Influence mechanism of coal gangue / coal fly ash on the sodium reduction roasting reaction of red mud

doi:10.11949/0438-1157.20211588

Abstract

Abstract:

Coal gangue or fly ash and red mud synergistic sodium reduction roasting can realize the form transformation of iron, aluminum, silicon and other elements contained in it, making it easy to separate and recycle. However, a research on the difference of sodium reduction roasting reaction between coal gangue - red mud system and coal fly ash-red mud system has not been reported. In this paper, the influence of atmosphere type, sodium additive amount, roasting temperature and roasting time on the phase composition of the reductive roasted product from coal gangue-red mud and coal fly ash-red mud system was investigated by X-ray diffraction analysis method. In addition, the difference of iron magnetization and aluminum-silicon activation between coal gangue-red mud and coal fly ash-red mud system was analyzed. The results showed that coal gangue-red mud and coal fly ash-red mud systems can simultaneously realize the magnetization of iron-containing phase and the activation of aluminum-silicon phase during the sodium reduction roasting process. The iron-containing phase and the aluminum-silicon phase showed regular changes with the change of sodium additive amount, roasting temperature and roasting time. The sodium additive amount, roasting temperature and roasting time for the coal gangue-red mud system were slightly lower than those for the coal fly ash-red mud system with the same degree of iron magnetization and aluminum-silicon activation. It is mainly related to the occurrence, content and microstructure of reducing substances and aluminosilicate minerals in coal gangue or coal fly ash. This study will provide a theoretical guidance for the feed selecting during the recovery of valuable elements by sodium reduction roasting of coal-based solid wastes (such as coal gangue, coal fly ash) and red mud.

Key words: sintering, activation, reduction, waste treatment

摘要：

煤矸石或粉煤灰与赤泥协同钠化还原焙烧均可实现其所含铁、铝、硅等元素的形态转化，使其易于分离回收；但对于它们分别与赤泥协同钠化还原焙烧反应差异性及机制的研究目前尚未见报道。采用X射线衍射分析方法，分别考察了煤矸石-赤泥、粉煤灰-赤泥体系钠化还原焙烧过程中，气氛类型、钠助剂添加量、焙烧温度、焙烧时间对还原焙烧产物物相组成的影响规律，并对两个反应体系中铁磁化效果及铝硅活化效果的差异性进行分析。结果表明：在钠化还原焙烧过程中，煤矸石-赤泥、粉煤灰-赤泥体系均可同步实现含铁物相的磁化和铝硅物相的活化，且随着钠助剂添加量、焙烧温度、焙烧时间的变化，含铁物相和铝硅物相呈现规律性变化；在相同铁磁化和铝硅活化效果前提下，煤矸石-赤泥体系所需钠助剂添加量、焙烧温度和焙烧时间均略低于粉煤灰-赤泥体系，这主要与煤矸石、粉煤灰中所含还原性物质和铝硅矿物的赋存形态、含量及微观结构有关。研究将为煤矸石、粉煤灰等煤基固废与赤泥协同钠化还原焙烧回收有价元素的原料筛选提供理论指导。

关键词: 烧结, 活化, 还原, 废物处理

CLC Number:

TQ 170.9

Zhiqiang GUO, Kezhou YAN, Jiyuan ZHANG, Dandan LIU, Yangyan GAO, Yanxia GUO. Influence mechanism of coal gangue / coal fly ash on the sodium reduction roasting reaction of red mud[J]. CIESC Journal, 2022, 73(5): 2194-2205.

郭志强, 燕可洲, 张吉元, 柳丹丹, 高阳艳, 郭彦霞. 煤矸石/粉煤灰对赤泥钠化还原焙烧反应的影响机制[J]. 化工学报, 2022, 73(5): 2194-2205.

Figures/Tables 20

Table 1 Chemical compositions of coal gangue， coal fly ash and red mud

物质	Al₂O₃/%	SiO₂/%	CaO/%	Na₂O/%	Fe₂O₃/%	TiO₂/%	MgO/%	K₂O/%	LOI/%	Al/Si
煤矸石	21.06	41.36	0.95	0.43	2.52	0.77	0.50	2.00	23.4	0.61
粉煤灰	29.90	44.40	2.72	0.86	2.67	1.25	0.45	1.50	15.79	0.79
赤泥	27.40	22.40	19.40	9.89	7.81	3.95	0.92	0.81	7.42	1.43

Fig.1 XRD patterns of coal gangue, coal fly ash and red mud

Fig.2 XRD patterns of the sodium roasting products of CG-RM and CFA-RM systems in different atmosphere

Fig.3 XRD patterns of the sodium reduction roasting products of CG-RM and CFA-RM systems with different amount of sodium additive

Fig.4 Relative contents of active phase and magnetic phase in the sodium reduction roasting products of CG-RM and CFA-RM systems with different amount of sodium additives

Fig.5 XRD patterns of the sodium reduction roasting products of CG-RM and CFA-RM systems in different temperature

Fig.6 Relative contents of active phase and magnetic phase in the sodium reduction roasting products of CG-RM and CFA-RM systems in different temperature

Fig.7 XRD patterns of the sodium reduction roasting products of CG-RM and CFA-RM systems at different time

Fig.8 Relative contents of active phase and magnetic phase in the sodium reduction roasting products of CG-RM and CFA-RM systems at different time

Table 2 Difference of optimum experimental conditions for sodium reduction roasting of coal gangue-red mud and coal fly ash-red mud systems

体系	钠铝硅比(mol)	温度/℃	时间/min
煤矸石-赤泥-碳酸钠	1.2∶1∶1	800	90
粉煤灰-赤泥-碳酸钠	1.5∶1∶1	850	150

Table 3 Industrial composition test of coal gangue and coal fly ash

物质	水分/%	灰分/%	挥发分/%	固定碳/%
煤矸石	0.53	75.46	9.07	14.94
粉煤灰	0.17	88.81	1.66	9.36

Fig.9 Raman spectra of coal gangue (a) and coal fly ash (b)

Fig.10 Thermogravimetric diagram of coal gangue (a) and coal fly ash (b)

Fig.11 Crystal structure of kaolinite（a）and mullite（b）

Table 4 Basic crystal structure parameters of kaolinite and mullite

a : 5.148 ?

b : 8.920 ?

c : 14.535 ?

α : 90.000°

β : 100.200°

γ : 90.000°

a : 7.430 ?

b : 7.580 ?

c : 5.740 ?

α : 90.000°

β : 90.000°

γ : 90.000°

Fig.12 Measured XRD patterns of coal gangue and fly ash and simulated XRD patterns of kaolinite and mullite

Fig.13 Energy band structure of kaolinite and mullite

Fig.14 Density of state of kaolinite (a) and mullite (b)

Fig.15 Density of states of Al, Si and O atoms in kaolinite and mullite

Table 5 Average bond length and overlap number of kaolinite and mullite

矿物	键类型	键长/nm	重叠布局数
高岭石	Si—O	1.628	0.535
高岭石	Al—O	2.420	0.0287
莫来石	Si—O	1.624	0.588
莫来石	Al—O	1.837	0.368

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