Removal behaviors of Cu and Pb from heavy metal contaminated silts flushed by citric acid

A range of Pb(II) and Cu(II) contaminated silt columns were prepared to simulate heavy metal contaminated site, and citric acid was employed to flush the silt columns. The concentration of citric acid, flushing time and concentrations of Cu(II) and Pb(II) were considered to study the removal behaviors of heavy metals. The removal efficiency of Cu(II) was found much better than that of Pb(II). The total removal ratio of Cu(II) could reach 59.9-73.4% when using 0.005mol/L citric acid, whereas the removal efficiency decreased with increasing the concentration of citric acid because higher concentration of chelating agent could lead to decrease of permeability in soil. The removal efficiency of Pb(II) was not as good as Cu(II), with the maximum removal ratio only 16.7%, and higher citric acid concentration led to higher removal efficiency, because lower concentration of citric acid could be adsorbed on soil surface and caused inhibitory effect on Pb(II) removing. The removal ratio of Cu(II) was greater when the initial Cu(II) concentration was lower in the contaminated soil, however, the same 0.005 mol/L concentration of citric acid was not effective to remove Pb(II), and the removal behaviors of Cu(II) and Pb(II) from contaminated silts were rather different. Therefore, appropriate concentration of citric acid should be carefully chosen to flush the heavy metal contaminated site, and this study can provide some theoretical basis for remediating heavy metal contaminated site by soil flushing.