Elimination of Chromium (VI) and Cadmium(II) from Aqueous Solutions by Adsorption onto Olive Stones

Abstract

The present study concerns the test of olive stones as an adsorbent for removing Cd(II) and Cr(VI) from aqueous solutions. The experimental elimination of the two cations was carried out batchwise and the influence of certain physico-chemical parameters such as the contact time, the pH of the solution, the temperature, the solid to liquid ratio, the agitation speed were also considered. The equilibrium adsorption capacity of the olive stones for the case of Cr(VI) followed the Langmuir model, whereas for the Cd(II) cations, the two models i.e. Langmuir and Freundlich were equally representative. The adsorption process was found to be of pseudo second order and the rate constants were determined for both cations. The Gibbs free energy sign was negative for the adsorption of both cations, indicating that the process was spontaneous. Finally the olive stones retained chromium more than cadmium, but at optimal conditions, high removal percentages were reached, for both cations.