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Oxidation treatment of chromite ores is a commercially applied process for producing mechanically strong pellets for smelting operation in submerged arc furnace. The oxidation behaviour of chromite ores which essentially determines pellet quality bears a strong relationship with ore chemistry, heat treatment, temperature and time. The present study focuses on investigating the relationship between the oxidation behaviours of low FeO Indian chromite ore with process conditions (oxidation temperature and holding time) using a combination of experimental and simulation techniques. Non-isothermal DSC and TG analysis were conducted in temperature range of 100-1100°C to deduce the phase transformations during the oxidation process. In addition, isothermal TG analyses of chromite ores were conducted at 700, 800 and 1000°C with holding time varying between 0 and 180 min. The effect of temperature and time on the phase transformation of chromite spinel to sesquioxide phase was evaluated using XRD, SEM-EDX, and EPMA. Further, thermodynamic calculations were performed using FactSage TM to study the distribution of different elements in chromite and sesquioxide phases during the oxidation process. In addition, kinetic analysis was conducted to investigate the rate controlling phenomena. The results show that phase transformation kinetics are accelerated with increasing temperature and time and 60-120 min oxidation treatment at 1000°C is sufficient to attain equilibrium conditions. The kinetic analysis results in conjunction with experimental oxidation data indicates that phase transformation is both chemical reaction and diffusion controlled.

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The present work demonstrates the extraction of nickel from low-grade chromite overburden by using solid state reduction and direct smelting route. Goethite & Quartz are present as major phases whereas chromite, hematite were identified as minor phases in the mineral. Solid state reduction of pellets were carried out inside a horizontal tube furnace at 1000?C, 1200?C, 1400?C for 30, 60, 90 and 120 minutes respectively with creating reducing atmosphere. Pellets of varying basicity (i.e. 0.5, 0.6, 0.7, 0.8 and 0.9) were used directly in the EAF for smelting studies. Highest percent of nickel (2%) having ~ 91% recovery were obtained in solid state reduction route for pellets which was reduced at 1400?C for 120 minute. Similar recovery (~90%) of nickel was obtained inside the ingot (0.67% Ni ) by using pellets of 0.9 basicity through smelting route. From the present investigation, it could be concluded that the solid state reduction as well as smelting routes are feasible for the recovery of nickel from low grade chromite overburden. The production of nickel pig (low grade ferronickel) could also be feasible by smelting route.