Impacts of inorganic ions and temperature on lead adsorption onto variable charge soils

• The adsorption of Pb2 + was greater in the presence of SO42 − than other ions.
• The increase of K+ and Ca2 + concentrations reduced the adsorption of Pb2 +.
• Pb2 + adsorption was more pronounced in the yellow brown soil than in other soils.
• Pb2 + adsorption on soils was more favorable at 5–25 °C than at 35–45 °C.

The effect of inorganic ions and temperature on lead (Pb2 +) adsorption was evaluated on three acidic soils: yellow-brown soil (YBS), latosol soil (LS), and lateritic red soil (LRS). The results showed that the adsorption of Pb2 + in the presence of anions decreased in the order: SO42 − > NO3− = Cl−, while in the presence of cations, it reduced in the order: K+ > Ca2 +. Accordingly, the contamination of YBS, LS and LRS soils with Pb2 + was more noticeable when they contained more NO3−, Cl− and Ca2 + than SO42 − and K+. The distribution coefficient (Kd) of Pb2 + declined in the order: YBS > LS > LRS in the presence of anions. Adsorption and Kd values of Pb2 + were mainly dependent on ion types and altered surface properties caused by the adsorption and/or the formation of ion complexes. The Kd values enhanced slightly with increasing temperature up to 35 °C and then decreased at 45 °C. Based on the thermodynamic parameters, including the heat of reaction (ΔH), entropy change (ΔS) and the free energy change (ΔG), the adsorption process of Pb2 + on YBS, LS and LRS soils was endothermic and impetuous at low temperatures, whereas it was exothermic and non-spontaneous at high temperatures.