Modelling of the adsorption of the chromium ion by modified clays

This paper presents our contribution to the removal of chromium ions from aqueous solution by adsorption. The adsorbent used is bentonite clay coming from south Tunisian. This clay has been modified by several treatments such as aluminium pillaring, acid activation and pillared followed by acid activation. Acid activation involved a destruction partial of the octahedral layer by dissolution of the cations, Al3+, Mg2+ and Fe3+ of this layer and an amorphous silica formation due to the destruction of the tetrahedral layer. This treatment involved a reduction in the cation capacity of exchange and an increase in the specific surface which reaches respectively 154, 354 m(2)/g after treatment with HCl 0.5 M and HCl 3 M. These adsorbent are used to fix chromium starting from the aqueous solutions at pH = 5. The maximum of adsorption differs according to the treatment. The retention of chromium is correlated with the variation of the values of the cation exchange capacities and not with the values of specific surfaces. The concentrations of metal ions have been measured by batch techniques and with AAS (analysis adsorption). The adsorption analysis has been correlated to Langmuir and Freundlich models.