Enhancement of adsorption ability of calcium alginate gel beads towards Pd(II) ion. A kinetic and equilibrium study on hybrid Laponite and Montmorillonite–alginate gel beads

• Calcium alginate–clay beads were used for removing Pd(II) ion from aqueous solution.
• Physico-chemical properties of gel beads were examined by different techniques.
• Montmorillonite and Laponite improve the sorption ability of alginate towards Pd(II).
• Kinetics of Pd(II) adsorption and Ca(II) release by gel beads was studied.
• Sorption quotients were determined by Langmuir and Freundlich isotherm equations.

The adsorption ability of hybrid Montmorillonite and Laponite–calcium alginate gel beads towards Pd2 + ion was studied in the pH range 2–4, in pure water and in aqueous NaCl solution at I = 0.01 mol L− 1 and T = 25 °C. The pseudo second order kinetic equation and the Langmuir and Freundlich isotherms were used to fit the kinetic and thermodynamic experimental data. A comparison of the results already published on the adsorption capacity of calcium alginate gel beads at the same experimental conditions was made. Enhancement of palladium(II) adsorption by alginate beads with the addition of the two clay minerals was obtained, with increments higher than 50% of Pd(II) ion recovered/removed. The physico-chemical characterization of gel beads was also made. SEM micrographs, EDX and FT-IR spectra as well as the values of the physical parameters calculated for each adsorbent material were analysed in order to find correlations between their chemical and physical properties and their behaviour in terms of palladium adsorption.