A method of processing a powder comprising ash has steps: (a) combining the powder with sulphuric or phosphoric acid or a mixture thereof; (b) optionally increasing the alkaline earth metal oxide, carbonate and/or hydroxide content of the powder by adding one or more alkaline earth metal oxides, carbonates, hydroxides or mixtures thereof; and (c) mixing and granulating the combination of (b) to form granules, wherein the combination of (a) has a pH of up to 7, and wherein the reaction between the acid and the alkaline earth metal oxide, carbonate and/or hydroxide produces self-curing granules and generates heat which at least partially dries the granules. Granules obtained are used as is or in fertiliser.
