Study Of New Technique And Mechanism Of Strengthening Limonite's Magnetizing Roasting

In september,2008, our steel industry faced adverse conditions because of the global Subprime Crisis, superadded the three mines continues recently claimed to we should pay as much as 90% more for iron ore unilaterally. The severe domestic and international situation made us realized exploiting refractory iron ore resources had important significance in deeper ways. Limonite and siderite were low-grade and hard-to-win ores, although we had a tremendous amount of them, we had not exerted them effectively for a long time. As a result, it was high time that we should use limonite and siderite reasonably, on this condition, the pressure on our steel industry could be relieved effectively.The grade of raw limonite was 40.33% and the best technological conditions of magnetizing roasting were as follows:magnetizing roasting temperature was 850℃, reducing time was 15min and blending coal proportion was 2%. Upon these conditions, we could get roasted ore which contained 47.15% TFe,2.26 magnetic susceptibility; while the best processconditions of grinding-magnetic separation were:grinding fineness was -0.074mm 87.35% and magnetic density was 61.52kA/m. By magnetic separation process, a concentrate with 60.17% TFe and 64.76% recovery was obtained.The best processconditions of limonite adding siderite by magnetizing roasting were:magnetizing roasting temperature was 850℃, reducing time was 15min and blending coal proportion was 1.4%. On these conditions, we could get roasted ore which contained 47.18% TFe,2.29 magnetic susceptibility; while the best technological conditions of grinding-magnetic separation were as follows:grinding fineness was-0.074mm 86.50% and magnetic density was 61.52kA/m. By magnetic separation process, a concentrate with 61.02% TFe and 70.20% recovery was obtained.The various index sign of limonite adding siderite was better than limonite roasting alone:at the same magnetizing roasting temperature and reducing time, the blending coal proportion decreased from 2% to 1.4% after adding siderite, decrease by 30%; meanwhile the Fe content of magnetic concentrate increased to 61.02% from 60.17%, and the recovery upgraded to 70.20% from 64.76%.By magnetizing roasting of limonite and limonite adding side-rite, the magnetic concentrate we got was so perfect that it could offer a good raw material for next workstage. In the course of mag-netizing roasting, siderite could be self-magnetized, the CO2 came from thermal decomposition could translate FeO into Fe3O4,theFe2O3 was reduced to Fe3O4 under the chemically-formed CO, so thedosage of reducing agent dropped after adding siderite. Meanwhile, because siderite resolved under reducing atmosphere, the decomposetion was: 3FeCO3→Fe3O4+2CO2+CO; the reducing condition not only kept the magnetite stable, not oxy-genated but also the ejective gas CO by resolving could reduce hematite, namely 3Fe2O3+CO→2Fe3O4+ CO2. For these reasons, the Fe content and recovery of magnetic concentrate were better than without siderite.The magnetizing roasting of limonite alone followed unreacted core model, it was controlled by the internal diffusion and its apparent activation energy Ea=34.79KJ/mol while the rate equation was k=0.2227e-4186/T; However, unreacted core model was not applicable to mixed ore,through analyzing and calculating the magnetizing roasting of mixed ore,we got that its apparent activation energy Ea=32.33KJ/mol, meanwhile the rate equation was k= 0.4928e-3888/T.Because of the gas which came from siderite's thermal decomposition wanted to diffuse outwards,the consistency of the mixed ore reduced. At the same time,there were some small opening,as a result,the resistance of gas diffusion dropped,while the reductant dosage also decreased.Most tailings after grinding-magnetic separation was fine-particle mineral, the valuable component Fe was still high, so this paper considered to add some natural coarse-grained magnetite as carrier to recover the valuable element from fine-particle mineral adequately. We found that through calculating: if we wanted to recover the valuable element, the granularity of the magnetic carrier must be equal or less than 100μm, this moment the magnetic agglomeration forces could be the maximum.The best processconditions of magnetic agglomeration test were as follows:natural magnetite's granularity was 120～180μm, the proportion of natural magnetite was 10%, when the grinding fineness was-0.074mm86.50%, we could get magnetic concentrate which had the Fe content 61.81% and recovery 74.85% expect natural magnetite, while the Fe content increased 0.79% and the recovery increased 4.65%.