焚烧飞灰中六价铬化合物碳热还原脱毒

doi:10.11949/0438-1157.20240058

摘要/Abstract

摘要：

碳热还原是垃圾焚烧飞灰中六价铬化合物还原脱毒的有效手段，但碳热还原条件和飞灰的组分变化会影响铬的形态转化。使用竹炭（bamboo charcoal，BC）和粉末活性炭（powered active carbon，PAC）与Na₂CrO₄反应探索碳热还原中Cr(Ⅵ) 形态转化的过程，并分析碳热反应中4种氧化物对Cr(Ⅵ)形态转化的影响。实验结果表明，1000℃以下Na₂CrO₄被还原为NaCrO₂，高于1000℃则转化为Cr₃C₂。氧化物存在时，高于1000℃后Fe₂O₃与被BC还原的铬反应生成FeCr₂O₄，在CaO含量高时转化为CaCr₂O₄；若添加过量BC则仍以Cr₃C₂为主。在喷钙的飞灰中，CaO与被还原的Cr反应生成CaCr₂O₄；若添加过量的BC，Cr(Ⅵ)则被还原为Cr₃C₂。

关键词: Cr(Ⅵ) 还原, 碳热还原, 氧化物, 飞灰, 热力学

Abstract:

Carbothermal reduction is an effective means of reducing and detoxifying hexavalent chromium compounds in waste incineration fly ash, but carbothermal reduction conditions and changes in the composition of the fly ash can affect the speciation transformation of chromium. Bamboo charcoal (BC) and powered active carbon (PAC) were used to react with Na₂CrO₄ to explore the process of carbothermal reduction on the morphological transformation of $C r (Ⅵ)$ , and the effects of four oxides on the morphological transformation of $C r (Ⅵ)$ in the carbothermal reaction were analyzed. The experimental results showed that Na₂CrO₄ was reduced to NaCrO₂ below 1000℃ and converted to Cr₃C₂ above 1000℃. In the presence of oxides, when the temperature was higher than 1000℃, Fe₂O₃ reacted with the chromium reduced by BC to form FeCr₂O₄. When the CaO content was high, it was converted into CaCr₂O₄, if an excessive amount of BC was added, it was still dominated by Cr₃C₂. When trace amounts of BC were added to calcium-sprayed fly ash, the reduced chromium reacted with CaO to form CaCr₂O₄; when excessive amounts of BC were added, Cr(Ⅵ) was reduced to form Cr₃C₂.

Key words: Cr(Ⅵ) reduction, carbothermal reduction, oxides, fly ash, thermodynamics

中图分类号:

X 705

赵国栋, 熊卓, 赵永椿, 张军营. 焚烧飞灰中六价铬化合物碳热还原脱毒[J]. 化工学报, 2024, 75(10): 3730-3741.

Guodong ZHAO, Zhuo XIONG, Yongchun ZHAO, Junying ZHANG. Detoxification of hexavalent chromium compounds in incineration fly ash by carbothermal reduction[J]. CIESC Journal, 2024, 75(10): 3730-3741.

图/表 21

表1 飞灰中4种氧化物的占比

Table 1 Percentage of four oxides in fly ash

飞灰	氧化物占比/%（质量分数）
飞灰	Al₂O₃	SiO₂	CaO	Fe₂O₃
NJ	0.77	2.24	54.55	0.3
XY	0.74	0.66	3.1	0.39
JN	0.936	1.33	22.59	0.689

表2 BC和PAC的化学成分和工业分析

Table 2 Chemical compositions and industrial analysis of BC and PAC

样品	化学成分/%（质量分数）						工业分析/%（质量分数）
样品	SiO₂	MgO	CaO	K₂O	Fe₂O₃	Al₂O₃	M	A	V	FC
BC	12.685	4.032	6.986	47.779	4.461	—	6.28	4.73	14.3	74.69
PAC	23.183	6.722	6.936	2.771	5.993	2.668	4.13	1.23	17.75	76.89

表3 BC和PAC的比表面积

Table 3 Specific surface area of BC and PAC

样品	比表面积/(m²/g)
BC	106.5
PAC	1384.4

表4 热力学计算参数

Table 4 Thermodynamic calculation parameters

样品	SiO₂	Al₂O₃	Fe₂O₃	CaO	Na₂CrO₄	C
P1	1.5	1.5	1.5	1.5	6	2/8
P2	0.9	0.6	0.6	3.9	6	2/8
P3	0.6	0.18	0.12	5.1	6	2/8

图1 实验装置连接示意图

Fig.1 Schematic diagram of the connection of the experimental setup

图2 式（1）~式（8）的Gibbs自由能变化

Fig.2 Gibbs free energy change of Eqs.(1)—(8)

图3 Na2CrO4与C反应的热力学模拟计算

Fig.3 Thermodynamic simulations of the reaction of Na2CrO4 with C

图4 BC/PAC+Na2CrO4在不同保温时间下的XRD谱图

Fig.4 XRD patterns of BC/PAC+Na2CrO4 at different holding times

图5 BC/PAC+Na2CrO4在不同温度下的XRD谱图

Fig.5 XRD patterns of BC/PAC+Na2CrO4 at different temperatures

图6 BC/PAC+Na2CrO4在保温0.5 h和3 h下的XPS谱图

Fig.6 XPS spectra of BC/PAC+Na2CrO4 at holding times of 0.5 h and 3 h

图7 1000℃下BC/PAC+Na2CrO4在不同保温时间下Cr(Ⅵ)的还原率

Fig.7 Reduction rate of Cr(Ⅵ) by BC/PAC+Na2CrO4 at 1000℃ with different holding time

图8 BC与Na2CrO4反应前后的SEM-EDS图像

Fig.8 SEM-EDS images of BC before and after reacting with Na2CrO4

图9 热处理过程中铬的形态变化

Fig.9 Speciation transformation of chromium during heat treatment

图10 式（10）~式（19）的Gibbs自由能变化

Fig.10 Gibbs free energy change for Eqs.(10)—(19)

图11 添加微量竹炭的配灰XRD谱图

Fig.11 XRD patterns of simulated fly ash adding trace BC

图12 添加过量竹炭的配灰XRD谱图

Fig.12 XRD patterns of simulated fly ash with excessive BC addition

图13 3种飞灰添加微量竹炭的XRD谱图

Fig.13 XRD patterns of trace BC added to three types of fly ash

图14 添加微量BC后飞灰中Cr(Ⅵ)的还原率(飞灰∶Na2CrO4∶BC=3∶3∶1)

Fig.14 Reduction rate of Cr(Ⅵ) in fly ash after adding trace BC

图15 3种飞灰添加过量竹炭的XRD谱图

Fig.15 XRD patterns of excess BC added to three types of fly ash

图16 添加过量BC后飞灰中Cr(Ⅵ)的还原率(飞灰∶Na2CrO4∶BC=3∶3∶1)

Fig.16 Reduction rate of Cr(Ⅵ) in fly ash after addition of excess BC

图17 碳热还原过程中铬的形态转化

Fig.17 Speciation transformation of chromium during carbothermal reduction

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