A Combined Soda Sintering and Microwave Reductive Roasting Process of Bauxite Residue for Iron Recovery

In this study an integrated process is presented as a suitable method to transform Fe3+ oxides present in bauxite residue into magnetic oxides and metallic iron through a microwave roasting reduction, avoiding the formation of hercynite (FeAl2O4). In the first step, all the alumina phases were transformed into sodium aluminates by adding sodium carbonate as a flux to BR and then leached out through alkali-leaching to recover alumina. Subsequently, the leaching residue was mixed with carbon and roasted by using a microwave furnace at the optimum conditions. The iron oxide present in the sinter was converted into metallic iron (98%). In addition, hercynite was not detected. The produced cinder was subjected to a wet high intensity magnetic separation process to separate iron from the other elements.

Selective reduction of iron and phosphorus from oolitic ore

Possibility of selective solid-phase reduction of iron from oolitic ore has been experimentally confirmed. Solid phase reduction was carried out at temperatures of 850 and 1000 °C in CO atmosphere and in the mixture with solid carbon. Distribution of iron and phosphorus was investigated with scanning electron microscope. It was found that at temperature of 1000 °C minimum amount of phosphorus (up to 0.3 %) is transformed into the metallic phase at reduction by carbon monoxide. Upon reduction in mixture of ore with carbon, phosphorus content in metal phase reaches 1.0 – 1.3 % evenat temperature of 850 °C. Thermodynamic modeling of the processes occurring during reductive roasting of oolitic ore was carried out depending on temperature (1000 – 1400 K) and amount of carbon in the system. It is shown that reduction temperature and degree of phosphorus reduction vary depending on ratio of CO and CO2 in the gas phase. At temperatures below 892 °C, phosphorus is not reduced and all iron is in metal phase. With an increase in amount of carbon in the system, phosphorus appears in metal phase. With an excess of carbon in the system, all phosphorus is in metal phase at temperature of 892 °С. Thus, with a certain amount of carbon in the system and, correspondingly, with a certain ratio of CO and CO2 in gas phase, selective reduction of iron is possible without phosphorus reduction even at temperature of 1100 °С. Comparison of experimental results with results of thermodynamic calculation confirms possibility of se selective reduction of iron without phosphorus reduction only by carbon monoxide.

Optimization of Microwave Reductive Roasting Process of Bauxite Residue

In this study, microwave-assisted heating is presented as a suitable method to transform the hematite and goethite contained in bauxite residue into magnetite, wüstite, and metallic iron, with a short processing time. The final target was the production of a sinter with strong magnetic properties, allowing the magnetic separation of Fe from the residue. The influence of microwave energy on the sample, the effect of irradiation time, and the carbon/bauxite residue mass ratio (C/BR) were the parameters that have been analyzed to optimize the process. Their optimized combination allowed transforming 79% of the iron present in the sinter into metallic iron. However, hercynite was also formed, and the presence of this mineralogical phase could be considered a possible drawback for its magnetic properties.