Reduction Roasting of High Iron-Bearing Zinc Calcine Under a CO-CO2 Gas: An Investigation of the Chemical and Mineralogical Transformations

The formation of zinc ferrite (ZnFe2O4) during the oxidative roasting of zinc sulfide concentrates can lead to a reduced recovery of zinc during the subsequent zinc treatment process (leaching). To improve zinc recovery in leaching and minimize the environmental aspects influenced by the presence of ZnFe2O4, a selective reduction roasting process is proposed in this study by transforming ZnFe2O4 into ZnO and Fe3O4 under a gaseous atmosphere corresponding to 10% CO and 90% CO2 at between 700 degrees C and 800 degrees C. Accordingly, roasting tests were carried out and the roasted products were characterized by x-ray fluorescence, x-ray diffraction, scanning electron microscopy, laser particle size analysis technique, and vibrating sample magnetometry techniques, as well as by bulk chemical analysis. The results show that the calcine particles grew rapidly in size after roasting at 750 degrees C, and the specific magnetic induction increased from 0.42 emu/g to 11.36 emu/g due to the formation of Fe3O4. After roasting at 800 degrees C, the particles tended to become smaller while the specific magnetic induction dropped to 10.12 emu/g due to the formation of Fe0.85-xZnxO. The remaining part of the zinc present as Fe0.85-xZnxO caused a lower zinc yield in the subsequent leaching process. Therefore, the formation of Fe0.85-xZnxO is the main factor influencing the separation of zinc and iron.