Effect of CaO on reducing atmosphere in the direct reduction and magnetic separation process of beach titanomagnetite concentrate
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摘要: 以鐵品位為58.58%、TiO2品位為12.04%的海濱鈦磁鐵礦精礦為試樣，進行煤基直接還原–磁選試驗。從反應產生的CO和CO2氣體組成、總反應的氣化速率、CO分壓值、金屬化率、礦物組成等角度進行分析，查明了CaO在海濱鈦磁鐵礦精礦直接還原?磁選工藝中的作用機理。研究結果表明，CaO可以提高還原劑的氣化速率，促進鈦磁鐵礦的還原，增加CO2氣體的產生量，從而降低CO分壓值。同時發現CaO可以參與固固反應，降低含鈦礦物中的FeO含量，也有利于鈦、鐵組分的遷移和富集，促進金屬鐵顆粒的聚集長大。因此，添加CaO有利于通過磨礦?磁選促進鈦鐵分離與回收。Abstract: The exploitation of refractory iron ores has become increasingly important around the world because of the rapid depletion of easy-to-process iron ores. Ironsand is extensively distributed in the coastal areas of Indonesia, China, and New Zealand, and can provide an alternative to conventional iron ores. Although the composition of ironsand is partially dependent on its location and position, it approximates that of titanomagnetite (Fe3-xTixO4) containing ~ 60% total Fe (TFe). However, the conventional smelting route for smelting beach titanomagnetite concentrate with carbon uses a blast furnace to produce pig iron and titanium slag, which has many disadvantages. First, the smelting process requires lots of coke and a high temperature. Second, sinter blend allows for the addition of only a small amount of beach titanomagnetite concentrate to ensure the desired sintering characteristics. Therefore, in order to efficiently utilize beach titanomagnetite, the processes of direct reduction followed by magnetic separation are generally applied to recover iron. In addition, additives such as CaO, CaCO3, and NaCO3 are often used in the reduction roasting process. These additives may improve the reduction characteristics or facilitate the growth of iron particles to some extent. In order to study the effect of the additive CaO on the direct reduction and magnetic separation of beach titanomagnetite concentrate which contains 58.58% of TFe and 12.04% of TiO2, the mechanisms were investigated by gas composition of CO and CO2, gasification rate of total reaction, CO partial pressure, metallization rate, mineral composition and so on. The results indicate that adding CaO can improve the gasification rate of reductant and facilitate the reduction of titanomagnetite, which improves the generation of CO2 gas and decreases the CO partial pressure. Besides, CaO can participate in solid-solid reaction, reduce FeO content in Ti-containing mineral and facilitate the migration and enrichment of Ti and Fe components, which promote the growth of metallic iron particles. Thus, adding CaO is good for the separation and recovery of Fe and Ti by grinding and magnetic separation.
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圖 2 CO和CO2生成氣體的檢測系統示意圖
Figure 2. Schematic of the system for measuring generated gases of CO and CO2
1—N2 gas cylinder; 2—valves; 3— mass flowmeter; 4—gas analyzer; 5—cooling water; 6—gas inlet; 7—alumina crucible with sample; 8—furnace; 9—filter; 10—scale; 11—thermocouple; 12—exhaust fan
圖 4 添加不同質量分數的CaO對CO2和CO氣體組成的影響。（a）無添加劑；（b）CaO質量分數為2.2%；（c）CaO質量分數為4.4%
Figure 4. Effects of different mass fractions of CaO on the gas composition of CO2 and CO: (a)no addictive; (b) CaO mass fraction, 2.2%; (c) CaO mass fraction, 4.4%
圖 5 添加不同質量分數的CaO對氣化速率和CO分壓值的影響。（a）總反應的氣化速率；（b）CO分壓值
Figure 5. Effects of different mass fractions of CaO on the gasification rate and CO pressure: (a) gasification rate of total reaction; (b) CO partial pressure values
圖 6 添加不同質量分數的CaO對還原樣品的金屬化率影響
Figure 6. Effect of different mass fractions of CaO on the metallization rate of the reduced samples
圖 7 添加不同質量分數的CaO時還原產物的XRD圖譜
Figure 7. XRD patterns of reduced sample with different mass fractions of CaO
圖 8 添加不同質量分數的CaO時還原產物的掃描電鏡圖和EDS分析。（a）無添加劑；（b）CaO的質量分數為4.4%；（c）1點能譜；（d）2點能譜
Figure 8. Morphologies and energy spectra analysis of reduced sample with different mass fractions of CaO: (a) no addictive; (b) CaO mass fraction, 4.4%; (c) EDS spectrum of Point 1; (d) EDS spectrum of Point 2
圖 9 添加不同質量分數的CaO對鐵顆粒平均粒度的影響
Figure 9. Effects of different mass fractions of CaO on the mean size of iron particles
圖 10 添加不同質量分數的CaO對產品指標的影響。（a）還原鐵產品；（b）含鈦產品
Figure 10. Effects of different mass fractions of CaO on product index: (a) direct reduction iron products; (b) titaniferous products
表 1 試樣的化學分析結果
Table 1. Chemical analysis of the sample
% Element Fe TiO2 SiO2 MgO CaO MnO Al2O3 S P Mass fraction 58.58 12.04 1.69 1.74 0.36 0.03 1.23 <0.01 0.02 
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