Arsenic and selenium distribution and speciation in coal and coal combustion by-products from coal-fired power plants

This study investigated arsenic (As) and selenium (Se) distribution and speciation in coal and the burning byproducts (fly ash and gypsum) in five coal-fired power plants in China. Total concentrations of As and Se in coal varied significantly among different power plants, but most of them were below the average As and Se content in Chinese coal. The concentrations of As and Se in fly ash were much higher than that in coal. Total As contents in four gypsum samples were lower than that in coal, while Se contents in four gypsum samples were much higher than that in coal. The species of inorganic As (AsIII and AsV) and Se (SeIV and SeVI) were determined by high-performance liquid chromatography coupled to inductively coupled plasma mass spectrometry after solvent extraction. The extraction efficiencies of As and Se in coal were low, but a considerable amount of As and Se in fly ash and gypsum can be extracted, showing that elements As and Se were easily leached from the burning by-products. Speciation analysis indicated that Se was mostly present as SeIV in all the fly ash and gypsum extracts, and AsV was the dominating species in coal and fly ash extracts. In contrast, AsIII, much more toxic than AsV, was mainly detected in gypsum. Large amounts of coal-fired by-products are produced every year, most of which end up in landfills or stockpiled in the open areas. Our results suggest that the proper disposal of coal-fired solid wastes is urgently demanded.