Multiscale characterization of borax modified sludge-derived functional ceramsite: Performance, microstructure and environmental risks.

Sludge ceramisites are an important way for harmless treatment and resource utilization of sludge. How to reduce the production energy consumption of sludge ceramisites and minimize the release of HMs has become a key issue in current research. This study used municipal dewatered sludge as raw material, selected borax and wollastonite for co-sintering, and explored the physical and chemical properties, composition and microstructure, nitrogen and phosphorus adsorption characteristics and HMs release characteristics of sludge ceramisites at 900 °C. The results indicated that under lower sintering temperature conditions, sludge ceramisites containing borax (SWB) have good performance characteristics. When the borax content exceeds 8 wt%, it can promote the complete sintering of SWB and help improve the mechanical strength. The water absorption rate, loss rate, and volume loss on ignition rate of SWB can reach 87.1 %-89.3 %, 0.83 %-1.24 %, and 10.81 %-11.73 %, respectively. SWB has high adsorption performance for high concentration phosphate. At the same time, the presence of aluminosilicate glass phase (ASGP) was observed in SWB, which is the main reason why SWB has better mechanical strength than sludge ceramisites without borax (SW). In addition, the ASGP can effectively slow down the leaching of HMs in SWB. Especially, the immobilization effect of Cr is relatively well, and As slightly exceeds the environmental limit. The environmental risk of SWB is extremely low. In summary, SWB exhibited excellent mechanical strength, outstanding water absorption and retention, and extremely low environmental risk, making it an environmentally friendly water treatment material.