Valorization of Copper Flotation Tailings Leachate into a Magnetic Spinel Product: Effect of Calcination Atmosphere

In the present paper, a route for the simultaneous recovery of Fe, Cu, and Zn from the leaching filtrate of copper flotation tailings through controlled co-precipitation into a single magnetic ferrite-like product is proposed. Unlike conventional sequential recovery of individual metals, the filtrate was used as a combined precursor for substituted magnetite and a Cu–Zn-containing spinel. Across a series of 20 samples, the Fe:(Cu+Zn) molar ratio ranged from 2.05 to 2.47, with a mean value of 2.25, corresponding to the solid-solution region between MFe2O4 and Fe3O4. As the pH increased, iron precipitated first, followed by copper and zinc; at pH 9.5, Fe and Cu were almost completely co-precipitated, while Zn recovery reached approximately 98%. Calcination of the dried precipitate at 600 °C induced crystallization of the spinel phase, consolidation, and partial sintering of the aggregates. A predominantly magnetite-like spinel product was retained under nitrogen, whereas calcination in air resulted in the formation of a substantial hematite fraction. At a magnetic flux density of 1050 mT, the recoveries of the as-dried precipitate, the nitrogen-calcined product, and the air-calcined product were approximately 86%, 96%, and 90%, respectively.