Abstract This paper presents the results of characterization investigations carried out on the solid residues produced during coal gasification tests performed in the Zecomix (Zero Emission of CarbOn with MIXed technology) research infrastructure. In this pilot-scale plant, coal is gasified in a steam/oxygen-blown bubbling fluidized bed containing olivine. The solid residues, collected both directly from the solid bed (bed ash) and downstream from it (mixed ash), were characterized in terms of their main physical, chemical and mineralogical properties with the aim of identifying suitable management strategies for each of them within the Zecomix process. Thus, an experimental protocol was also developed to separate the organic and inorganic fractions of both ash types. The main constituents of the bed ash were Mg, Si and Fe, which represent the elemental components of olivine. The total organic carbon content of the bulk bed ash was of 5%, while that of the bulk mixed ash proved to be significantly higher (24–27%). Finally, the particle size and density separation procedure developed in this work showed to be effective for separating the organic and inorganic fractions of the bulk samples of both types of residues, allowing to reach separation efficiencies higher than 90%.