Preparation of ultra-lightweight ceramsite from waste materials: Using phosphate tailings as pore-forming agent

To solve the problems of difficult treatment and environmental pollution of regolith granite sand washing sludge (RGSWS1), the study was carried out to prepare ultra-lightweight ceramsite using RGSWS as the main raw material, silica fume as a conditioning agent, red mud as cosolvent, and phosphorus tailings as a pore-foaming agent. The effects of raw meal ratio, sintering temperature (1130–1280 °C), and sintering time (5–25 min) on the properties of ceramsite were investigated. Under the optimal preparation conditions (RGSWS: red mud: silica fume: phosphorus tailings = 60:20:20:10 and sintering at 1220 °C for 15 min). The ceramsite showed a high compressive strength of 2.63 MPa, an expansion rate of 133.7 %, a 1-h water absorption rate of 1.32 %, an apparent density of 792.3 kg/m3, and a bulk density of 349.2 kg/m3. The sintering process transforms the raw meal into substances such as mullite, diopside, and anorthite, which helps to improve the strength of the lightweight ceramsite. At the same time, harmful substances in the raw materials can be effectively solidified in the internal structure of the ceramsite, making the ceramsite have excellent environmental safety. Moreover, the full characterizations have been made to reveal the structure and formation mechanism of ceramsite. This research utilizes four kinds of solid waste to prepare valuable material, which is helpful for the development of environmentally friendly and ultra-lightweight construction materials.