Adsorption of chromium ions in activated carbon

The uptake capacity of chromium ions in an activated carbon bed at 20, 30 and 40 °C was investigated in this work. The experiments were carried out in the pH range 4.0–4.5, with a flow rate of 2 mL/min. Breakthrough curves for feed concentrations from 0.17 up to 3.42 mequiv./L were obtained. The Freundlich model was fitted to the dynamic isotherm experimental data, which was well described by a mathematical model that considered a mass balance in the fluid phase and in the adsorbent assuming the intraparticle diffusion as the rate-controlling step. Thermodynamic parameters such as Gibbs energy free (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) for Cr(III) adsorption were estimated. Results suggest that the adsorption process is a non-spontaneous and endothermic process with positive entropy.