Preparation of porous ceramsite from municipal sludge and its structure characteristics

In this paper, the municipal sludge was used as the main raw material to prepare a kind of porous ceramsite. The porous ceramsite composition of 50 wt-% of municipal sludge, 10 wt-% of municipal solid waste incineration bottom ash, 45 wt-% of waste glass powders, sintering temperature of 900°C and holding duration of 30 min. The best of the ceramsite synthesised had 1-h water absorption capacity of 51.53%, apparent porosity of 64.14% and pore volume 0.671 mL g⁻¹. During the sintering process, the waste glass powders generated a large amount of liquid phase, wrapt the gas produced by organic matter, and formed a porous structure inside the ceramic particles. At the same time, the silica and aluminium were combined to form Kyanite, which constitutes the basic skeleton of the ceramic particles showing a certain strength. Besides, silicon oxide and calcium silicate generated Wollastonite improving the corrosion resistance of ceramic particles as well. The adsorption capacity of the prepared porous ceramsite modified by acid combined with sodium citrate was 3.1 mg g⁻¹ using the prepared porous ceramsite as substrate. The adsorption kinetics of ammonia nitrogen by porous ceramics conforms to the quasi-second-order kinetic model, and the adsorption isotherm model conforms to the Langmuir model. The findings lay a theoretical foundation for the integration of resource utilisation of solid waste and later application.