Pilot study of high-phosphorus oolitic iron ore for iron recovery and dephosphorization by direct reduction–magnetic separation
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摘要: 為給回轉窯工業試驗提供參數，以小型試驗最佳結果為基礎，進行了高磷鮞狀鐵礦煤基直接還原?磁選提鐵降磷擴大試驗。結果表明，在最佳的條件下可獲得鐵品位94.17%、鐵回收率77.47%以及磷質量分數0.08%的粉末還原鐵，推薦的回轉窯工業試驗初始條件為：石灰石用量（質量分數）28%、無煙煤用量（質量分數）16%、還原溫度1300 ℃，還原時間3 h。采用XRD以及SEM-EDS研究了無煙煤的作用機理，發現無煙煤用量增加，促進了浮氏體、鎂鐵尖晶石的還原以及鐵顆粒長大，從而提高了鐵的回收效果，但過多的無煙煤通過增強還原氣氛及其帶入的灰分消耗了石灰石，使鐵礦物中的磷以及磷灰石還原成單質磷并與鐵顆粒形成鐵磷合金。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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圖 2 還原焙燒?磁選工藝試驗程序
Figure 2. Experimental procedure for the reduction roasting–magnetic separation process
圖 3 （a）反應（1）~（9）的ΔG與T的關系；（b） 鐵、磷礦物還原與C氣化的平衡圖
Figure 3. (a) Relationship between ΔG and T of reactions (1)–(9); (b) equilibrium diagram of iron and phosphorus mineral reduction and carbon gasification
圖 4 無煙煤用量對粉末還原鐵指標的影響
Figure 4. Effect of anthracite dosages on the indices of powdered reduced iron
圖 5 還原溫度對粉末還原鐵指標的影響
Figure 5. Effect of reduction temperature on the indices of powdered reduced iron
圖 6 還原時間對粉末還原鐵指標的影響
Figure 6. Effect of reduction time on the indices of powdered reduced iron
圖 7 不同無煙煤用量下焙燒礦的XRD圖譜
Figure 7. X-ray diffraction patterns of roasted ores with different anthracite dosages
圖 8 不同無煙煤用量下焙燒礦的SEM圖和EDS分析。（a）16%；（b）18%；（c）20%；（d）圖（a）中點1的能譜圖；（e）圖（b）中點2的能譜圖；（f）圖（c）中點3的能譜圖
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)
圖 9 不同無煙煤用量下磷的遷移行為
Figure 9. Migration behavior of phosphorus under different anthracite dosages
表 1 試樣的化學成分（質量分數）
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 試樣中鐵的物相分析
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 試樣中磷的物相分析
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 粉末還原鐵的化學組成（質量分數）
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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