had better crystallization and pores. The reuse of lime mud in the form of ceramsite is an effective way to reduce the solid waste in paper industry.