Effects of different conditions on Pb2+ adsorption from soil by irrigation of sewage in South China

Pb²⁺ adsorption onto a soil by irrigation of sewage in the Pearl River Delta of South China was examined as a function of the reaction time, solution pH, initial lead concentration, organic matter (humic acid) and competitive ions (Cu²⁺). The adsorption of Pb²⁺ onto the soil was investigated on batch equilibrium adsorption experiments. Results show that the Pb²⁺ adsorption on the soil is relatively rapid in the first 30 min and reaches equilibrium at 2 h, and the kinetics of the adsorption process on the soil is well characterized by the pseudo-second order reaction rate. Langmuir, Freundlich and Temkin isothermal models are fit for the adsorption of Pb²⁺ onto the soil, and the maximum amount of Pb²⁺ adsorption (Q _m) is 7.47 mg/g. The amount of Pb²⁺ adsorption increases with increasing the pH at the range of 1.2–4.5 and reaches a plateau at the range of 4.5–12. The presence of humic acid in soil decreases the adsorption of Pb²⁺ onto the soil at solution pH of 8 since the negatively charged humic acid with Pb²⁺ is difficult to be adsorbed on the negatively charged soil surface. The adsorption of Pb²⁺ onto the soil also decreases in the presence of Cu²⁺ due to the competition adsorption between Pb²⁺ and Cu²⁺.