Migration behaviors of arsenic and sulfur from coal during washing process and their release characteristics during combustion process
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摘要: 以宁武煤田两个洗煤厂原煤及洗选产物为研究对象，采用微波消解与氢化物发生-原子荧光光谱相结合方法考察了洗煤过程硫和砷迁移规律，采用砷质量平衡验证的逐级化学提取法探讨了原煤、精煤、矸石、洗中煤和煤泥燃烧后硫和砷形态转化与释放特性及其依赖性。原煤中20%−28%硫和砷迁移至精煤中，46%−61%迁移至矸石中，Pearson相关系数结果表明，样品中无机矿物质是硫和砷迁移的控制因素。精煤中有机硫和砷提高至30%−50%，而矸石中无机硫和砷占比达90%以上，说明原煤及洗选产物中砷与硫赋存形态具有一定相关性。精煤中较多的有机硫和砷在500 ℃以下伴随水分和挥发分析出呈现明显释放特征，矸石中以无机态为主的砷则主要在500−1000 ℃伴随黄铁矿和硫酸盐等矿物质分解与硫一起释放，体现了原煤及洗选产物燃烧时硫与砷释放的同步性。精煤中硫和砷释放速率最快，300和200 s分别达到最大释放率80%−95%和60%−75%；矸石中最慢，300 s时砷达到最大释放率40%−45%，而硫600 s时仍未达最大释放率；洗中煤和原煤介于精煤和矸石之间，样品燃烧时硫和砷赋释放速率差异是由其固有赋存形态差异所致。Abstract: Two raw coals and their washery products were collected from two coal-washing plants of Ningwu coal field, Shanxi, China. The migration behaviors of sulfur (S) and arsenic (As) during coal washing process were investigated by the microwave digestion method together with hydride generation-atomic fluorescence spectrometry. Based on the checked mass balance of As, a sequential-chemical-extraction method was used to explore the dependence between speciation transformation and release characteristics of S and As during the combustion process of raw coal, cleaned coal, coal gangue, middling coal, or coal slime. The results show that 20%–28% of S and As in raw coal are migrated to the cleaned coal, and 46%–61% of them to gangue. Pearson correlation coefficient identifies that the inorganic minerals in samples control the migration behavior of S and As. Compared with the elements in raw coal, the proportions of organic S and As in cleaned coal increase to 30%–50%, while the inorganic S and As in coal gangue account for more than 90%, which indicates the dependence between the species of S and As in raw coal and its washery products. The relatively large amount of organic S and As in the cleaned coal obviously release together with water and volatile matters below 500 ℃. While the inorganic bonded As and S in gangue mainly release during the decomposition process of pyrite, sulfate and other inorganic minerals between 500 and 1000 ℃, which shows the consistency of S and As release characteristics during combustion of raw coal or washery product. The release rates of S and As from the cleaned coal are the fastest among all samples and the corresponding maximum release ratios are 80%–95% at 300 s and 60%–75% at 200 s, respectively, whilst their release rates from gangue are the slowest and As reaches the maximum release ratio of 40%–45% at 300 s but S doesn’t get to the maximum release ratio even at 600 s. The release rates of S and As from the middling coal or raw coal are between the cleaned coal and gangue. The different release rates of S and As during the sample combustion are mainly depended on their speciation distributions in nature.
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Key words:
- coal washing /
- sulfur /
- arsenic /
- migration behavior /
- speciation /
- combustion /
- release characteristics
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图 1 逐级化学提取流程示意图
Figure 1 Schematic diagram of sequential-chemical-extraction procedure
图 3 两个洗煤厂洗煤产物中灰分、硫和砷质量分布
Figure 3 Distribution of ash, sulfur and arsenic in coal washery products from two coal washing plants
（a）: 1# coal washing plant; （b）: 2# coal washing plant
图 4 两个洗煤厂洗选产物中灰分、硫和砷含量相对于原煤的迁移率
Figure 4 Migration rate of ash, sulfur and arsenic in coal washery products relative to raw coal from two coal washing plants
（a）: 1# coal washing plant ; （b）: 2# coal washing plant
图 5 两个洗煤厂样品中砷含量与灰分、硫含量的相关性
Figure 5 Correlation between arsenic content and ash or sulfur content in samples from two coal washing plants
图 6 两个洗煤厂原煤及其洗煤产物中硫和砷形态分布
Figure 6 Speciation distribution of sulfur and arsenic in raw coal and washery products from two coal washing plants
（a）: 1# coal washing plant；（b）: 2# coal washing plant
图 7 两个洗煤厂原煤及其洗煤产物燃烧过程硫和砷释放特性
Figure 7 Release characteristics curves of sulfur and arsenic during combustion process of raw coal and washery products from two coal washing plants
（a）: 1# coal washing plant；（b）: 2# coal washing plant
图 8 两个洗煤厂原煤及其洗选产物不同温度燃烧产物中硫和砷的形态分布
Figure 8 Speciation distribution of sulfur and arsenic in different temperatures combustion products of raw coal and washery products from two coal washing plants
（a）: 1# coal washing plant；（b）: 2# coal washing plant
图 9 两个洗煤厂原煤及其洗选产物中硫和砷1000 ℃恒温燃烧释放特性
Figure 9 Release characteristics curves of sulfur and arsenic during 1000 ℃ isothermal combustion process of raw coal and washery products from two coal washing plants
（a）: 1# coal washing plant；（b）: 2# coal washing plant
表 1 样品的工业分析以及硫和砷含量
Table 1 Proximate analysis, sulfur and arsenic content of samples
Sample Proximate analysis wad/% Sulfur content Arsenic content M A V FC average value
/%RSD
/%average value
/(μg·g−1)RSD
/%Plant 1 Raw coal 1.36 52.74 16.96 28.94 1.37 ± 0.06 4.28 3.97 ± 0.14 3.49 Cleaned coal 1.29 40.23 21.18 37.30 0.82 ± 0.03 3.92 2.31 ± 0.06 2.75 Middling coal 1.37 51.71 17.90 29.02 1.26 ± 0.08 5.99 3.52 ± 0.15 4.31 Coal gangue 1.45 74.79 10.56 13.20 3.06 ± 0.12 4.01 7.08 ± 0.42 5.87 Coal slime 2.40 38.55 20.64 38.41 1.05 ± 0.03 2.87 2.58 ± 0.07 2.84 Plant 2 Raw coal 1.81 45.65 17.19 35.35 2.16 ± 0.07 3.22 3.08 ± 0.08 2.47 Cleaned coal 0.98 34.04 23.01 41.97 1.14 ± 0.04 3.83 2.04 ± 0.07 3.27 Middling coal 1.33 39.47 20.36 38.84 1.67 ± 0.08 4.93 2.63 ± 0.11 4.06 Coal gangue 0.60 79.19 9.08 11.13 6.02 ± 0.32 5.30 7.87 ± 0.45 5.73 Coal slime 1.99 33.68 24.17 40.16 1.23 ± 0.04 3.07 2.85 ± 0.08 2.80 note：ad: air dried basis; RSD: relative standard deviation 
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