JOURNAL of the Tunisian Chemical Society

serving the Research, the Education and the Industry

Etude de l'Entartrage par les Eaux Géothermales: Influence du Bois sur la Précipitation de CaCO3

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The atmospheric cooling towers, used for the cooling of geothermal waters of the south of Tunisia, are equipped of laths in wood. Comparing to other walls, wood has a different behaviour vis-a-vis of scaling phenomenon. A comparative study between two types of wood (new and used) and the PVC has been done. This study showed that the new wood has an inhibitory role, on CaCO3 precipitation, by freeing certain acidity in the solution. Contrarily, the used wood, descaled mechanically, becomes a veritable support of crystallization. Wood has affinity to Ca2+ ions in solution at pH superior to 7, permitting so the reduction of the water scaling power. While at acidic pH, wood liberates Ca2+ ions.

A. S. Manzola, H. El Fil, M. Ben Amor

Geothermal waters, Scaling, Wood, Calcium Carbonate

Pages 145-157

Etude thermique et texturale de la kaolinite de Sejnène (Tunisie)

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A fundamental study of the quality of the kaolinite coming from the deposit of Sejnène (Tunisia) has been carried out in the framework of the valorization of the Tunisian clay resources. The study uses Controlled Rate Thermal Analysis (CRTA), isothermal adsorption of nitrogen at 77K and calorimetry of argon adsorption at 77K. The kinetic analysis of kaolinite by CRTA method, under 10-3 mbar, reveals that the dehydroxylation occurs according to a three-dimensional mechanism (D3) with an apparent activation energy equal to 230 (±15) kJ.mol-1. The thermal treatment of the studied kaolin ite until a decomposition rate of 99 %, practically does not change the specific surface area (constantly equal to 36 m2.g-1). The microcalorimetry of argon adsorption allows to distinguish the basal and the lateral faces of the kaolinite.

K. Nahdi, P. Llewellyn, F. Rouquerol, N.K. Ariguib, M.T. Ayedi

kaolinite, argile Sejnène, ATVC, microcalorimétrie, isotherme d'adsorption

Pages 159-170

Characterization of a new organic-cation dihydrogenmonoarsenate: [C4H12N]H2AsO4

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Physicochemical properties of an organic dihydrogenmonoarsenate are discussed on the basis of its X-ray crystal structure investigation. [C4H12N)H2AsO4, denoted tBAs, crystallizes in the monoclinic system with P21/c space group. Its unit cell dimensions are a = 14.2655(7); b = 6.3265(2), c = 17.9401(7) Å, β = 147.261(2)° with V = 875.63(6) Å3 and Z = 4. The structure has been solved using direct method and refined to a reliability R factor of 0.039 for 1447 reflections. The compound is characterized by infinite [H2AsO4]nn- chains, parallel to the b direction, connected by organic cations and fanning layers localized at x = 1/2. The cohesion of the framework is ensured by hydrogen bonds N(O)–H...O. Thermal behavior exhibits an irreversible phase transition. IR bands are attributed by comparison with spectra of similar other compounds.

A. Chtioui, T. Guerfel, L. Benhamada, A. Jouini

Organic dihydrogenmonoarsenate, Chemical preparation, Crystal structure, Thermal behavior, Infrared spectroscopy

Pages 171-179

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