Il recupero di rifiuti industriali e urbani per la valorizzazione del contenuto organico e minerale nel settore dei fertilizzanti seguendo il modello di economia circolare

Numerous industries are increasingly emphasizing sustainability and environmental responsibility, focusing on waste reduction, resource optimization, and the valorization of industrial by-products into valuable materials. Within the mineral fertilizer sector, there remains a significant reliance on non-renewable mineral resources, which are critical for enhancing agricultural productivity. The extraction of commercially valuable minerals, such as phosphorite—classified by the European Union as a Critical Raw Material (CRM)—entails substantial social, environmental, and economic costs. In response, there is growing interest in shifting towards the use of waste materials and developing processes to transform them into valuable products, addressing both resource depletion and environmental concerns. One promising area of investigation is the recovery and utilization of cogeneration ashes generated from biomass incineration for electricity production. These ashes are recognized as potential sources of essential plant nutrients, including potassium, phosphorus, magnesium, and calcium. Moreover, the presence of basic cations in the forms of oxides, hydroxides, and carbonates enhances their efficacy as soil amendments. With global cogeneration biomass ash production estimated at approximately 480 million tons annually, the development of sustainable methods for their valorization and recovery is urgently needed. This thesis aims to investigate the mineralogical and chemical properties of cogeneration ashes to recover nutrients beneficial for plant growth, while simultaneously reducing landfill disposal in accordance with Circular Economy principles. Eight samples of biomass ashes—four fly ashes and four bottom ashes sourced from various cogeneration plants throughout Italy—were characterized using a multi-methodological approach. Chemical, mineralogical, and microstructural analyses, combined with physico-chemical treatments, were employed to evaluate their phytoavailable components, detect the presence of potentially harmful substances, and assess their feasibility as sustainable resources for mineral fertilizer production. This comprehensive characterization assists in identifying optimal treatment methods to ensure safety, enhance agronomic efficiency, refine recycling strategies, and facilitate practical implementation within the fertilizer sector. The results demonstrate considerable physical and chemical variability in both fly and bottom ashes, influenced by factors such as the type of biomass used for combustion (virgin wood vs. treated wood pellets), combustion temperature, and particle size. Chemical analyses reveal significant concentrations of essential plant nutrients, notably K₂O, CaO, and MgO, in all samples. Additionally, leaching tests and mineralogical investigations identify relevant water-soluble mineral phases that may be bioavailable to plants. Furthermore, the implemented physico-chemical treatments effectively reduce heavy metal concentrations below the thresholds established by the European Fertilizing Products Regulation (EU) 2019/1009, which delineates standards for the commercialization of fertilizer products. In parallel, a thorough characterization of these waste materials enables their efficient integration into fertilizer formulations, thereby reducing reliance on non-renewable mineral resources and ensuring compliance with stringent environmental and human health safety criteria. These findings support the development of innovative, waste-based fertilizer products that adhere to environmental standards, promote resource efficiency, and uphold sustainability within the agricultural sector.