Effect of soil composition on adsorption of lead as reflected by a study on a natural forest soil profile

The adsorption characteristics of lead on each genetic horizon of a natural brown forest soil profile were studied to recognize the possible immobilizing effect of a mineralogical diverse soil profile in the case of a possible lead contamination. Lead adsorption experiments were carried out on whole soil samples, soil clay fractions, as well as on their carbonate and organic matter free variant. TEM-EDS analyses were performed to characterize the adsorption capacity of individual mineral phases. The most important lead adsorbents in order of importance are the organic matter, the clay minerals, and the iron oxides. The most significant process is the ion exchange of calcium by lead with the respect to adsorption. The organic matter adsorbs more lead than clay minerals, and clay fractions adsorb more lead as compared to the whole soil samples. Among mixed layer clay minerals, those containing swelling component have the highest lead adsorption capacity, but the exact distinguishing of the individual clay mineral particles with the respect to their adsorption capacity is not possible. The calcite influences the lead adsorption through its buffering capacity: high calcite content results in lead precipitation. Soils characterized by high amount of organic matter, swelling clay mineral accumulation horizon and calcareous subsoil are suitable medium to immobilize a significant lead pollution.