The Use of Post-Process Raw Materials for the Production of Alkaline Lightweight Aggregates

Waste from the aggregate processing industry has the potential to be used for value-added products. Its plastic properties and sinterability allow for the production of lightweight aggregates. This process can yield materials with high open porosity at various scales. This article presents the possibilities of obtaining lightweight aggregates from clay–silt fractions obtained by washing crushed dolomite aggregates. Aggregate formation was achieved using selected mechanical processing methods, such as dynamic granulation, sedimentation, crushing, and classification. Biomass was added to increase the aggregate’s porosity. The following instrumental techniques were used to assess the aggregate’s parameters: X-ray fluorescence (XRF) to obtain detailed information on the oxide composition of the tested raw materials; high-temperature microscopy (HSM) to determine the specific sintering temperature; and pH and conductivity meters to examine filtration solutions in direct contact with the aggregate. A key issue was to examine the microstructure of the produced aggregates after firing using scanning electron microscopy (SEM), Brunauer–Emmett–Teller method for measuring material surface area (BET), and X-ray diffraction (XRD) technique. The obtained results will allow for further research into developing a concept for the production of lightweight alkaline aggregates. The aggregates produced exhibit high water absorption (approximately 50%), a low bulk density of 0.82 g/cm3, and meso- (approximately 30–100 µm) and bioporosity (approximately 100–500 µm), which is beneficial for the proper development of plant roots and the absorption and release of water. This research contributes to the identification of resources that can be transformed into lightweight aggregates for urban greening, which is consistent with circular economy strategies and environmental protection. The specific mechanisms through which this research supports sustainable development are the reduction in landfill sites and the protection of natural resources. Furthermore, the aggregates produced can form part of blue-green urban infrastructure, which aims to manage rainwater and reduce the urban heat island effect.