Kinetic and thermodynamic parameters of iron adsorption onto olive stones

Olive stones biomass, by-product of olive oil industry, has been addressed in the present study as adsorbent for iron. Experimental results have shown that the pretreatments performed have not favored the iron adsorption capacity, demonstrating that direct reuse (as manufactured) or a simple washing with cold and hot water is sufficient. Results obtained indicate that the adsorption process is fast and spontaneous within the first 10-20 min. The experimental data supports both pseudo-first and pseudo-second order models. Kinetic parameters and equilibrium adsorption capacity were found to be increased upon stirring rates above 75 rpm. Also temperature effect was studied. Adsorption capacity values, q(e), raise as temperature increases from 278 to 343 K, pin-pointing for an endothermic adsorption process. The adsorption isotherms were obtained from 5 different temperatures in the ranges of 278-343 K and 5-100 mg dm(-3) iron (III) concentrations. These adsorption data were fitted with Langmuir isotherm. In addition, the mean values of thermodynamic parameters of activation energy (E-a = 8.04kJ mol(-1)), standard free energy (Delta G(0) = -19.51 kJ mol(-1)), standard enthalpy (Delta H-0 = 8.86 kJ mol(-1)) and standard entropy (Delta S-0 = 91.4 J mol(-1) K-1) of the adsorption mechanism were determined. What is more, the present process is environmentally friendly and may be able to reduce the iron load from different effluents, also providing an affordable technology for small and medium-scale industry. (C) 2013 Elsevier B.V. All rights reserved.