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: SO4
2− > 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+ wasmore
noticeable when they contained more NO3
−, Cl− and Ca2+ than SO4
2− 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. |
