Lightweight aggregates produced from low-temperature sintering of multiple solid wastes for heavy metals removal: Adsorption kinetics and stabilization

Solid wastes, including incinerated sewage sludge ash (ISSA), waste bentonite, and waste glass powder (WGP), were recycled and sintered at a low temperature (680 degrees C) to produce lightweight aggregates (WSA). WGP acted as a fluxing agent to significantly lower sintering temperature of 1000-1200 degrees C in other studies. WSA demonstrated an excellent mechanical strength of 3.76 MPa. The adsorbent dosage, initial pH, kinetics and isotherm on heavy metals adsorption were evaluated in batch adsorption experiments. The isothermal data exhibited a good correlation with the Langmuir model, and the maximum adsorption capacity was approximately 9.26 mg/g at 296 K. Pb(II) removal was dominated by precipitation and cation exchange. Breakthrough curves were determined for fixed-bed adsorption. At 50% breakthrough, the maximum adsorption capacity was 1.82 mg/g. The WSA after heavy metals adsorption were then reused to replace river sand (10-50%) in producing lightweight mortars. The solidification of spent WSA in the lightweight mortars could significantly reduce the leaching of Pb (II) by 98.5%. Moreover, the reuse of spent WSA resulted in low density and low thermal conductivity of cement mortars. This study demonstrates total waste management for municipal solid wastes: upcycling of waste-utilization-permanently stored as construction materials.