Investigation of Solid-State Carbothermal Reduction of Fayalite with and Without Added Metallic Iron

Copper slag (CS) with Fe-bearing fayalite and magnetite is the main waste generated during the pyrometallurgical processing of metallic copper. In this paper, the solid-state reduction kinetics of fayalite with and without addition of 10 wt.% metallic iron were studied using the isothermal method. The phase transformation of fayalite was verified by x-ray diffraction, scanning electron microscopy, and energy dispersive spectrometer. Results show that the carbothermal reduction of fayalite is controlled by phase boundary reaction (tridimensional shape), and the activation energy decreases from 165.22 kJ mol−1 to 145.74 kJ mol−1 after adding 10 wt.% metallic iron. During the carbothermal reduction process, fayalite decomposes into metallic iron and quartz solid solution, followed by the conversion of quartz solid solution into cristobalite solid solution with increasing temperature. The addition of metallic iron creates a nucleating effect and accelerates the decomposition of fayalite. This work contributes to efforts to optimize the carbothermal reduction of CS.