Research on arsenic content and its speciation distribution characteristics in overlying coal and fly ash recycling soil

In order to understand the arsenic content and speciation distribution characteristics in overlying coal and fly ash recycling soil,dry land farming soils from Xingren County,Guizhou province were studied in this paper with sequential chemical extraction method.The results shows that the range of soil arsenic level in the researched area is within 15.71-169.55 mg/kg,the fluctuation range is very large.It is closely related with the different content of high arsenic contained coal and fly ash in the soil samples.The maximum value of soil arsenic(169.55 mg/kg)is much higher than the soil environmental background values(15 mg/kg),the world average soil arsenic content(6.0 mg/kg) and soil arsenic average content in China(9.2 mg/kg).The content of arsenic in the control samples is 15.71 mg/kg,which is also slightly higher than the natural background values of arsenic content in the soil.Soil arsenic pollution of the study area has been becoming more serious.It is caused by the higher arsenic content of sandstone and silty sandstone in the study area,as well as wide distribution of overlying coal and a large amount of reused fly ash in the farmland.Soil arsenic in this study area mainly exists as residue state(72.16%),which is followed by sulfide combination state,iron manganese oxide combination state(5.89%),organic state(3.06%),carbonate combination state(2.51%)and water soluble and exchangeable state(0.93%).They can be arranged in order as:residue state arsenicsulfide combination state arseniciron manganese oxide combination state arsenicorganic state arseniccarbonate combination state arsenicwater soluble and exchangeable state arsenic.Although the total soil arsenic content of this area is too high,the arsenic transformation ability in residual state which arsenic mainly exists in is relatively weak.Therefore,its harm to the environment and human health has yet been in discussion.