A method of processing a powder, comprising (a) contacting the powder with (i) a 2-40% by weight solution of a sulphur- or phosphorous-containing mineral acid or a mixture thereof, or (ii) one or more alkaline earth metal oxides, carbonates or hydroxides, or a mixture thereof; (b) combining the product of (a)(i) with one or more alkaline earth metal oxides, carbonates or hydroxides, or a mixture thereof; or combining the product of (a)(ii) with a 2-40% by weight solution of a sulphur- or phosphorous-containing mineral acid or a mixture thereof and optionally with further of the alkaline earth metal oxides, carbonates or hydroxides, or a mixture thereof; and (c) granulating the combination of (b) to form granules. Phosphate- and potassium-containing fertilisers are made using the granules.
