Iron oxide nanoparticles (goethite and hematite) of various shapes have been synthesized through a simple hydrothermal reaction from the stripped solution of Fe(III) obtained after extraction and separation of Zn and Fe from spent pickle liquor. The influence of pH and synthesis time on the structure and morphology of the as-prepared α-Fe₂O₃ are investigated. It was possible to control the particle size and shape by adjusting the pH (2–12) of the starting solutions and time of synthesis (1–6 h). Under the appropriate conditions, rod-like α-FeOOH (goethite) and hexagonal α-Fe₂O₃ (hematite) materials of the uniform nano-crystalline structure were selectively synthesized in large quantities. The morphology and structure of the final products were investigated in detail by X-ray powder diffraction pattern (XRD), transmission electron microscopy (TEM), Raman spectroscopy and vibrational sample magnetometer (VSM). The probable mechanism of formation of uniform α-FeOOH and α-Fe₂O₃ nano-particles is discussed on the basis of the experimental results and characterization studies. The evaluation of the magnetic property has established the weak ferromagnetism characteristics of both goethite and hematite at room temperature.