Adsorption characteristics of copper (II) ions from aqueous solution onto humic acid-immobilized surfactant-modified zeolite

Humic acid (HA) was immobilized onto surfactant-modified zeolite (SMZ) which was prepared by the loading of cetylpyridinium bromide (CPB) onto natural zeolite. The adsorption behavior of Cu(II) from aqueous solution onto HA-immobilized SMZ (HA-SMZ) was investigated. HA-SMZ exhibited higher adsorption efficiency for Cu(II) than SMZ. The adsorption efficiency of Cu(II) onto HA-SMZ increased with the increase of solution pH from 3 to 7. The adsorption kinetic of Cu(II) onto HA-SMZ was discussed using the pseudo-first-order, pseudo-second-order and intra-particle diffusion models, and the pseudo-second-order model provided the best correlation of the experimental data. The equilibrium adsorption data of Cu(II) onto HA-SMZ were analyzed by the Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models, and the experimental data fitted well with all the isotherm models. Thermodynamic parameters such as Gibbs free energy change, enthalpy change and entropy change were calculated, and the results showed that the adsorption of Cu(II) onto HA-SMZ was feasible, spontaneous and endothermic in nature. The calculated activation energy of adsorption for Arrhenius equation, mean free energy of adsorption for D–R isotherm and Gibbs free energy change showed that the adsorption of Cu(II) onto HA-SMZ not only involves a chemical adsorption process, but also involves an ion exchange process.