Study on the Preparation of Biochar Ceramsite Based on Sewage Sludge and the Characterization of Its Properties

Biochar ceramsite was prepared from residual sludge at different temperatures. Specific surface area, compressive strength, and toxic leaching tests were used to compare the properties. Through tests and scanning electron microscopy (SEM), it was found that with the increase of preparation temperature, the ceramsite showed higher porosity, larger specific surface area, and better compressive strength. The leaching amount of toxic heavy metals is low when the temperature is higher than 650 °C. According to X-ray diffraction (XRD) analysis, the main component of sludge is quartz. There were amounts of iron and aluminum in sludge, which were the main reason for its good adsorption efficiency. Through the adsorption experiment on Cr(VI), it was found that the adsorption efficiency of the ceramsite on Cr(VI) was better at low pH, and the adsorption isotherm fitted well with Langmuir and Freundlich types. The adsorption process had both monolayer adsorption and multilayer adsorption, and the adsorption process was in line with the pseudo-second-order kinetics.