Kinetic and Isotherm Studies for Cu²⁺ and Cs⁺ Uptake with Mono- and Bimetallic FeO(OH)-MnOx-Clinoptilolite

This study investigates the adsorption of selected water pollutants, namely caesium and copper, by using natural zeolite of the clinoptilolite type, as well as clinoptilolites coated with MnOx, FeO(OH)-MnOx and FeO(OH). A comprehensive evaluation of these processes was conducted. The kinetics of Cs and Cu adsorption on all examined samples smoothly followed the pseudo-second-order kinetic model, with the liquid film step regarded as the slower step in both cases. The Langmuir isotherm model provided the most accurate description of Cs and Cu adsorption for all examined samples. However, when considering natural clinoptilolite and FeO(OH)-clinoptilolite systems in relation to Cu(II), the Redlich-Peterson model slightly outperformed the Langmuir model. The modification of clinoptilolite with Mn and Fe oxyhydroxides did not significantly enhance the removal efficiency of Cs compared to the unmodified sample. In contrast, the adsorption capacity, especially for MnOx-clinoptilolite, increased fourfold for Cu and other tested cations such as Pb and Zn, indicating improved efficiency in these cases.