A process for the production of iron (III) orthophosphate of the general formula FePO4×nH2O (n≦2.5) comprising: a) producing an aqueous solution containing Fe2+ ions by introducing, iron (II), iron (III) or mixed iron (II, III) compounds selected from hydroxides, oxides, oxide hydroxides, oxide hydrates, carbonates and hydroxide carbonates, together with elementary iron, into a phosphoric acid-bearing aqueous medium, to dissolve Fe2+ ions and to react Fe3+ with elementary Fe in a comproportionation reaction to give Fe2+; b) separating solids from the phosphoric-acid aqueous Fe2+ solution, and c) adding an oxidation agent to the phosphoric-acid aqueous Fe2+ solution to oxidize iron (II) in the solution to precipitate iron (III) orthophosphate of the general formula FePO4×nH2O. The invention includes the product of the process and its use to make LiFePO4 for batteries.