Study on the adsorption and transport characteristics of Mn(Ⅱ)/Cd(Ⅱ) by sediments in the upper reaches of the Hanjiang River in China

Abstract

Abstract To investigate the pollution characteristics and transformation dynamics of heavy metals in the sediments of the upper reaches of the Hanjiang River, this study conducted a comprehensive study analyzing the adsorption properties and transport mechanisms of Mn(Ⅱ)/Cd(Ⅱ) in these sediments. This was achieved through static and dynamic adsorption experiments, coupled with the application of Hydrus-1D software for detailed analysis. The outcomes of the static adsorption experiments revealed that temperature exerted a minimal influence on the adsorption energy, whereas the pH of the solution significantly impacted it. Both adsorption isotherms and kinetics were employed for fitting the adsorption processes. The results indicated that the adsorption behavior of Mn(Ⅱ)/Cd(Ⅱ) in the sediments aligned more closely with the pseudo-second-order kinetic model. Additionally, intragranular diffusion was found to play a substantial role in the adsorption process. This suggests that the adsorption of Mn(Ⅱ)/Cd(Ⅱ) in the sediments involved a combination of physical and chemical adsorption mechanisms. Furthermore, the dynamic adsorption experiments demonstrated that the initial concentration of heavy metals crucially influenced their migration within the sediments. Characterization results pointed towards ion exchange, complexation reactions, and precipitation reactions as the primary mechanisms driving sediment adsorption of Mn(Ⅱ)/Cd(Ⅱ). Overall, this study research provides enhanced insights into the environmental behavior of these heavy metals and offers valuable guidance for risk assessment related to Mn(Ⅱ)/Cd(Ⅱ) in the sediments of the upper Hanjiang River.