Preparation of ceramsite from lead-zinc tailings and coal gangue: Physical properties and solidification of heavy metals

Lead-zinc tailings (LZT) are hazardous solid wastes that threaten the environment safety and human health. As a bulk solid waste, coal gangue (CG) also caused pollution. This paper studied the feasibility of using a combination of LZT and CG to produce ceramsite and realizing the solidification of heavy metals. The physical properties of ceramsite were evaluated, and the phase composition and microstructure were analyzed by XRD and SEM-EDS, respectively. The results showed that when the LZT content was <30 wt%, LZT and CG could be used for the preparation of ceramsite, and the prepared ceramsite met the requirements of environmental safety. Proportion of raw materials and sintering temperature affected physical properties of ceramsite. With the increase of LZT content, the apparent density, and the compressive strength of ceramsite first decreased and then increased. The increase of sintering temperature from 1150 °C to 1250 °C reduced the apparent density and the compressive strength of ceramsite. Moreover, the presence of Pb and Zn decreased the apparent density, the compressive strength, and the water absorption of the ceramsite. The valence of Pb and Zn remained as Pb2+ and Zn2+ after the ceramsite sintering. The solidification of ceramsite could be related to chemical effect through the generation of crystals (e.g., Pb3(AsO4)2 and ZnFe2O4) and physical effect though encapsulation. This work provides a potential way to the reduction, recycling, and harmless utilization of LZT and CG.