Synergistic recycling of coal gangue/sludge/oyster shell ceramsite for high-efficiency phosphorus recovery from wastewater

In view of water eutrophication and the shortage of phosphorus in agricultural soils, people are urged to seek efficient and economical phosphorus recovery materials. Solid waste, coal gangue, and sludge can cause severe environmental problems. In this study, coal gangue, sludge, and oyster shell were used, with no additional modifier added to prepare ceramsite (CSOC) by high-temperature sintering. The adsorption capacity of CSOC was achieved at 6.16 mg/g, and the kinetics followed a pseudo-second-order model. The characterisation analysis using SEM, XRD, FT-IR, XPS, and TEM revealed that phosphate initially formed hydrogen bonds with the hydroxyl groups on the surface of CSOC through electrostatic attraction, and subsequently combined with free calcium ions to form amorphous calcium phosphate (ACP/DCP). The continuous release of calcium ions eventually led to the rearrangement of the crystal structure into a stable hydroxyapatite (HAP) phase. The dynamic and reuse experiments of CSOC in the bioretention system showed that the TP removal ability of the CSOC system was 95%. The adsorbed saturated CSOC maintained low water solubility and improved the bioavailability of phosphorus. This research addressed the dual challenges of phosphorus pollution and phosphorus shortage, promoting the sustainable development of industrial waste. • CSOC is sintered from solid waste without the need for additional modifiers • CSOC ceramsite addresses phosphorus pollution and the global phosphorus shortage • CSOC serves as an ideal biofilter material for bioretention systems and constructed wetlands • CSOC with high mechanical strength and zero secondary pollution risk • Ca 2 Al 2 SiO 7 is the key crystal phase responsible for phosphorus removal in CSOC