Abstract A low temperature method was used to synthesise nanocrystalline zinc ferrite powders from sulphuric pickling water (SPW), a waste product of the steelmaking industry. The synthesis method consisted of coprecipitation of a bi-ionic Fe 3+/Zn 2+ solution with 1M n-butylamine. Fe 3+ from the SPW and Zn 2+ provided by ZnO were mixed at a molar ratio of 2.0. The precursor obtained in this manner showed a 2-line X-ray diffraction pattern similar to that of ferrihydrite. Thermal treatment of the precursor at ∼375 °C led to the formation of pure, fine-particle and stoichiometric ZnFe 2O 4 powders. This process allows the total recovery of the iron in the SPW, as a product of added value. The fine powders were characterised by XRD, FTIR, TG/DSC and SEM. The BET specific surface and the magnetic properties of the powders were also determined.