Desorption of cadmium (Cd) from sand was studied by both batch and flow-through methods. Batch experiments were conducted at three pH values (5.5, 6.0 and 6.5). In each case, the amount of Cd desorbed was low compared with the quantity of Cd adsorbed previously. Desorption of Cd in the batch experiments can be described adequately by a Freundlich isotherm. The Freundlich isotherm coefficient, Kf, increased with pH. Hysteresis between the sorption/desorption isotherms was observed in all batch experiments. Flow-through experiments in soil columns were conducted for the same three pH values, with the results used to determine transport and sorption/desorption parameters. Again, the desorption isotherms bore little resemblance to the corresponding adsorption isotherms. The experimental breakthrough curves were well fitted by a nonequilibrium desorption model, however the time scale of the desorption process was much larger than measured in batch experiments. This model was therefore rejected as lacking realism. A simple linear retardation (including hysteresis) model that utilises different isotherms was found to simulate column breakthrough curves well. The Freundlich isotherm coefficients, Kf, in all batch and flow-through desorption experiments were different to values evaluated from the corresponding adsorption experiments. However, in contrast to adsorption, desorption in flow-through experiments was not noticeably affected by changes in pH. The effect of pore-water velocity on desorption was also studied at pH 6.0. No trend was established between flow velocity and the desorption coefficient.

Cadmium desorption in sand

Etude de l’élimination des métaux lourds (Cu, Zn, Pb et Cd) contenus dans les eaux usées de Marrakech par quatre systèmes expérimentaux : Lagunage anaérobie, lagunage aéro- anaérobie, sur-irrigation drainage et infiltration - percolation

This study presents the results of retention of heavy metals in aqueous solution by sorption using a biomaterial derived from shellfish from the coast of Béjaia. Characterization by different analytical methods (XRD, IR, SEM, TGA) of this material revealed that it consists of 100% aragonite (CaCO3). The tests performed in batch, using the fraction of particles with a diameter less than 0.2 mm shell powder shows that the capacity to eliminate ions Cd and Zn is very dependent on the pH of the solution. Indeed, the latter increases in the presence of aragonite and causes the release of Ca in the solution. Therefore the initial pH was set at 4, pH value for which the final solutions are lower than the pH of precipitation of metal ions selected. This study also shows a maximum retention averaged more than 90% of zinc and cadmium ions were selected by different retention mechanisms (adsorption on the surface of the aragonite, precipitation and cation exchange) for different initial concentrations of metal ions. Kinetic models of pseudo first order, second order and intraparticle diffusion model were also studied; the correlation coefficients and rate constants of each model were calculated and discussed. It was shown that the adsorption of ions Cd and Zn by aragonite is described by the kinetic equation of pseudo first order. On the adsorption isotherms of metal ions studied, the application of models of Langmuir, Freundlich, Temkin and the Elovich model shows that the adsorption of Zn and Cd is described by the Freundlich model. REMERCIEMENTS 25 octobre 2010 A ma mère A M. Chérif A mes frères et sœurs À toutes les personnes qui m’ont permis d’en arriver là, à toutes celles qui m’ont écoutée, soutenue et remonté le moral, merci.... REMERCIEMENTS 25 octobre 2010

Adsorption des metaux lourds par la poudre de coquillages de la cote de Bejaia.

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Adsorption des metaux lourds par la poudre de coquillages de la cote de Bejaia.