Research On Mode Of Occurrence And Release Characteristics Of Arsenic

China is a major energy producer and consumer,and is one of the few countries in the world where energy is dominated by coal.As people become more aware of environmental protection,there are some strict controls for conventional pollutants and also some emission requirements for trace elements.Thus,it is vital to study the volatilization of arsenic during coal combustion.Sequential chemical extraction analysis was employed to know the arsenic speciation in coals and its ashes.The results show that arsenic in coal mainly occurs in bound sulfide and residue,while arsenic in ash mainly occurs in residue.No exchangeable arsenic in coal was detected,except for Hongyan coal,while there is a small percentage of exchangeable arsenic in coals.The organic arsenic is unstable and totally evaporated into gaseous form after coal combustion.In addition,the volatilization ratio of arsenic largely depends on the speciation of arsenic in coal,especially the proportion of sulfide-bound and organic arsenic.Steam has a positive effect on characteristics of coal combustion,and with the increase of steam concentration,it does not significantly accelerate coal combustion.The cause is that the gasification between steam and char increases the porosity of char and promotes the coal combustion.The reason is because steam promotes the coal combustion and increases the volatilization of arsenic simultaneously.Similarly,with the further increase of steam concentration,it does not significantly increase the volatilization of arsenic.In addition,temperature is the main factor on arsenic volatilization.With the increase of temperature,the volatilization ratio of arsenic increases gradually,because some high thermal stability arsenic compounds begin to decompose at a relative high temperature.The effect of steam on volatilization of arsenic at 800-1000℃ is more obvious than that at 1100-1300℃.Thermodynamic equilibrium calculations,using HSC Chemistry version 6.0,were performed to study the migration and transformation of arsenic and interactions of arsenic with mineral components.The results show that AsO(g)is the final arsenic speciation despite the oxidizing or reducing atmosphere.Arsenic reacts with mineral to generate arsenates,which are more likely to decompose in reducing atmosphere.