Binary adsorption of silver and copper on Verde-lodo bentonite: Kinetic and equilibrium study

Removal and recovery of toxic metals from wastewater by adsorption is an efficient alternative, especially when using uncommon adsorbents. In the present work, silver and copper binary adsorption onto Verde-lodo bentonite was evaluated in static systems. Kinetic studies under different initial metal concentrations and molar fractions were performed. Kinetic models were adjusted to experimental data, and the External mass transfer resistance model (EMTR) presented the best fitting. The binary kinetic assays revealed that copper presents higher adsorption capacity than silver. Higher total concentrations presented an influence on the adsorption process due to increasing competition for active sites. Equilibrium studies were carried out and the results confirmed the preferential copper adsorption in binary solution with silver. Copper ions were better adsorbed at higher temperatures and silver ions at lower temperatures. The maximum adsorption capacities were 0.110 mmol/g for copper at 60 °C and 0.090 mmol/g for silver at 20 °C. Binary equilibrium models were fitted and the Langmuir-Freundlich model best represented the experimental data. The comparison between Verde-lodo clay characterization, prior and post adsorption, indicated that the process caused no significant changes in the morphology, crystal structure, functional groups and thermal stability of the material.