Zeolites were synthesized from natural Tunisian clay by hydrothermal treatment under high pressure (100 MPa H 2 O pressure) at different gradients of temperature in high pressure autoclaves. The natural clay was first heated at 650 °C (HC-heated clay) and then transformed to an amorphous phase at 650 °C by adding different amount of NaOH. By increasing temperature and NaOH content, low-density frameworks zeolites like faujasite are transformed into more stable zeolites having higher density frameworks like cancrinite due to dissolution and recrystallisation steps. Cancrinite (Na 8 (H 2 0) 2 CO 3 [Al 6 Si 6 O 24 ]) (IZA-code: CAN) was successfully synthesized with a good purity. The synthesized CAN was characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The removal performance of heavy metal ions (Cd 2+ , Pb 2+ ) from solution by pure CAN and clays has been studied. The kinetics of adsorption of Cd 2+ and Pb 2+ are very fast: equilibrium is reached within 2 minutes at 298K. The capacity of adsorption of CAN is higher for Pb 2+ (192 mg/g) than for Cd 2+ (68 mg/g). Adsorption equilibrium of Cd 2+ and Pb 2+ on CAN were well represented by Langmuir equation although the thermodynamic study reveals a more complex mechanism: thermodynamic parameters, such as equilibrium constant, free energy, entropy and enthalpy for adsorption were obtained from the experimental data, including adsorption microcalorimetry.

Paracresol is a protein-bound toxin that is not efficiently eliminated by the hemodialysis method. Monte Carlo simulations in grand-canonical (GCMC) and canonical ensembles were performed to investigate the adsorption of paracresol and water in silicalite-1 zeolite. GCMC simulations using a configurational-biased algorithm show that four paracresol molecules are adsorbed at the channel intersections per unit cell of silicalite-1. The adsorption isotherms of water with and without the presence of paracresol at the intersections were investigated. A cooperative phenomenon in the process of coadsorption has been observed: at very low chemical potential, paracresol facilitates the penetration of water into silicalite-1. This mechanism is interpreted in terms of the properties of the zeolite and paracresol molecules. A thermodynamic cycle is used to calculate the adsorption energy of paracresol in silicalite-1. The calculated adsorption energy reasonably agrees with the experimental data.

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Synthesis of Nanocrystalline Low Temperature Silica Polymorphs. -The low-temp. α-quartz modification is obtained from the hydrothemal treatment of colloidal SiO2 over a wide condition range (125-220°C, 100 MPa water pressure, 5-90 d). The samples are characterized by powder XRD, SEM, and TEM. The α-quartz prepared at ≤145°C is nanocrystalline and may be interesting for its adsorption-desorption properties combined with inertness with respect to pharmaceutical and biochemical substances. -(SCHAEF*, O.; GHOBARKAR, H.; GARNIER, A.; VAGNER, C.; LINDNER, J. K. N.; HANSS, J.; RELLER, A.; Solid State Sci. 8 (2006) 6, 625-633; MADIREL, CNRS, Univ. Provence, F-13331 Marseille, Fr.; Eng.) -W. Pewestorf 36-199