The chemical properties of Ba Ba and Sr are very similar, while Ba in coal is isomorphic to K, so it is mostly distributed in clay minerals (Liu Yingjun et al., 1984). Ba is related to silicate minerals, and also closely related to Ca. From the study of British coal, the content of Ba in bituminous coal rich in calcium carbonate is extremely high (above 3,× 1-6), and the study of American bituminous coal also shows that high Ca must be high Ba (Zhang Jun et al., 1999). In addition, Ba also exists in coal in the form of witherite (BaCO3), barite (BaSO4), fibrebonite and some organic phases (Finkelman, 1995). Lindahl et al. (1984) think that the content of Ba decreases with the increase of coal rank, which is caused by the loss of Ba due to the disappearance of organic carboxylic acid functional groups with the increase of coal rank, or it may be because there are more clay minerals in low-rank coal, so more Ba (isomorphic substitution K) enters the mineral lattice than anthracite with low mineral content (Zhao Fenghua, 1997). Although Ba and Ca in the coal in the study area do not show high correlation, they are closely related in cluster analysis, indicating that Ba mainly exists in carbonate minerals.
Co Finkleman(1994) studied 1 coal samples, and thought that 7% ~ 58% of Co in coal could be leached by hydrochloric acid, and this value was higher in low rank coal, and some Co leached by hydrochloric acid existed in the form of complexes in coal. In fact, Co can't be leached by hydrofluoric acid, which means that it has nothing to do with silicate. More than 2% of Co can be leached by nitric acid, which may be related to pyrite. Goldschmidt(1954) thinks that Co can easily enter pyrite structure, especially at high temperature. Cambel et al. (1967) found that 3% ~ 5μ g/g of Co existed in pyrite when studying Czechoslovakian coal. Finkelman(1994) found hundreds of 1-6 Co in UpperFreeport coal by ion probe, and thought that Co in coal existed in sulfide, mainly fine-grained pyrite, and that Co might also exist in clay minerals or be related to organic matter in low-rank coal. Correlation analysis and cluster analysis show that Co mainly occurs in sulfide, followed by clay minerals, and the negative correlation between Cr and ash also shows its organic affinity.
the content of p>Sb in carbonate minerals in nature is extremely low (Liu Yingjun et al., 1984). However, Finkelman(1994) reported Spencer's research results on British coal, and NiSbS crystals were found in carbonate nodules by scanning electron microscope. Xu Qi et al. (199) also believed that there was a positive correlation between Sb and calcite. Finkelman(1994) found very rare and micron-sized minerals (usually sulfides) related to Sb in polished coal by electron probe. When Minkin et al. (1979) studied UpperFreeport coal, it was found that there was a small amount of Sb in sphalerite, which might exist in pyrite solid solution and a small amount of sulfide (stibnite, Sb2S3) dispersed in organic matrix, and some Sb might be related to organic matter. Cluster analysis shows that there is a close relationship between Sb and clay minerals in coal in the study area.
Sn Sn has the triple characteristics of oxygen affinity, iron affinity and sulfur affinity. Ren Deyi and others (1999b) think that Sn in coal is mainly related to clay minerals. Zhuang Xinguo and others (21) believe that Sn in coal exists in the form of sulfur antimony phase, and some of it has affinity with aluminosilicate. Finkelman(1995) thinks that Sn mainly exists in coal in the form of oxides and sulfides. However, there are also many data showing that Sn exists in coal in the form of non-sulfide (Querol et al., 1995; Ren Deyi et al., 1999 b). The content of Sn in coal ash is as high as 5μg/g, and the average content of Sn in plants is 5μg/g/g. Among all kinds of sedimentary rocks, the content in shale rich in organic matter is the highest (Liu Yingjun et al., 1984). This shows that Sn in coal may also be related to organic matter.
Tl Tl is a copper-loving element. Liu Yingjun et al. (1984) thought that the content of Tl in coal can reach 1×1-6, and the content of Tl in sulfide is higher than that in coal itself, because Tl is easy to gather in coal under the reduction condition caused by H2S, so Tl exists in the form of sulfide. Querol et al. (1995) and Spears et al. (1999) also found that Tl in coal mainly exists in pyrite. The high content of Tl in some clay minerals is caused by the adsorption of clay minerals. Zhuang Xinguo et al. (1998) found that there was a good correlation between Tl and Ta in the coal when studying Antaibao 9 coal, which may be caused by adsorption by clay minerals.
Br Br is beneficial to enrichment under the reducing condition rich in organic matter (Liu Yingjun et al., 1984). Many researchers believe that Br in coal mainly exists in organic matter (Mukhopadhyay et al., 1998; Pires et al., 1992; Wang Yunquan et al., 1996b；; Ren Deyi et al., 1999b). Lyons et al. (1989) considered that Br existed in organic components through the study of vitrinite-rich coal. Spears et al. (1999) studied 24 British coal samples, and found that there was a close relationship between Br, Cl and Na, and that Br mainly existed in pore water. Raask(1985) thought that Br and Cl in organic matter existed in halide form, so it was inferred that Br also existed in inorganic form. There is a negative correlation between Br and ash in the coal in the study area. In addition, the abnormal distribution characteristics of Br in the coal seam profile (see chapter 3 for details) all show its strong organic affinity.