In this work, removal of heavy metals (Cr, Mn, Co, Ni, Cu, Zn, As, Cd, and
Pb) from fly ash has been studied using acid leaching and wet oxidation
methods. In parallel, microwave-assisted acid digestion was applied for
determination of pseudo-total concentrations of heavy metals to estimate the
leaching efficiency. Multivariate statistics (Pearson correlation, principal
component analysis, and hierarchical cluster analysis) have shown two
dominant groups of elements, depending on their characteristics and affinity
towards the ash solid phase. Thus, Cr, Zn, Mn, Co, and Ni belong to the
group I, while Pb, As, Cd, and Cu belong to the group II. It was
demonstrated that the wet oxidation method was more suitable than acid
leaching since the reduction in metal concentration was 30 to 75 % compared
to 12 to 25 % obtained by acid digestion. The influence of fly ash treatment
on the residue characteristics was investigated by X-ray diffractometry and
scanning electron microscopy. The analyses revealed surface and structure
changes of fly ash after the wet oxidation treatment. Overall, wet oxidation
could be an appropriate treatment for heavy metal removal from fly ash,
providing a material that could be further used, thus reducing the risk of
pollution caused by the disposal of coal combustion fly ash.