| China is rich in iron ore resources, but most of them are of low grades and refractories, among which high phosphorus oolitic hematite is the typical representative of refractory iron ore resources. High phosphorus oolitic hematite characterizes relatively high content of harmful elements such as P, Al and Si and very fine mineral disseminated granularity, and that after the fine grinding, the materials tend to argillization easily, which make the high phosphorus oolitic hematite the worldwide difficult ore-dressing issue. This thesis, adopting Bayer alkali leaching process, leaches the raw ores of different fineness at about 280℃, and increases the TFe grade of concentrate using magnetic separation and acid leaching tests. The influence of leaching process on the concentrate indicators through the element chemical analysis, X-ray diffraction analysis (XRD), scanning electron microscope (SEM) and EDS spectrum analysis and the basic principle of decreasing aluminum while increasing the iron grade are studied.Through the alkali leaching-high gradient magnetic separation (HGMS) test of ores of different fineness, the results show that the raw ores with different granularities after leaching, the TFe grade of magnetic concentrate and the TFe recovery rate do not vary much with the leaching time, but Al leaching rate roughly presents a trend of rising first and then decreasing. And TFe grade of magnetic concentrate and TFe recovery rate increase along with larger leached granularity. When the leached particle size is -0.074 mm account for 40% of the ore, leaching temperature is 200℃, and leached in the caustic alkali solution with the concentration of 40% for 2h, the TFe grade of magnetic concentrate can be reached to 54.5% and the recovery rate is 81%, while the leached rate of Al is 62% as the periodic indicator. When the addictive (CaO and Na2CO3) is added into the raw ore for the alkali leaching-high gradient magnetic test, the results show that the TFe grade of magnetic concentrate and recovery rate decrease with the increase of addictive amount.The alkali leaching - magnetic concentrate is conducted with acid leaching tests, in which oxalic acid and sulfuric acid are tested for leaching comparison, and the results show that leaching effect with sulfuric acid is better. Leaching test with sulfuric acid of 3% is conducted on alkali leaching - magnetic concentrate with the particle sizes of 0.074 mm and being 40% of raw ores, and when the leaching liquid-solid ratio is 7 and the leaching time is 40 min, the average TFe grade of acid leaching concentrate is above 60%, the average recovery rate is 82%, the average Al leaching rate can reach to 90% and the P grade is around 0.5. Addictive into the alkali leaching-magnetic concentrate of the raw ore is tested, and the results show that addictive alkali leaching has negative influence on acid leaching.Al leaching dynamic tests of raw ores with different granularities is carried out, and the dynamic equations of different granularities during leaching are obtained:The particle size is -0.045mm account for 80% of the raw ore during leaching, r= 4.06×10-6EXP[-25.14×103/RT][OH-]0.5The particle size is -0.074mm account for 80% of the raw ore during leaching, r= 1.07 × 10-5 EXP[-15.46× 103 /RT][OH-]0.75The particle size is -0.074mm account for 60% of the raw ore during leaching, r= 1.94×10-6EXP[-51.27×103/RT][OH-]1.01Through the analysis of chemical composition of samples before and after the leaching and the mineral composition analysis by XRD detection, and SEM detection and EDS spectrum analysis of the samples, the basic principle of leaching process can be speculated as that the alkaline leaching can not leach Al element into the solution, which just destroys the oolitic structure and converts chamosite into aluminum silicate with weaker magnetism and corresponding iron garnet, after the magnetic separation, the aluminum silicates go into tailings, thus Al grade of the concentrate decreases, and TFe grade increases relatively. Acid leaching can dissociate the aluminum silicates attached on the surface of the minerals during the mixing, and at a certain concentration, it can react with apatite in the minerals, thus decreasing the P content in the concentrate. Studies have shown that: Alkaline leaching-magnetic separation-acid leaching process is an effective way which can raise iron grade of high phosphorus oolitic Hematite while reducing Al and P. |
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