Mobility of some potentially toxic trace elements in the coal of Guizhou, China

The mobility of 10 potentially toxic trace elements (PTTE), As, Cd, Cr, Cu, Hg, Ni, Pb, Se, Tl, and Zn from 32 coals of the Longtan Group formed in Permian Period in Guizhou Province, China was investigated using sequential extraction procedures. The results demonstrate that PTTEs such as Hg, As, Se, Cd, Cu, and Pb have the highest mobility at surface conditions, and the average extractable fractions of them are 86%, 95%, 79%, 76%, 69%, and 69% of the total amount in coal, respectively. The elements in coal with the lowest leachability include Tl, Cr, and Ni, and the average extractable fractions of them are 30%, 20%, and 29% of the total amount in coal respectively. Zinc has an intermediate behavior, and the average leachable fraction of it accounts for 46% of the total amount in coal. The results demonstrate that mobility of PTTE in coal depends on the speciation of these elements. The elements associated with sulfates, carbonates, sulfides and some organic matter in coal show the highest extraction rates during the weathering process, while elements with silicate affinities are inert at surface conditions.