Crystal formation and growth by slow cooling for recovery of magnetite particles from copper smelting slag

Copper smelting produces large amounts of slag and new methods of handling this by-product are required. Considering copper smelting slag as metal resource, we studied the effects of a slow cooling process on the crystal growth of magnetite in smelting slag and the applicability of magnetic separation techniques. As the cooling rate was lowered, the weight fraction of magnetite increased together with the average magnetite grain size. Furthermore, slow cooling in an oxidising atmosphere and temperature holding during the slow cooling process promoted magnetite crystal growth. Magnetic separation tests showed that high separation efficiency was possible when the slow cooled slag was ground to a particle size of ≤20 μm owing to the high magnetite liberation ratio. Consequently, slow cooling was shown to effectively promote crystal growth of magnetite and improve magnetic recovery of magnetite. Abbreviations: EDS: Energy dispersive X-ray spectrometer; MLA: Mineral Liberation Analyzer; SEM: Scanning electron microscope; XRD: X-ray diffraction.