Removal of gangue components from low-grade iron ore by hydrothermal treatment

摘要

In the present the study, the hydrothermal removal of gangue components (Si, Al, and P) from iron ore as a means of producing high-grade iron ore from low-grade iron ore (limonite) is investigated. Ores of different types and countries of origin are treated with several kinds of solvents, and the effects of temperature and type of solvent on the extent of gangue removal are rationalized in terms of the chemical and physical compositions of the iron ores used. Relatively good correlation is observed between the Al and P contents of the iron ore specimens used in this study, while the gangue content correlates with the iron content. When the iron ores are treated with distilled water at 16.5 MPa and temperatures up to 350 degrees C, the removal rate is low, irrespective of the type of iron ore. Furthermore, gangue removal by hydrothermal treatment with 1 M NaOH is higher than those when 1 M NaHCO3 and 1 M Na2CO3 solutions are used. The effects of NaOH concentration and temperature on gangue removal by hydrothermal treatment are investigated using 5 M NaOH, and removal rates of 10-91% for Si, 39-70-% for Al, and 38-76% for P are achieved by treatment at 300 degrees C for most of the specimens. In addition, there is good correlation between the removal rates of Al and P by hydrothermal treatment with 5 M NaOH. Although the development of pores by calcination of iron ore positively affects gangue removal at room temperature by NaOH leaching, no such effect is observed for hydrothermal treatment with NaOH up to 350 degrees C. The specific surface areas and pore volumes of the in iron ore specimens decrease after hydrothermal treatment with NaOH. In addition, the alpha-FeOOH observed in the iron ores before hydrothermal treatment with NaOH is transformed to Fe2O3 in the treated samples. These results demonstrate that this method is effective for converting low-grade iron ores into high-grade iron ores with low porosity, low gangue content, and high Fe content (Fe2O3).