Mobility and adsorption capacity of Pb and Zn in a polluted soil from a road environment: Laboratory batch experiments

A study of the mobility of lead and zinc in a contaminated soil from a road environment was conducted in order to evaluate the risk of groundwater contamination due to rainwater infiltration. The mobility of trace metals was evaluated using single chemical extractions and single-element sorption experiments. The distribution of trace metallic elements on the various soil fractions investigated with the use of sequential extractions, both before and after single extraction or sorption experiments, enabled the monitoring of changes in their localization. Metals are slightly extracted by sodium chloride solutions. High extraction yield was obtained for lead using EDTA. Lead was removed from the "acid-soluble", "reducible" and "oxidizable" fractions, In contrast, zinc was less dissolved by means of complexation with EDTA, yet it showed very high sensitivity to variations in pH. Following single extractions, metals were redistributed in the "exchangeable" fraction. Sorption experiments evaluated the capacity of the soil to retain additional lead and zinc inputs. The results reveal that pH influences the sorption of these metals and the initial pollution present in the soil may induce desorption phenomena with respect to zinc. The high initial concentrations present in the soil do not seem to prevent the retention of additional metal in significant quantities. Added metals were located in the "exchangeable", "add-soluble" and "reducible" fractions.