Chemical characterization and mobility of metal species in fly ash–water system

The present investigation was conducted to study the leaching characteristics, speciation and fractionation of trace and major elements from fly ash. Five liquid-to-solid ratios (L/S) were selected, ranging from 0.5 to 1. The releasing of trace and major elements from fly ash increased as L/S ratios increased or over time (at pH = 2.88). γ-Al(OH)3, Cd3(PO4)2, azurite, jarosite, MnCO3, Pb(OH)2, quartz (SiO2) and ZnCO3 are the solid phases that control Al, Cd, Cu, Fe, Mn, Pb, Si and Zn activities in fly ash leachates. The sequential chemical extraction tests showed that Al, Cd, Cu, Fe, Mn, Pb, Si and Zn were mainly present in the last three fractions, which were Fe–Mn oxides, organics and residual fractions and their leachability could be well-controlled in common natural environment. According to risk assessment code (RAC); Cd, Cu, Mn and Pb show a medium risk, while Zn and Fe shows low risk level, but Al and Si are considered safe to our environment.