Migration of lithium, gallium and rare earth elements in coal, coal slime, and coal gangue during combustion

doi:10.11949/0438-1157.20201544

Abstract

Abstract:

Mastering the migration of valuable rare elements in coal during combustion is of great significance to the utilization of valuable elements in coal. Four coal samples with high aluminum content, coal slime, and two coal gangue samples were used in this work. The combine form of lithium (Li), gallium (Ga) and rare earth elements (REE) in these samples was analyzed using a stepwise chemical extraction method. We investigated the escape of Li, Ga, and REE during coal combustion between 300 and 1100℃ and their enrichment behavior in ash. The correlation between migration of rare elements and composition characteristics of coal samples was also discussed. The results showed that Li, Ga and REE in these coal samples were mainly in form of silicate. The escape ratio of these elements during coal combustion was negatively correlated with the ash content in coal, and positively correlated with volatile matter and carbon content. These elements are concentrated in different degrees in ash, and the enrichment efficiency of REE is higher than that of Li and Ga. The higher the content and volatile content of trace elements in the raw materials and the lower the ash content, the higher the content of trace elements in the ash obtained under the same combustion conditions.

Key words: coal combustion, sustainability, waste treatment, valuable rare elements, migration, enrichment

摘要：

掌握煤中伴生有价微量元素在燃烧过程的迁移规律，对伴生元素的利用意义重大。选取4种高铝煤炭、1种煤泥和2种煤矸石等不同组成特性的样品为研究对象，采用逐级化学提取方法分析了锂（Li）、镓（Ga）和稀土（REE）在原料中的赋存形态，考察了以上元素在300~1100℃燃烧过程逸出情况和在燃烧灰中的富集行为，探讨了元素迁移规律与原料组成特性的关联。结果表明，Li、Ga和REE在7种样品中的赋存形态均以硅酸盐态为主，在燃烧过程的逸出率有与原料灰分呈负相关、与挥发分和含碳量呈正相关的趋势。以上元素在灰中均发生了不同程度的富集，REE的富集倍数高于Li和Ga。原料中微量元素含量和挥发分越高、灰分越低，同等燃烧条件下所得灰中微量元素的含量就越高。

关键词: 煤燃烧, 可持续性, 废物处理, 微量稀有元素, 迁移, 富集

CLC Number:

TQ 028.8

MA Zhibin, ZHANG Sen, SHAN Xueyuan, GUO Yanxia, CHENG Fangqin. Migration of lithium, gallium and rare earth elements in coal, coal slime, and coal gangue during combustion[J]. CIESC Journal, 2021, 72(6): 3349-3358.

马志斌, 张森, 单雪媛, 郭彦霞, 程芳琴. 煤、煤泥和煤矸石燃烧过程锂镓稀土元素的迁移规律[J]. 化工学报, 2021, 72(6): 3349-3358.

Figures/Tables 14

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步骤	赋存状态	实验条件
Ⅰ	水溶态	8 g煤样+60 ml去离子水，25℃，24 h
Ⅱ	离子交换态	Ⅰ残渣+60 ml NH₄Ac，25℃，24 h
Ⅲ	有机结合态	Ⅱ残渣+1.47 g/cm³ CHCl₃，40℃干燥漂浮物，650℃灰化，+3 ml HNO₃和3 ml HClO₄，200℃，60 h
Ⅳ	碳酸盐态	Ⅱ残渣，乙醇冲洗，40℃干燥，+20 ml 0.5%HCl
Ⅴ	硅酸盐态	Ⅲ残渣+2.89 g/cm³ CHBr₃，40℃干燥漂浮物，650℃灰化，+3 ml HNO₃和3 ml HF，200℃，60 h
Ⅵ	硫化物态	Ⅲ残渣，水冲洗，40℃干燥，+HNO₃，5 h

步骤	赋存状态	实验条件
Ⅰ	水溶态	8 g煤样+60 ml去离子水，25℃，24 h
Ⅱ	离子交换态	Ⅰ残渣+60 ml NH₄Ac，25℃，24 h
Ⅲ	有机结合态	Ⅱ残渣+1.47 g/cm³ CHCl₃，40℃干燥漂浮物，650℃灰化，+3 ml HNO₃和3 ml HClO₄，200℃，60 h
Ⅳ	碳酸盐态	Ⅱ残渣，乙醇冲洗，40℃干燥，+20 ml 0.5%HCl
Ⅴ	硅酸盐态	Ⅲ残渣+2.89 g/cm³ CHBr₃，40℃干燥漂浮物，650℃灰化，+3 ml HNO₃和3 ml HF，200℃，60 h
Ⅵ	硫化物态	Ⅲ残渣，水冲洗，40℃干燥，+HNO₃，5 h

煤样	工业分析/%(质量, ad)				元素分析/%(质量, ad)
煤样	M_ad	A_ad	V_ad	FC	C	H	N	S
SZ	1.7	23.6	31.4	43.2	79.7	5.1	1.3	1.5
ZGE	3.8	26.9	25.7	43.6	54.9	3.2	1.1	0.4
TKT	4.3	28.7	27.7	39.2	50.3	3.2	0.9	0.9
DT	1.6	27.8	23.3	47.2	49.2	2.9	1.0	0.4
SS	4.3	27.2	36.8	31.6	55.7	3.8	1.2	1.6
XY	1.2	67.5	14.1	17.2	19.5	1.5	0.5	3.8
PS	2.3	70.2	16.2	11.3	12.2	1.8	0.8	2.1

煤样	工业分析/%(质量, ad)				元素分析/%(质量, ad)
煤样	M_ad	A_ad	V_ad	FC	C	H	N	S
SZ	1.7	23.6	31.4	43.2	79.7	5.1	1.3	1.5
ZGE	3.8	26.9	25.7	43.6	54.9	3.2	1.1	0.4
TKT	4.3	28.7	27.7	39.2	50.3	3.2	0.9	0.9
DT	1.6	27.8	23.3	47.2	49.2	2.9	1.0	0.4
SS	4.3	27.2	36.8	31.6	55.7	3.8	1.2	1.6
XY	1.2	67.5	14.1	17.2	19.5	1.5	0.5	3.8
PS	2.3	70.2	16.2	11.3	12.2	1.8	0.8	2.1

815℃ 灰样	化学组成/%（质量）
815℃ 灰样	SiO₂	Al₂O₃	Fe₂O₃	K₂O	CaO	SO₃	MgO	TiO₂
SZ	47.7	42.3	1.8	0.6	3.6	2.2	0.2	1.6
ZGE	44.2	52.3	0.7	0.2	0.8	0.7	0.1	1.0
TKT	49.7	41.2	2.3	0.1	2.9	1.0	0.2	1.4
DT	44.3	41.8	1.9	0.5	4.7	4.3	0.5	2.0
SS	46.5	40.9	4.4	0.6	2.7	3.1	0.4	1.4
XY	51.7	34.0	6.4	1.0	3.5	1.5	0.4	1.3
PS	51.4	41.1	4.5	0.6	0.2	0.5	0.2	1.5