Adsorption and desorption of Cu, Zn, Pb, and Cd on surface sediments from a shallow lake, North China

Abstract

The processes of adsorption and desorption of heavy metal ions on sediments is of great significance for water quality conservation. To investigate the adsorption and release characteristics of heavy metals on sediments from shallow lakes, an isothermal adsorption and desorption experiment of Cu²⁺, Zn²⁺, Pb²⁺, and Cd²⁺ on sediments from Baiyun Lake was carried out. Our results showed that sediments demonstrated a strong capacity of absorbing these heavy metal ions in a sorption system. The maximum sorption capacity for heavy metals on sediments followed the order Pb²⁺> Cd²⁺> Cu²⁺> Zn²⁺. The followed order of the maximum buffer capacities for heavy metals was Pb²⁺ > Cu²⁺ > Zn²⁺ > Cd²⁺. The Langmuir isotherms model can better fit the adsorption of Cu²⁺, whereas the Freundlich isotherm model for the adsorption of Zn²⁺, Pb²⁺, and Cd²⁺. In the maximum initial concentration treatment, Pb exhibited the highest desorption amount, followed by Cu and Zn, whereas the lowest amount of Cd was observed. The exponential and quadratic functions could describe the relationships of adsorption and desorption. In the maximum initial concentration treatment, the adsorption rates of these four heavy metals followed the order Pb²⁺ > Cd²⁺> Cu²⁺> Zn²⁺, whereas the desorption rates followed an opposite order. The hysteresis index (HI) values for Zn was smaller than 1, whereas the HI values for Cu and Cd were slightly larger than 1, suggesting slightly negative hysteresis processes. However, the HI value of Pb was larger than 1, indicating that Pb²⁺ was easily desorbed from sediments.