Abstract: A process for manufacturing hardened granules produced by mixing at least fly ash obtained from combustion of a material selected from a coal product and lignite, a binder and water, forming granules of said mixture, hardening said granules in an embedding material at a temperature between 85.degree. and 212.degree. F. by applying heat and separating the hardened granules from the embedding material, said embedding material being used for forming new granules, including the step of embedding the non hardened granules after granulation in a hardening reactor in a fine grained material with a water absorption capacity of at least 8% and being free from a compound generating heat by contacting water, and supplying heat to the mixture of granules and embedding material in said hardening reactor by introducing steam into the mixture of granules and embedding material as present in the hardening reactor to raise and maintain the temperature at a value comprised between 85.degree. F. and 212.degree. F.