A porous iron powder consisting essentially of a reduced iron powder having a specific surface area above 3000 m2/kg. The reduced iron powder is ferric oxide in a hydrogen environment and mechanical fluid bed operating at barometric pressure. The hydrogen environment has a pH2/pH2O ratio above 2.3. The reduced iron powder is ferric oxide produced by roasting of a solution of ferrous chloride. The end-product particle size is between 1 and 45 microns and has an in-vitro dissolution rate of 100% in at most twenty minutes.