Chemical associations and sorption capacity of Pb and Zn: column experiments on a polluted soil from the Amizour mining district (Algeria)

The column leaching behavior of lead and zinc is studied on a soil sample from the Amizour-Bejaia mining region, which is one of Algeria's largest natural reserves for Pb and Zn ores. The maximum amount of metal bound to the soil sample after column leaching by a mono-metal solution at pH 7 is 7.0 and 11.3 g/kg for Zn and Pb, respectively. These values exceed the maximum loading capacities derived from previous batch experiments conducted under similar conditions. The studied soil sample displays a stronger affinity for Pb than Zn under the study conditions. These two metals are associated with various chemical fractions of the mine soil sample, as revealed by a five-step, operationally defined sequential chemical extraction procedure (with fractions categorized as: exchangeable, acid extractable, reducible, oxidizable, and residual) following column leaching. After metal addition and sorption, carbonates (i.e. the extractable fraction) and Fe-and/or Mn-(oxy)(hydr)oxide phases (reducible fraction) in the soil sample dominate for both Pb and Zn. The extractable fraction is mainly reserved for the purpose of zinc retention; moreover, the stabilization with Fe-Mn (oxy)(hydr)oxide phases serves as a major carrier for Pb.