Chemical Composition of Ash from Hazelnut (Corylus avellana L.) Biomass Combustion in the Context of Its Potential Reuse in a Circular Economy

The growing importance of renewable energy sources and the implementation of circular economy principles highlight the need for the rational management of biomass combustion by-products. The aim of this study was to assess the chemical composition of ash produced through the combustion of various biomass fractions from four varieties of common hazel (Corylus avellana L.) in the context of its potential for secondary use. The analysis covered the shells, husks, leaves, and shoots of the following varieties: Kataloński, Olbrzymi z Halle, Olga, and Webba Cenny. Combustion was carried out under laboratory conditions at a temperature of 550 °C, and the content of macro- and micro-element oxides (P2O5, K2O, CaO, SO3, Cl, SiO2, MnO, Fe2O3, NiO, CuO) and potentially toxic elements (ZnO, TiO2, Cr2O3) was determined using the EDXRF method. The results showed significant variation in the chemical composition of the ash depending on the biomass fraction and variety. The highest P2O5 content was found in the leaves of the Kataloński variety (5.02), whilst the highest K2O concentration was found in the husk of the Olga variety (47.33%). The maximum CaO content was found in the leaves of the Webba Cenny variety (32.60). The leaf and husk fractions were characterised by the highest content of nutrients of fertilising importance, whilst the shells exhibited the lowest values for most macronutrients. The content of potentially toxic elements was low. The results obtained indicate that the selective utilisation of specific fractions of hazel biomass can increase the efficiency of mineral recovery whilst maintaining environmental safety, in line with the principles of the circular economy.