Assessment of Zero Waste Approach by Enhancing Chromium-to-Iron Ratio in Chromite Ore Through Magnetizing Roasting: A Novel Comparative Sustainable Study of Conventional and Hybrid Microwave Heating Methods

In this present study, a techno-economic approach was employed to investigate the enhancement of the chromium-to-iron (Cr/Fe) ratio of chromite ore, utilizing magnetizing roasting via both conventional and microwave heating sources. The primary objective was to selectively remove iron (Fe) from chromite spinel, thereby increasing the magnetic susceptibility of iron-bearing gangue minerals to facilitate their separation within a magnetic field. The alteration of these minerals’ crystalline structure and magnetic properties enabled effective separation through magnetic means. Remarkably, the findings revealed that chromite ore could be significantly upgraded via magnetizing roasting in a hybrid microwave system, achieving an impressive 67.9% recovery rate and a remarkable (Cr/Fe) ratio of 4.77, starting from a Cr/Fe feed ratio of 2.33%. This optimal outcome was attained at a microwave power of 6 kW, a 5 min exposure time, and a reductant dosage of 40%. Similarly, under conventional heating, a (Cr/Fe) ratio of 4.63 was obtained with a recovery rate of 67.34%, with the best results achieved at a roasting temperature of 900 °C, a 60 min roasting time, and a 40wt% reductant dosage. Moreover, the study explored various process variables, including temperature, time, and reductant concentration, using Taguchi statistical design. Characterization of the roasted mass through SEM–EDS analysis and X-ray diffraction confirmed the transformation of hematite into magnetite within the magnetic fraction and the separation of chromite in the non-magnetic fraction. The notable difference in magnetic susceptibility, as verified by vibrating-sample magnetometry (VSM), played a pivotal role in the successful magnetic separation, consistent with XRD and SEM–EDS Elemental mapping data. Intriguingly, the study also highlighted a significant reduction in energy consumption, with a sevenfold decrease in total energy consumption when employing hybrid microwave heating (2.5 kWh) compared to conventional heating (21.25 kWh). These results underscore the substantial potential of microwave magnetizing roasting as a superior and economically viable method for enhancing chromite ore’s (Cr/Fe) ratio.