Experimental Study On Iron Extraction And Phosphorus Reduction By Gas-based Reduction Of High-Phosphorus Ooolitic Hematite

With the increasing shortage of domestic available iron ore resources and the rising import price of foreign iron ore,the domestic steel industry is facing huge pressure of supply and demand.Therefore,the development and utilization of some refractory iron ore has become an urgent problem to be solved.As one of the world’s recognized refractory iron ore types,oolitic hematite is abundant and widely distributed.If the effective utilization of the ore can be achieved,the serious imbalance between supply and demand of iron ore in China can be alleviated.In view of the current situation that it has not been effectively developed and utilized,this experiment takes the high-phosphorus oolitic hematite provided by a foreign company as the research object,and studies the chemical composition,mineral composition and dissemination relationship between the minerals of the ore.The thermodynamic software Factsage 7.0 was used to calculate the thermodynamics of the reaction during the reduction process.Through the gas-based reduction-magnetic separation process,the effects of reduction temperature,holding time,alkalinity（with Ca O）,the flow rate of hydrogen,particle size of reduced ore powder,type and amount of dephosphorization agent and magnetic separation intensity on the iron grade,iron recovery rate,phosphorus mass fraction and dephosphorization rate of concentrate after magnetic separation were discussed.The conclusions obtained through research are as follows:（1）The mineralogical study of high-phosphorus oolitic hematite shows that the iron grade of the ore is 46.75%,mainly in the form of hematite.The mass fraction of harmful element phosphorus is as high as 0.92%,mainly in the form of fluorapatite in gangue minerals.Because it is difficult to destroy the oolitic particles formed by the mutual dissemination of iron minerals,oolitic chlorite and quartz,and the dissemination size of each mineral is extremely fine,it is difficult to dissociate the ore.（2）Thermodynamic studies have shown that phosphorus in fluorapatite is easily volatilized in the form of P₂ during the reduction of high-phosphorus oolitic hematite by hydrogen.In the system of Ca₅（PO₄）₃F-Si O₂-Al₂O₃,when the partial pressure of phosphorus-containing gas is 100Pa,the starting temperature of P₂ formation is 1447K.In addition,the Fe O generated in the reduction of iron oxides will react with Si O₂ and Al₂O₃ in the gangue to form compounds such as fayalite and hercynite,while the solid-phase reaction products will be gradually reduced by H₂ to metallic iron,which is easily combined with volatile P₂ to form complex iron-phosphorus compounds.（3）Combined with the phase analysis and microstructure analysis of the reduction products,it can be seen that when the dephosphorization agent is not added,the metal iron particles cannot aggregate and are wrapped with gangue minerals,and the reduction effect is not obvious.After adding dephosphorization agent,the particle size of iron particles gradually increases and aggregates into small balls,the total number of particles gradually decreases,and the proportion of large particles increases.The effect of adding combined dephosphorization agent is obviously better than that of single dephosphorization agent.Under the action of dephosphorization agent,there is a clear boundary between metal iron and gangue minerals.Fe and P can be separated by magnetic separation process.（4）Through the optimization of various process parameters of gas-based reduction-magnetic separation,the optimum process conditions were determined as follows:reduction temperature 1050°C,holding time 90 min,alkalinity 1.2（with Ca O）,H₂ flow rate 200m L/min,reduction ore powder particle size-200 mesh,magnetic field strength1000 Gs,dephosphorization agent Na₂SO₄,Na₂CO₃ total dosage and ratio of 16%and 9:7,respectively.The iron grade of the concentrate was 81.18%,the iron recovery rate was82.35%,the phosphorus mass fraction was 0.23%,and the dephosphorization rate was75 %.