The Study On Migration And Occurrence Modes Of Uranium During Coal Combustion

Coal resources is abundance and have the species of diversity in China.In recent years,in the wake of environmental awareness enhancement,the problem of environmental pollution is also attracted a wide spread attention in the process of coal utilization.Someone also gradually pay more attention to the harm to human body and uranium in coal released to environment.China average content uranium in coal in close to the global average,about 2.33 mg·kg^-1,but part of the coal mining area is highly enriched uranium content.In Yunnan,Guangxi,Guizhou,Sichuan,etc,uranium content in coal is 36.8¹78 mg·kg^-1.It is higher dozens of times than the national average.So to explore the release regularity of uranium and uranium occurrence features in coal combustion,to reduce the uranium in the release rate is particularly important in the process of coal combustion.The essay focuses on the Pingdingshan coal,Ganhe coal and Lincang coal.Firstly,the occurrence of uranium in coal in different temperature and pressure is simulated by thermodynamics equilibrium software.Uranium is mainly combined with elements such as alkali metal?Na?and alkaline-earth metal?Mg,Ca?to generate the corresponding compounds during coal combustion.With the increase of temperature,uranium is mainly exists in forms of oxide(UO_2.33????UO₂?UO₂?uraninite?),and the valence of uranium showed a downward trend.a small amount of UO₃?g?is generate when the temperature above 1700?.Secondly,according to the calculation results,I designed fluidized bed experiments respectively to research uranium in release regularity during coal combustion of air and oxygen enrichment atmosphere.During air combustion the release rate of uranium in coal increased with the experiment temperature increasing,and in oxygen-enriched combustion atmosphere,under 1000?the release rate of uranium decreased with the experiment temperature increasing.Uranium compounds with alkali metal and alkaline earth metal elements generate uranate around 1000?.Respectively to join in three types of CaCO₃,Na₂CO₃,MgCO₃,K₂CO₃ combustion experiments,CaCO₃,Na₂CO₃,MgCO₃ on the release rate of uranium in coal has obvious inhibitory effect,K₂CO₃ in coal had no significant inhibitory effect on the release rate of uranium.By environmental scanning electron microscopy?ESEM?spectroscopy analysis to know Ca element in ash has the greatest effect in the occurrence regularity of uranium,uranium content in the ash increased with the increase of Ca element content increases,the proportional relationship.