Inorganic and organic ligands induced changes in Pb sorption of arid ?clay and calcareous loamy sand soils

The objective of this study was to investigate sorption, desorption, and immobilization of Pb in the clay and calcareous loamy sand soils treated with inorganic ligands (NO₃^?, Cl^? and H₂PO₄^?). Pb sorption was also determined in the presence of oxalate and citrate. The maximum Pb sorption capacities (q) ranged from 42.2 to 47.1 mmol kg^?1 for the clay soil, and from 45.2 to 47.0 mmol kg^?1 for loamy sand soil. It was observed that the binding energy constant (k) for Pb sorbed onto loamy sand soil (528–1061) is higher than that for clay soil (24.38–55.29). The loamy sand soil-sorbed greater quantities of Pb compared to the clay soil when initial pH was ≥ 3. However, it had lower sorption capacity at the lowest initial pH of 2. Additionally, the greatest Pb sorption and immobilization occurred in the soil treated with H₂PO₄. In the clay soil, the sorption of Pb was depressed at 0.1 mol kg^?1 of Cl^?, as compared with other ligands. Concerning organic acids, citrate ligand showed the highest decrease in Pb sorption. It could be concluded that the nature of Pb sorption can depend on the type and quantity of ligands present, as well as the soil type.