Self-combusted Simulation Of Coal Gangues And Influence Of Different Factors On PAHs

Coal gangues are the by-products of coal production activities. Largeamounts of coal gangue self-combusted after accumulated for a long time,producing toxic and harmful polycyclic aromatic hydrocarbons (PAHs), posing arisk to the surrounding atmosphere, soil and groundwater and threateninghuman’s health. Internal factors and external factors influence the formation anddistribution of PAHs yield from coal gangue. In order to research theconcentrations of PAHs in different ranks of coal gangues and ascertain theinfluences of temperature and air flow rate on the formation of PAHs during coalgangue self-combuston, we collected samples in Malan coal mine, Tunlan coalmine, Ximing coal mine and Duerping coal mine in Taiyuan Xishan coalfieldand Gushuyuan coal mine in Jincheng coalfield. A Soxhlet apparatus and HPLCwere used to analysize the amount of PAHs. In addation, simulations ofself-combustion of coal gangue were conducted in laboratory to discovery theinfluence of temperature and air flow rate on the formation of PAHs. The resultsare as following:(1)The distributions of PAHs in various ranks coal gangue are different, butall the gangue content Naphthalene and Benz[a]anthracene, not content Benzo[a]Pyrene and Indeo[1,2,3-cd]Perylene. With the increasing if coal rank,the totally amount and toxicity of PAHs increased first,then decreased. Thebitumite coal gangue with middle-high degree metamorphism has the lagestconcentration of PAHs, whose toxicity is the most serious. Anthracite has theleast amount of PAHs and the toxicity of which is lowest. XMR, TLR and DEPRhave more kinds of PAHs and the percentages of HPAHs are higher.(2)The totally amount and variety of PAHs are large increasing afterself-combustion of coal gangue. Moreover, the distribution of PAHs accord withfractionation effect: LPAHs concentrated in XAD-2resin and dichloromethaneas gas, HPAHs concentrated in residual samples. After self-combustion, thetoxicity becoming more serious and which is higher in lower temperaturecombustion.(3)LPAHs occupied the most yielding from coal gangue self-combustion.During the self-combustion, oxidation process of coal gangue in lowertemperature (≤450℃) produce more PAHs than combustion process in highertemperature. However, in higher temperature, the variety of PAHs is strongerand the percentage of HPAHs is higher.(4) At the lowest air flow rate, the PAHs yield is the most. When the airflow rate is lower, the change of PAHs yields in each temperature is gentle.Tothe contrary, when the air flow rate is higher, the change of PAHs yields in eachtemperature is violent and the amount of PAHs produced in lower temperatureand higher temperature is extremely different. (5)After self-combustion, the concentration of Naphthalene andPhenanthrene largely increased and the LPAHs occupied the most,at the sametime, Nap/PhA>15. All of these indicate indicate a petrogenic source of PAH.