Described is a method for the manufacture of iron hydroxide, iron oxide hydrate or iron oxide from filter salts from thin acid recovery, in which the filter salts are dissolved in water, the solution is adjusted to a pH of <1, then a pH of 2 to 4 is established by the addition of a strong base, with stirring, the substances precipitating are separated in a known manner, the remanent solution is adjusted to a pH of 6 to 8 by the addition of a strong base, the precipitating iron hydroxide is separated from the solution, washed, dried, and, if desired, dried and/or calcined to form iron oxide.