The Distributions, Modes Of Occurrence And Volatility Of Trace Elements In Coals Of China

The investigation to trace elements in coal has been of importance to coal geology and coal property for decades. In recent years, more attention has been paid to the distributions of trace elements in coals and their mobility during the process of coal mining and utilization, mainly for the concern about the increasing environmental issues. In this doctoral dissertation, the modes of occurrence of about 30 elements and their combination with macerals and minerals in the coals from 10 typical coalfields in China are systematically researched by sink-float tests and petrological methods based on the investigation to the concentration distribution of trace elements in Chinese coals. Moreover, the volatility of trace elements during coal pyrolysis and gasification is explored by means of the experiments of tube furnace carbonization of coals and CO2 reactivity of chars, with the focus on the effects of modes of occurrence of trace elements in coals on their removal features. There are three sections in the dissertation according to the content.Concentration distribution of trace elements in Chinese coalsBased on the systematic measurements of the concentration of 31 elements in 1018 coal samples from 'Chinese coal resource database', the statistics such as arithmetic means, content distribution histogram, etc, are conducted for coals of different ages, regions and classes in China. Using the data of identified coal resources in different districts, the author calculates the weighted average contents of 31 elements in Chinese coals by the introduction of the factor of resource for the first time. The results reveal that there are remarkable differences in the abundance of trace elements in different coals, especially that from different regions. Generally speaking, coals from Upper-Triassic and Upper-Permian in south China have higher content of trace elements, with remarked contrast to that from Lower to Middle-Jurassic in north and northwest China, which usually have relatively lower content of trace elements. At the same time, there is coincidence between the abundance of trace elements in coals from China and all over the world on the whole. The author considers that the pollution of toxic trace elements from coal combustion in China is mainly attributed to the lagged coal utilization technologies, accumulative effects and the singularly enrichment of trace elements in local places.Modes of occurrence of trace elements in coals from representative coalfields in ChinaIt is the core of the dissertation to investigate the modes of occurrence of trace elements in coals from typical coalfields in China. The author explores deeply the 'physical' combination of trace elements in coals, i.e. their distribution in macerals and minerals. In this section, the distributions of trace elements among vitrinite, inertinite and minerals, as well as their organic affinities are calculated by the introduction of Solari method and by the petrological analysis to all fractions obtained in the sink-floatexperiments. Moreover, the differences of enrichments of kaolinite, illite and bauxite on trace elements in coals are emphasized. The results suggest that the modes of occurrence of trace elements are complicated and every element can occur in various forms in different coals. Both the geochemistry of trace elements and maceral composition has remarkable effects on the occurrences of trace elements in coals. The geochemistry of trace elements, especially their activities during weathering processing in exogenic environments, is important to the background value of abundance of trace elements in coals. There are remarkable differences between macerals and minerals on the abilities to enrich trace elements, both in quantity and in kind. On the whole, trace elements are prone to enrichment in illite than in kaolinite in coals. Generally speaking, the higher the organic affinity of element is, the lower its theoretical removal percentage is during coal preparation.Volatility of trace elements during coal pyrolysis and...