Carbon thermal reduction is used to enrich alumina from fly ash and prepare ferrosilicon alloy
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摘要: 在实验室条件下对粉煤灰进行了碳热还原制备硅铁合金并富集氧化铝试验，回收粉煤灰中的Si、Fe、Al等元素。研究发现，反应过程中，当温度升高，生成的硅铁合金中硅的含量随之升高。当配碳量增加，粉煤灰中莫来石相的Al-O-Si键更容易分解，还原成氧化铝和二氧化硅。碳热还原时加入Fe2O3不仅能够降低还原温度，而且莫来石相中的二氧化硅更易被还原成硅，并与金属铁结合生成硅铁合金，这为后续硅铁合金和氧化铝的分离创造了条件。该工艺将粉煤灰、Fe2O3和煤粉以5∶4∶2的质量比进行配料，使用电阻炉在
1600 ℃的条件下进行焙烧，保温2 h后随炉冷却，通过破碎、筛分、研磨、磁选处理还原后的物料，得到硅铁合金初级产品及氧化铝含量较高的尾渣，硅的回收率达到76.44%，铝的实际回收率达到93.96%。Abstract: The comprehensive utilization of fly ash is a solid waste industry with high technical content and application potential, which integrates environmental protection and resource recycling. Ferrosilicon alloy was prepared by carbothermal reduction of fly ash under laboratory conditions and alumina was enriched to recover Si, Fe, Al and other elements in fly ash. It was found that the content of silicon in the ferrosilicon alloy increased with the increase of temperature during the reaction. When the carbon content increases, the Al-O-Si bond of the mullite phase in the fly ash is more easily decomposed and reduced to alumina and silica. The carbothermal reduction is carried out under the condition of adding Fe2O3. After adding Fe2O3, not only the temperature of carbothermal reduction can be reduced, but also the silicon dioxide in mullite phase is easier to be reduced to silicon, and combined with metal iron to form ferrosilicon alloy, which creates conditions for the subsequent separation of ferrosilicon alloy and alumina. In this process, fly ash, iron oxide and pulverized coal are mixed at a mass ratio of 5∶4∶2, and roasted in a resistance furnace at 1 600 °C. After holding for two hours, they are cooled with the furnace. After crushing, screening, grinding and magnetic separation, the reduced materials are treated to obtain ferrosilicon alloy primary products and tailings with high alumina content. The desilication rate reaches 76.44%, and the recovery rate of aluminum reaches 93.96%.-
Key words:
- ferrosilicon /
- aluminum oxid /
- coal fly ash /
- carbon thermal reduction /
- magnetic selection
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图 1 二氧化硅碳热反应的吉布斯自由能
Figure 1. Gibbs free energy diagram of carbothermal reaction of silica
图 2 还原莫来石生成不同硅铁合金的吉布斯自由能
Figure 2. Gibbs free energy in the reduction of mullite to generate different ferrosilicon alloys
图 4 在
1400 ～1600 ℃下粉煤灰碳热还原后物料的XRD图谱Figure 4. XRD pattern of fly ash after carbothermal reduction at 1 400-1 600 ℃
图 5 不同配碳量粉煤灰碳热还原后物料的XRD图谱
Figure 5. XRD patterns of fly ash after carbothermal reduction with different carbon dosages
图 6 不同Fe2O3配加量焙烧后的XRD谱对比
Figure 6. Comparison of XRD spectra after roasting with different additions of Fe2O3
图 7 硅铁合金颗粒的 SEM 形貌及能谱分析
Figure 7. SEM image and EDS analysis of ferrosilicon alloy particles
图 8
1600 ℃条件下配比5∶4∶2焙烧后实物Figure 8. Physical diagram after calcination with a ratio of 5∶4∶2 at
1600 ℃
图 11 磁选后非磁性部分的XRD图谱
Figure 11. XRD pattern of the non-magnetic fraction after magnetic separation
表 1 粉煤灰样品的主要化学组成
Table 1. Main chemical composition of fly ash samples %
SiO2 Al2O3 TFe CaO K2O NaO MgO TiO2 P S MnO 61.85 18.35 4.75 3.37 2.58 1.42 1.60 0.80 0.10 0.34 0.07 
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表 2 硅铁合金颗粒成分
Table 2. Particle composition of ferrosilicon alloy
% Fe Si O Al Ca K Na Mg 63.400 20.910 3.647 0.424 1.342 1.540 0.573 0.637
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表 3 硅铁合金粉末成分
Table 3. Composition of ferrosilicon alloy powder
% Fe Si O Ca Al K Mg Na 53.53 32.53 4.48 2.18 1.15 1.70 0.81 0.59
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表 4 非磁性部分成分
Table 4. Composition of non-magnetic fraction
% Al O Si Ca K Mg Na 其他 35.12 45.85 2.79 4.67 2.69 1.29 1.15 6.44
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