Distribution, occurrence, and leachability of typical heavy metals in coal gasification slag

Coal gasification slag (CGS) contains variable amounts of heavy metals, which can negatively impact the environment. The mineral composition, element distribution, occurrence, and leaching characteristics of heavy metals in coal gasification coarse slag (CGCS) and coal gasification fine slag (CGFS) are studied to explain the leaching behavior of heavy metals in CGS. The movable components of heavy metals in CGFS (0.06 %-63.03 %) are significantly higher than those in CGCS (0 %-18.72 %). Leaching Environmental Assessment Framework 1313 data shows that heavy metals Zn, Cr, Cd, As, Pb, Ni, and Cu exhibit high leaching rates at low pH conditions, with Zn leaching concentrations as high as 2.11 mg/L at pH 2. Zn, Cr, and As exhibit obvious amphoteric leaching characteristics, and the leaching concentration of As at high pH (1.34 mg/L) even exceeds that at low pH (1.31 mg/L). Except for Cu, all heavy metals in CGS exceed the class III groundwater standard in some cases. Therefore, evaluation is needed before resource utilization of CGS due to potential leaching of some heavy metals.