| 其他摘要 | In this paper, we collected more than 300 nationwide coal samples with uniform sampling means, and determined some elements contents by most advanced analyzed techniques. According the analyzed data, we did some systemic research on 22 environmental sensitive elements and total sulfur in Chinese coals, and gave some important statistic parameters such as ranges, arithmetic and geometric means, median, standard deviation, and confident level (95%), etc.. We also studied on the main modes of their occurrence in coals, and mechanism, effects of reducing them by coal-cleaning techniques.
Based on the study, some conclusions can be drawn:
1. By the comparison with the results from former researchers, it proved that these samples we studied are the good representative for reflecting the distributions and concentrations of elements in Chinese coals. The ranges and means of 13 environmental sensitive elements are closed to the results analyzed by former researchers in more than ten years. We think our analyzed results are more confident and more closed to the real status of average chemical composition of elements in Chinese coals. Moreover, the analytical data of B and Sn are the most representative in China for now.
2. On the base of no deviation, we calculated the confidence interval (95%) for arithmetic and geometric means, and the interval for elements concentration. And by the means of statistic analysis, the real-means calculated on 95% confident level of 11 elements are in the range of our statistic means±11％, and Se has the most deviation of ±20％.
3. The arithmetic mean is one of the most common variables. Different means have much difference when they are selected for statistic analysis. In the paper, we calculated five kinds of different means of 23 elements contents in coals for comparison. We found the means weighted by coal production are most closed to the arithmetic means of all samples. Most elements means weighted by coal reserves are lower than the others, which is associated with good coal quality and large quantity in Western and Northern China.
4. Most elements in Chinese coals have the ranges within the ranges in the Word given by Swaine (1990). Among them, these elements (Cr、Cu、Mn、Mo、Se、Sn、Th、Tl、U、V、F) have the ranges closed to World coals and the elements (As、B、Ba、Be、Cd、Co、Cl、Hg、Ni、Pb、Sb) have the ranges very lower than World coals.
5. In comparison with the arithmetic means of 22 trace elements in main coal resources countries and in World coals given by Swaine (1990), there are 6 elements (B、Co、Cu、Hg、Pb、U) with the means closed to American coals; 4 elements (As、Cd、Sb、Tl) with the means closed to Australian coals; 4 elements (Ba、Cr、Mo、Ni、V) with the means closed to former Soviet Union coals; and 5 elements (Be、Mn、Se、Th、F) have arithmetic means close to World coals.
6. With the coal ranks increasing, no element means have the significant increasing or decreasing. But from the whole levels of elements in coals with different ranks, the lignite, weak glued coals, no glued coals and gas coals have lower enrichment in environmental sensitive elements, and most elements are more enriched in coals with high ranks. The enrichment degrees of elements in the coals with different coal-forming ages and different coal-accumulated areas all show that most elements are mainly enriched in southern coals, and are very lower in northern and northwestern coals with the reserves more than 3/4 of national reserves.
7. By the analysis of correlation between the environmental sensitive elements and ash, main composition of ash, we preliminarily know the main occurrence forms of these elements in Chinese coals. Most elements are combined with clay minerals, pyrite and some sulfides, and no more relations with carbonates.
8. The analysis for reduction rates of elements during coal cleaning shows that the reduction levels of 15 elements have very significant positive correlation with the reduction levels of ash yields. It proved that in coals most environmental sensitive elements are inorganic forms. So, increasing the coal washing rate can largely decrease the emissions of hazardous elements during coal burning.
9. The reduction rates can be influenced by their occurrence modes, mineral forms, coal ranks and the techniques used by coal-washing plants, so the reduction rates have much difference in different coal samples. In some ones, the reduction rates can come to 70%. From the average, ash, pyritic sulfur and most environmental sensitive elements have the reduction rates between 30% and 70%, and a few with the reduction rates less than 20%. |
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