Silver sorption isotherms onto bentonites: Comparing mathematical models

Herein is reported the application of models on sorption isotherms for removal of silver ions from aqueous solution using 2 bentonites: SWy-2 and BaVC-1, low-cost sorbents. Physicochemical attributes were determined for both materials, and sorption experiments were carried out in batch system. The pH before and after sorption decreased from 7.8 to 6.1 and 8.4 to 6.7 for SWy-2 and BaVC-1, respectively. Langmuir, Freundlich, Sips, Toth, Kolbe-Corrigan, Khan, and Radke-Prausnitiz models were applied to the data. The models showed good fit with R-2 above 0.999 and RMSE<2%. The adjustable parameters indicated high affinity of silver ions to BaVC-1 sorption sites, demonstrating high sorption capacity and thermodynamic feasibility. In general, SWy-2 showed most heterogeneous sorption sites, while BaVC-1 showed most homogeneous sites. Moreover, BaVC-1 has shown larger surface area and smaller particle size, which can explain its better sorption performance as compared with SWy-2.