| Oolitic hematite was one of the complex refractory iron ores in China,and its reserves account for a large proportion.Due to its unique oolitic structure,extremely fine mosaic particle size and closely associated phosphate minerals,it was difficult to obtain good total iron grade,iron recovery rate and dephosphorization effect in the traditional ore dressing process.However,the reduction-magnetic separation method could be used to treat the ore effectively.The iron ore was treated by reduction-magnetic separation method.Reducing agent and dephosphorizing agent were used to reduce iron oxides and phosphate minerals respectively,so as to achieve the purpose of accumulation and enrichment of metallic iron and migration and enrichment of phosphorus.In the subsequent grinding and separation process,reasonable grinding size and magnetic separation intensity were selected to improve the dissociation degree of monomer and the separation efficiency of iron and phosphorus.(1)The reduction of oolitic hematite iron oxide in microwave field was studied.The effect of reduction time and reduction temperature on the metallization rate was explored.The change of iron grain size with reduction temperature was investigated under the condition of reduction time of 20 min.The results showed that the maximum metallization rate reached 92.6% and the maximum grain size of iron reached 53.7 nm at the reduction temperature of 1473 K and reduction time of 20 min.(2)The nucleation growth of oolitic hematite iron grains was studied by microwave heating.Taking the rate of metallization and the size of iron grains as the objects,Avrami-Erofeyev and Kingery-Shikawa two kinds of iron grain nucleation kinetic models were proposed to study the growth mechanism and restrictive links of iron grain nucleation of carbon bearing pellets under various reduction conditions.The results showed that the nucleation growth rate of iron grains was faster in the microwave field,the nucleation rate constant decreased with the increase of temperature,and the growth rate constant increased with the increase of temperature.The nucleation activation energy of iron grains was 51.21 kJ/mol and 18.05 kJ/mol,and the reduction process was controlled by the nucleation of iron grains.The reduction process was controlled by iron grain nucleation.The apparent activation energy of iron grain growth was 55.779 kJ/mol.(3)The change of FeO concentration in the metallized pellets with reduction time and temperature was explored,and the reduction rate was fitted with different kinetic models,and the limiting links in the reduction process were analyzed.The results showed that the whole reduction reaction conforms to Ginstling-Broushtein equation.The apparent activation energy was 11.535 kJ/mol,and the limiting link was gas diffusion.(4)Combined with the published work of the research group,alkalinity agent and dephosphorization agent were added in the preparation of pellets,and microwave heating and low temperature reduction were adopted to obtain reduced pellets with high metallization rate.The effects of grinding size and magnetic separation intensity on iron grade,recovery rate,phosphorus content and dephosphorization rate were explored.The results showed that under the condition of grinding granularity-0.045 mm accounting for 62.90% and magnetic separation intensity of 65 m T,resulting in the iron powder with TFe grade of 87.69%,recovery rate of 77.86%,phosphorus content of 0.30% and dephosphorization rate of 86.37%.The iron grade of oolitic hematite could be increased from 43.50% to 87.69% by reduction-magnetic separation.Under the condition of low temperature reduction,refined iron powder with high iron grade and low phosphorus content could be produced by this process,which was of great significance to alleviate the serious shortage of high-quality iron ore in China's steel industry. |
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