Widespread quantitative assessment for potential environmental risk of heavy metals in coal gasification slag from China

The large amount of coal gasification slag (CGS) stored and landfilled on the ground poses potential unknown environmental risks of heavy metals. This study revealed the correlation and environmental risk level and its possibilities of various heavy metals in CGS from different slag types to widespread quantitative assessment the potential pollution degree of CGS in China. The results showed that the probability of Pb, As, and Cd content exceeding the screening value in coal gasification fine slag (CGFS) exceeded 50 %, while the probability of Cr content exceeding the screening value in coal gasification coarse slag (CGCS) was 33.33 %. The content and leaching concentration of Zn in CGFS is significantly positively correlated with that of Ni and Cr. The migration risk of Zn is most significant in CGFS, with an average proportion of 32.55 % for the F1 fraction, which is basically equivalent to the proportion for the F4 fraction; And the occurrence probability of Zn with moderate and higher risk levels is 84.21 %, followed by Mn and Cd. The occurrence state of As in CGS is the most stable. The occurrence probability of Cd with moderate and higher ecological risk levels in CGFS is 61.11 %, significantly higher than that in CGCS. The ecological risks in CGS are mainly caused by Cd, As, and Ni. The probability of unacceptable carcinogenic risks occurring in CGCS is 11.11 %, while the health risks from CGFS are usually low. The potential non-carcinogenic risks of CGS are mainly caused by Cr and As, while the carcinogenic risks are mainly caused by Ni and Cr. Overall, the potential environmental risks of some heavy metals (Cd, Zn, Cr, Ni, etc.) in CGS in China and around the world have significant uncertainty and dispersion, especially CGFS. Fortunately, the solidification/stabilization technology of heavy metals provides application potential for the harmless and resource utilization of CGS.