Leaching Of As, Se And Sb From Coal Gangue And Its Combusted Residue

Since coal has significant economic and environmental benefits, it respected national election has developed rapidly in recent years in China. Due to lack of energy supply, gangue as a low calorific value fuel is regarded as a valuable resource in our country, so generate electricity with combustion gangue is one of ideal useful methods. But a huge amount of by-product coal concentrated in a relatively small coal mining area and its surrounding is mainly used directly as a fuel, so we can not ignore the environmental risks which are brought by its rich harmful elements. At the same time, with more and more gangue used as a fuel for power gengration, the amount of post-combustion ash is increased sharply year by year, and the common method to manage these huge numbers of ash is stacked in the field. Ash in the field is leached by precipitation and immersed by surface and ground water for a long time, and the leached harmful elements pollute our environment and threaten the safety of drinking water, also through ioaccumulation destroy surrounding ecosystems, and even cause serious toxic events.In this thesis, we have selected gangue which were from a coal preparation plant in Pingxiang and its post-combustion bottom ash and fly ash as the research objests, and have used the experiment method of column leaching by setting three different leaching pH (pH=3.67, pH=4.78, pH=7) and two different leaching temperature (0℃,25℃). By1238hours continuous leaching experiments, we have used Atomic Fluorescence Spectrometry determining the leaching solution trace elements of As, Se, Sb and ect. in52sampling time points. Meanwhile, we have researched on the modes of occurrence of As, Se, Sb in three solid samples by the sequential chemical extraction experiment. We have investigated leaching release discipline of As, Se and Sb contained in gangue and post-combustion ash, and also have discussed the environmental risks and geochemical control mechanism of gangue used as fuel in coal mining areas, so we can provide scientific guidance for coal mining area to use effective measures avoiding environmental risks.The experimental results showed that:(1) The cation of leaching solution is primary of Ca. And leaching release of Ca is an important factor to influence and even decide the pH of leaching solution. Since the solubility of Ca(OH)2decreases with increasing temperature, The pH of leaching solution is relatively higher at lower temperatures.(2) At higher pH leaching solutions have higher contents of As, Se and Sb. The accumulated amount of leaching in strongest alkaline leaching solutions of fly ash and bottom ash are largest. But Sb and Se of gangue leaching solutions are largest in the most acidic environment, it may be caused that the leaching solution for etching gangue control the leaching amount of Se and Sb which are uniformly distributed in gangue.(3) Se and Sb in fly ash are easier to leaching than in gangue. As Se and Sb activation after the combustion of gangue, its gravel processing means greater environmental risk.(4) As the greater leaching amount of As, Se and Sb and less precipitation in most area at lower temperatures, it means that the content of leaching solutions is higher and the environmental risk is also greater.(5) Compared to the gangue, As, Se and Sb contented in fly ash enrich obviously, but have slight loss in bottom ash, it is because that volatile As, Se and Sb are easier volatilized to gas and adsorbed and enriched by fly ash during gangue combustion process.(6) In the sequential chemical extraction experiments, we found that the main occurrence mode of As and Sb in gangue is organic form, while As in fly ash is Fe-Mn oxide form and carbonate bounded form. And proportions of water-soluble form and ion-exchange form are all small in the three samples of As, Sb and Se, most less than3%. As in fly ash are easier abstracted than in gangue and bottom ash, Sb in gangue are easier abstracted than in bottom ash and fly ash, but Se is difficult to abstract in these three samples, less than12%.