Constantes de formation des complexes hydroxydés de l'aluminium en solution aqueuse de 20 a 70°C

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Les constantes de formation des complexes A1(OH) 2+ et Al(OH) 4 - ont été déterminées, par des réactions ne faisant intervenir que des ions en solution, dans la gamme de température 20-70°C. Le couple Al 3+ / A 1( OH ) 2+ a été étudié en mesurant le pH de solutions de concentrations variées de sels d'aluminium. Le couple Al 3+ / A 1( OH ) 4 - a été étudié en comparant les constantes de formation du complexe trioxalato-aluminium Al(C 2 O 4 ) 3 3- à partir de Al 3+ en milieu acide et de Al(OH) 4 - en milieu basique. La constante d'acidité * K 1 du couple Al 3+ / A 1( OH ) 2+ est égale à 10 -5.00 et H = 11.8 Kcal. La constante globale * 4 de Al 3+ / A 1( OH ) 4 - vaut 10 -22.2 et H = 42.45 kcal. Ces dernières valeurs ne sont pas en accord avec les valeurs actuellement admises pour G 0 f et H 0 f de Al 3+ et Al(OH) 4 - En conclusion, nous proposons une série cohérente de données thermodynamiques pour les espèces dissoutes et solides de l'aluminium et pour certains alumine-silicates. Abstract Stability constants of hydroxocomplexes of Al(III):Al(OH) 2+ and A1(OH) 4 - have been measured in the 20-70°C temperature range by reactions involving only dissolved species. The stability constant * K 1 of the first complex ion is studied by measuring pH of solutions of aluminium salts at several concentrations. * 4 of aluminate ion is deduced from equilibrium constants of the reaction between the trioxalato aluminium (III) complex ion and Al 3+ in acid medium, and between the same complex ion and A1(OH) 4 - in alkaline medium. The K values and the associated H are * K 1 = 10 -5.00 and H 1 = 11.8 Kcal; * 4 = 10 -22.20 and H 4 = 42.45 Kcal. These last results are not in agreement with the values of recent tables for G 0 f and H 0 f of Al 3+ and Al(OH) 4 - . We suggest a consistent set of data for dissolved and solid Al species and for some aluminosilicates.

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