Co-utilization of sewage sludge and brine sludge for the preparation of porous ceramsite: properties, phase transformation and heavy metal immobilization

The co-utilization of multi-source solid waste is a promising approach for sustainable industrial development. This study aims to incorporate Fe-rich sewage sludge, fly ash and brine sludge into sintered ceramsite. With sewage sludge as the predominant constituent, the influence of fly ash and brine sludge as regulatory constituents on the mechanical and physical properties of the sintered ceramsite is investigated, and the mechanism is elucidated through a comprehensive analysis of phase transformation and microstructure. The ceramsite with 90% sewage sludge and 10% fly ash exhibits a particle compressive strength of 7.13 MPa and an apparent density of 1280 kg/m3. The mineral composition of sintered ceramsite is mainly quartz, anorthite, hematite, and pyroxene. The addition of brine sludge promotes the melting of quartz and hematite, leading to increased pyroxene formation and enhanced compressive strength. Adding 15% brine sludge can convert almost all of the hematite into pyroxene, and the specific strength of ceramsite increases from 5.6×10-3 MPa/(kg/m3) to 7.8×10-3 MPa/(kg/m3). Furthermore, the ceramsite made from sewage sludge, fly ash and brine sludge exhibits a minimal risk of heavy metal leaching.