Pilot study of high-phosphorus oolitic iron ore for iron recovery and dephosphorization by direct reduction–magnetic separation
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摘要: 为给回转窑工业试验提供参数，以小型试验最佳结果为基础，进行了高磷鲕状铁矿煤基直接还原−磁选提铁降磷扩大试验。结果表明，在最佳的条件下可获得铁品位94.17%、铁回收率77.47%以及磷质量分数0.08%的粉末还原铁，推荐的回转窑工业试验初始条件为：石灰石用量（质量分数）28%、无烟煤用量（质量分数）16%、还原温度1300 ℃，还原时间3 h。采用XRD以及SEM-EDS研究了无烟煤的作用机理，发现无烟煤用量增加，促进了浮氏体、镁铁尖晶石的还原以及铁颗粒长大，从而提高了铁的回收效果，但过多的无烟煤通过增强还原气氛及其带入的灰分消耗了石灰石，使铁矿物中的磷以及磷灰石还原成单质磷并与铁颗粒形成铁磷合金。Abstract: With the development of the steel industry, the use of high-grade and easy-to-handle iron ore is gradually decreasing. At present, the effective utilization of low-grade and refractory iron ore, particularly high-phosphorus oolitic iron ore, has gradually become a research hotspot and a worldwide problem. This type of ore is mainly distributed in the USA, France, Germany, Russia, and China and often has an oolitic structure, where the intercalation relationship between iron minerals and gangue minerals is complicated and the phosphorus content is high. Therefore, this type of ore has not yet been developed and utilized. Studies have shown that the use of coal-based direct reduction–magnetic separation to process high-phosphorus oolitic iron ore is one of the methods to achieve efficient utilization of its iron resources. Researchers have conducted in-depth studies on process optimization, dephosphorization mechanism, and iron and phosphorus reduction kinetics. To determine the parameters for the industrial test of the rotary kiln, based on the best result of the small-scale test, a pilot-scale experiment on iron recovery and dephosphorization from high-phosphorus oolitic iron ore was conducted using coal-based direct reduction, followed by magnetic separation. Results showed that under the optimum conditions, the grade and recovery of iron and phosphorus contents in the powdered reduced iron concentrate were 94.17%, 77.47%, and 0.08%, respectively. Limestone dosage of 28%, anthracite dosage of 16%, reduction temperature of 1300 °C and reduction time of 3 h were recommended as the initial conditions for the industrial test of the rotary kiln. The mechanisms of anthracite were investigated by X-ray diffraction and scanning electron microscopy–energy-dispersive X-ray spectroscopy. The results showed that with the increase in anthracite dosage, the reduction of wustite and pleonaste and the growth of iron particles are promoted, thereby improving the recovery effect of iron. However, a high anthracite dosage enhanced the reducing atmosphere and its ash content consumed limestone, causing phosphorus in iron minerals and apatite to be reduced to elemental phosphorus and iron particles to form the iron–phosphorus alloy.
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图 2 还原焙烧−磁选工艺试验程序
Figure 2. Experimental procedure for the reduction roasting–magnetic separation process
图 3 （a）反应（1）~（9）的ΔG与T的关系；（b） 铁、磷矿物还原与C气化的平衡图
Figure 3. (a) Relationship between ΔG and T of reactions (1)–(9); (b) equilibrium diagram of iron and phosphorus mineral reduction and carbon gasification
图 4 无烟煤用量对粉末还原铁指标的影响
Figure 4. Effect of anthracite dosages on the indices of powdered reduced iron
图 5 还原温度对粉末还原铁指标的影响
Figure 5. Effect of reduction temperature on the indices of powdered reduced iron
图 6 还原时间对粉末还原铁指标的影响
Figure 6. Effect of reduction time on the indices of powdered reduced iron
图 7 不同无烟煤用量下焙烧矿的XRD图谱
Figure 7. X-ray diffraction patterns of roasted ores with different anthracite dosages
图 8 不同无烟煤用量下焙烧矿的SEM图和EDS分析。（a）16%；（b）18%；（c）20%；（d）图（a）中点1的能谱图；（e）图（b）中点2的能谱图；（f）图（c）中点3的能谱图
Figure 8. SEM images and EDS analyses of roasted ores with different anthracite dosages: (a) 16%; (b) 18%; (c) 20%; (d) energy spectrum of point 1 in Fig.(a); (e) energy spectrum of point 2 in Fig.(b); (f) energy spectrum of point 3 in Figs.(c)
图 9 不同无烟煤用量下磷的迁移行为
Figure 9. Migration behavior of phosphorus under different anthracite dosages
表 1 试样的化学成分（质量分数）
Table 1. Chemical composition of the sample
% TFe SiO2 Al2O3 CaO MgO K2O P S MnO LOI 55.65 6.71 4.80 2.13 0.37 0.034 0.56 0.016 0.22 4.93 
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表 2 试样中铁的物相分析
Table 2. Distributions of iron in the mineral phases of the sample
Phase Mass fraction of minerals /
%Distribution of iron in minerals/% Magnetite 30.12 54.29 Martite 11.44 20.73 Hematite 13.43 24.14 Siderite 0.43 0.77 Ferrosilite 0.02 0.03 Iron sulfide 0.02 0.04 Total 55.55 100
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表 3 试样中磷的物相分析
Table 3. Distributions of phosphorous in the mineral phases of the sample
Phase Mass fraction of minerals /% Distribution of iron in minerals/% Apatite 0.29 50.88 Phosphorous in the iron-bearing phase 0.24 42.10 Others 0.03 7.02 Total 0.56 100
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表 4 粉末还原铁的化学组成（质量分数）
Table 4. Chemical compositions of the powdered reduced iron
% Fe MFe P CaO SiO2 Al2O3 MgO MnO C S 94.17 92.27 0.080 1.48 1.13 0.64 0.12 0.046 0.49 0.02
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