AB STRA CT:The kinetic and thermodynamic of the bath sorption of lead (Pb) on to activated carbon from Coconut (CA) and Seed hull of the Palm tree (GA) have been investigated. The effects of initial Pb concentration, contact time and temperature were examined. The results showed that the adsorption capacities of the activated carbons increased with the initial lead concentration. The process sorption followed a pseudo first order kinetics and parameters such as Ea and k 0 were determined. It could be best fitted by the Langmuir and Freundlich isotherms. From the first, the equilibrium sorption capacities of lead ion were determined and found to be respectively 4.38 and 3.77 mg/ g for CA and GA at 60 °C. The thermodynamic parameters such as ∆H, ∆S and ∆G were computed from the experimental data. These values show that the adsorption is endothermic and non spontaneous. Moreover, the relative weak values of ∆H (~5 kcal/mol) confirm a physical adsorption. The maximum adsorptions were obtained at 60 °C, pH 4 and with a Pb initial concentration of 100 mg/L.

First studies of the ternary system SnSe-Bi(2)Se(3) developed in 1960s and 1970s have revealed the existence of a nonstoichiometric trigonal phase with a wide range of compositions. In this study, an almost stoichiometric phase, corresponding to the composition SnBi(4)Se(7), has been identified and isolated. The structure has been determined by X-ray diffraction and the local environment of Sn atoms analyzed by Mössbauer spectroscopy. This phase has a rhombohedral structure, space group R&thremacr;m, with hexagonal lattice parameters a = 4.1602(5) Å and c = 38.934(3) Å. The unit cell contains three slabs, each one composed of seven atomic layers according to the sequence Se-Bi-Se-(Bi,Sn)-Se-Bi-Se. Bismuth atoms partially occupy two sites, 3a (0, 0, 0) and 6c (0, 0, z) with z = 0.4285, while tin atoms partially occupy only one site, 3a. Selenium atoms are placed in two different 6c sites, with z(1) = 0.1350 and z(2) = 0.7108.

We have studied the evolution of the orthorhombic structure of SnSe (space group

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