Reaction mechanism of CaFe2O4 formation from desulfurized gypsum and Fe2O3 using semi-coke as a reductant

Desulfurized gypsum, a byproduct of industrial processes, can be efficiently recycled through solid-phase reaction to synthesize CaFe 2 O 4 . This study investigates the reaction mechanism of CaFe 2 O 4 formation from CaSO 4 , Fe 2 O 3 , and semi-coke powder using thermodynamic modeling with Factsage 8.3 software. The phase composition and microstructure of the resulting products under varying semi-coke contents and sintering temperatures were characterized using X-ray diffraction (XRD) and scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS). Total Fe and S contents were quantified using inductively coupled plasma optical emission spectroscopy (ICP-OES) and a C/S Analyzer. The results indicate that increasing the semi-coke content from 11.11 wt% to 20.00 wt% leads to an initial rise and subsequent decline in CaFe 2 O 4 yield, while S content exhibits an opposite trend. Similarly, elevating the sintering temperature from 1050°C to 1150°C results in increased CaFe 2 O 4 formation up to 1125°C, beyond which a decrease is observed, alongside a continuous reduction in S content. Optimal synthesis conditions were identified at 15.79 wt% semi-coke and 1125°C, achieving a desulfurization rate of 95.40 % and confirming effective formation of CaFe 2 O 4 . Compared to conventional reducing agents such as coke and C powders, the use of semi-coke enabled a reduction in the required sintering temperature from 1150°C to 1125°C. These results provide a valuable reference for the low-temperature, high-efficiency recycling of desulfurized gypsum into functional ferrite materials.