三类煤阶煤中汞的赋存形态分布特征

Distribution characteristics of mercury speciation in coals with three different ranks

采用逐级化学提取方法与程序升温热解方法研究了两个煤田三类煤阶六个样品中汞的赋存形态及其热稳定性。煤中汞分为可交换态(F1)、碳酸盐+硫酸盐+氧化物结合态(F2)、硅酸盐+硅铝酸盐结合态(F3)、硫化物结合态(F4)和残渣态(F5),其中F2、F4和F5约占煤中汞总量的90%以上,且F4是煤中汞最主要的赋存形态,占比达45.2%～82.1%。煤中汞的赋存形态与煤阶密切相关,随样品煤化程度加深F4的比例显著提高,但F2和F5逐渐降低,其原因可能是汞在煤变质过程中由碳酸盐、硫酸盐或有机物中逐渐迁移至硫化物中。煤中汞的热稳定性依赖于其赋存形态,其中F1热稳定性最差,在150℃以下全部释放;F3热稳定性最强,析出温度在600℃以上;其余三种结合态汞的释放温度界于以上两者之间,依次为F1 <F5 <F2 <F4 <F3;尽可能多地使汞转化为硫化物结合态中较为稳定的形态是煤燃烧及其相关过程液、固副产物中汞稳定化处理的有效方法之一。

The occurrence and thermal stability of mercury in six samples of three coal ranks in two coal fields were studied by stepwise chemical extraction method and temperature programmed pyrolysis method.The results show that mercury in coal can be divided into five fractions:exchangeable mercury(F1),carbonate+sulfate+oxide bound mercury(F2),silicate+aluminosilicate bound mercury(F3),sulfide bound mercury(F4)and residual mercury(F5).Among them,F2,F4 and F5 account for over 90%,especially F4 ranges from 45.2%to 82.1%.Mercury speciation is heavily related to coal rank in this study.The proportion of F4 is significantly increased with increasing the degree of coalification,whilst both F2 and F5 are gradually decreased,which can be inferred that mercury combined with carbonate,sulfate and organic matter transfer to the sulfide during the metamorphic process of coal.The thermal release characteristics of mercury in coal depend on its speciation.F1 has the weakest thermal stability which completely releases when the temperature is lower than 150℃,but F3 is the strongest with the release temperature above 600℃.The release temperature of the other mercury species is between F1 and F3.As a result,the order of release temperature is F1<F5<F2<F4<F3.Based on the above findings,it should be an effective method to transform mercury into much more sulfide with stable state for stabilizing mercury speciation in liquid and solid by-products of coal combustion and other related processes.