Mineral carbonation, involving reactions of alkaline earth oxides with CO_2, has received great attention, as a potential carbon dioxide sequestration technology. Indeed, once converted into mineral carbonate, CO₂ can be permanently stored in an inert phase. Several studies have been focalized to the utilization of industrial waste as a feedstock and the reuse of some by-products as possible materials for the carbonation reactions. In this work municipal solid waste incineration fly ash and other ashes, as bottom ash, coal fly ash, flue gas desulphurization residues, and silica fume, are stabilized by low-cost technologies. In this context, the CO₂ is used as a raw material to favor the chemical stabilization of the wastes, by taking advantage of the pH reduction. Four different stabilization treatments at room temperature are performed and the carbonation reaction evaluated for three months. The crystalline calcium carbonate phase was quantified by the Rietveld analysis of X-ray diffraction (XRD) patterns. Results highlight that the proposed stabilization strategy promotes CO₂ sequestration, with the formation of different calcium carbonate phases, depending on the wastes. This new sustainable and promising technology can be an alternative to more onerous mineral carbonation processes for the carbon dioxide sequestration.

This review paper reports a detailed characterization of some combustion or incineration residues and by-products produced in a medium-sized city in Northern Italy. The municipal solid waste incineration (MSWI) generates fly ash, which is a toxic waste. Coal fly ash (CFA) and flue gas desulfurization (FGD) derive from the thermoelectric coal plant located in the same city. Along with these ashes, silica fume and rice husk ash are also considered for the stabilization of fly ash based on their amorphous silica content with the aim to convert them into an inert material. The characterization of all the investigated ashes was performed using different techniques: X-ray diffraction, total reflection X-ray fluorescence, scanning electron microscopy, and transmission electron microscopy. The aim of this work is to describe the reuse possibilities that were proposed for these ashes, which were determined also on the basis of their structural properties. Several possible applications of the investigated ashes are proposed, and the most suitable reuse of stabilized fly ash samples seems to be the production of sustainable plastic composites. This paper shows that the reuse of the by-product materials can allow natural resources to be preserved following the principles of a circular economy.

The livestock sector is one of the most important sectors of the agricultural economy due to an increase in the demand for animal protein. This increase generates serious waste disposal concerns and has negative environmental consequences. Furthermore, the food production chain needs phosphorus (P), which is listed as a critical raw material due to its high demand and limited availability in Europe. Manure contains large amounts of P and other elements that may be recycled, in the frame of circular economy and “zero waste” principles, and reused as a by-product for fertilizer production and other applications. This paper focuses on the extraction and recovery of amorphous silica from rice husk poultry litter ash. Two different extraction procedures are proposed and compared, and the obtained silica is characterized. This work shows that amorphous silica can be recovered as an almost pure material rendering the residual ash free of P. It also addresses the possibility of more specific phosphorous extraction procedures via acid leaching.