Characteristics of micro-interface adsorption kinetics between sediments and Cu ions

This work investigates the adsorption of Cu ions in sediments by conducting batch experiments, including isothermal experiments and adsorption kinetics experiments. Data from isothermal experiments were analyzed using the Langmuir, Freundlich and Temkin models, and the experimental kinetic data were fit using pseudo-first-order, pseudo-second-order, Elovich, liquid film diffusion and intra-particle diffusion models. The Langmuir model resulted in the best fit for the equilibrium data, which indicated that the adsorption capacity of Cu ions on the sediment was 1.0403 mg g−1 with a KL value of 4.2877 L mg−1. The Freundlich and Temkin models also provided good fits, and the nF and A values were 3.8565 and 66.9964 L mg−1, respectively, indicating stronger adsorption intensities and adsorption energies between the Cu ions and the sediment. Compared with the pseudo-first-order and Elovich models, the pseudo-second-order model was more appropriate for describing the adsorption kinetics, indicating the chemisorption nature of adsorption. The adsorption kinetic process can be divided into film diffusion, pore diffusion and adsorption reactions. The controlling step for the adsorption kinetics changed with the development of the adsorption process. The entire adsorption process took 180 min. Film diffusion was the controlling step for the first 20 min. During the 20 to 60 min period, the pore diffusion gradually increased and the film diffusion decreased so that both phenomena coexisted. Pore diffusion was the controlling step during the 60-180 min period.