Application des modèles de Langmuir et Freundlich aux isothermes d'adsorption des métaux lourds par l'argile purifiée

Bentonite, which consist essentially of clay minerals belonging to the smectite group, have a wide range of chemical and industrial uses. The structure chemical composition, exchangeable-ion type and small crystal size of smectite are responsible for several properties, including a large chemically active surface area, a high cation-exchange capacity and interlamellar surface having usual hydratation characteristics. A sample collected from Zaghouan (North East Tunisia, North Africa) is studied through some physico-chemical methods. Results from X-ray diffraction, chemical analysis, infrared spectroscopy, thermogravimetric analysis (TGA) and differential thermal analysis (DTA), cation exchange capacities, specific and total surfaces, confirm the general smectite character of the sample. The adsorption capacity of this clay was tested out using three metallic ions (Pb$^{2+}$, Zn$^{2+}$, Ni$^{2+}$). The results showed that, in all cases, adsorption can be illustrated by Freundlich or Langmuir isotherms. However, for 10$^{-3}$M Pb$^{2+}$ the low value of the correlation coefficient (R$^{2}$) indicated that the experimental data for the adsorption didn't fit to any linear form of the Langmuir equation. Metal adsorbed onto Zaghouan clay varied in the decreasing order PbPb$^{2+}$ > Zn$^{2+}$ > Ni$^{2+}$ and fitted in satisfactorily with the uptake capacity. For Pb$^{2+}$ the amount of adsorbed ions remained higher than the CEC (cation exchange capacity) of the clay fraction. This result may be due to adsorption of hydroxy lead complex in addition to sorption of bivalent lead form which explains the high amount of Pb$^{2+}$ removed from aqueous solution

Petrological and physico-chemical investigations on an Tunisian glauconitic deposit

The glauconite bearing rocks occurring in lower Eocene deposit of North-East of Tunisia were examined to study the composition and association of glauconite with different minerals. The study was carried out by petrographic investigation, X-ray powder diffraction, Scanning Microscopy with an Energy Depressive System methods.
Green grains are a conspicuous component of the studied material. Although resembling glauconitic minerals in thin-section, electron microprobe analyses and acid treatment indicate that the green grains are formed by glauconite core and phosphate rim.
The nature of (001), (002) and (003) spacing as found in the XRD patterns obtained for purified sample suggest the presence of glauconite mica mineral. XRD identification is amply supported by results of chemical analyses. Those revel high K and Fe contents in purified sample

Oxydation catalytique du Phénol par le peroxyde d'hydrogène en présence d'argiles pontées par des espèces mixtes [Al-Cu]

Various processes can be used for the treatment of wastewater, but the one we feel to be important and more promising is the wet peroxide oxidation (WPO), in the presence of a solid catalyst, at atmospheric pressure and at room temperature. Different types of materials can be used as catalysts for such reactions, but as shown in previous studies dealing with phenol oxidation clays-based catalysts seem to be attractive. It is well known that natural clays are inactive in the phenol oxidation, but the intercalation of polymeric species changes their properties. When the clay is pillared with pure aluminum oxyhydroxides species, the d001 spacing and the surface area increase, but the activity is very low. When the clay is pillared with mixed [Al-Cu] species, there is a strong increase of the phenol conversion. Nevertheless W (Wyoming) based solids are more active than H (Haîdoudi) or L (Laponite) based catalysts. The stability, the activity and the percentage of copper depend on the preparation method