The invention relates to an additive mineral for a dietary composition for animals comprising, in a biodigestible form, at least one phosphoric acid salt and a compound capable of forming a salt therewith. The additive is in the form of an aqueous solution in which the salt is in a dissolved state and is provided in the form of phosphate ions and of ions of said compound. The invention also relates to a method for producing the additive and to a device for carrying out this method.