Research On Occurrence Form And Migration Behavior Of Mercury In Coal Slime

Mercury is one of the toxic trace elements in environment.A large source of mercury emissions to the environment is from anthropogenic discharge source,it is very important to control the mercury release from anthropogenic discharge source in order to reduce the mercury release in environment.The Hg emission of low calorific value（LCV）coal fired power plant is a new source of anthropogenic discharge of mercury pollution because of the high content mercury in coal slime.However,the shortage of the basic study and the related data of mercury release behavior during coal slime combustion holds back the development of mercury control technology for LCV coal fired power plant.For this purpose,this study focuses on the partitioning behavior of Hg during coal slime combustion.The modes of occurrence of Hg were investigated by using chemical leaching method.And the thermal stability of different forms of mercury were characterized by the temperature programmed decomposition-atomic fluorescence spectroscopy（TPD-AFS）technique.The results show that all the coal slime contain Hcl-soluble Hg,organic-bound Hg,pyrite bound Hg and silicate-bound Hg with different contents.The pyrite-bound Hg is the dominant form of Hg,followed by organic bound mercury,and silicate bound mercury is the least.Part of the pyrite bound mercury is encased in organic matter.The Hcl-soluble Hg releases at a temperature range of 150-450℃,while the pyrite bound mercury at a temperature range of 450-750℃.The silicate bound mercury and organic bound mercury release at temperature ranges of950-1150℃ and 200-450℃.The mercury release characteristics of two coal slimes selected from two coal preparation plants were studied by the temperature programmed decomposition-atomic fluorescence spectroscopy（TPD-AFS）technique.The different thermal treatment conditions of atmosphere,heating rate,and heating temperature were investigated to reveal the Hg transformation mechanism.The results show that the air atmosphere has a positive effect on mercury releasing at lower temperatures,while the amount of Hg⁰release decreases.The specified release temperature ranges for the different modes of occurrence of Hg are scarcely affected by the heating rate of 5,10,and 20℃/min.A higher heating rate could promote the Hg release to some extent.A higher heating temperature could shorten the release time of mercury.A laboratory scale fluidized bed coupled with an on-line analyzing method for mercury was set up to analyze Hg release characterization of coal slimes.The similarities and differences of Hg release behavior as well as the key factors affecting Hg release was investigated to reveal the Hg transformation mechanism during the heat treatment of three coal slimes.The results show that the proportion of Hg⁰released have no relation with temperature at 800℃,900℃ and 1000℃.Under the same temperature,the release proportion of Hg⁰are in the order of N₂>air>O₂.The releasing characterization of Hg⁰for all coal slime during combustion under the same condition is similar.However,the amount and proportion of Hg⁰released is different.The amount of Hg⁰released have close relation with the Hg contents of coal slime and the modes of occurrence of mercury in coal slime play a significant role in the proportion of Hg⁰released.