Electrolyte ion effects on Cd2+ binding at Al2O3 surface: specific synergism versus bulk effects.

Cd(2+) binding on gamma-Al(2)O(3) was studied in the presence of the common electrolyte ions Mg(2+), SO(4)(2-), and NO(3)(-) at high and low concentrations. Direct measurements were performed for Cd(2+) as well as for electrolyte ion adsorption as a function of pH. The experimental data reveal that Cd(2+) binding on gamma-Al(2)O(3) is modulated by the electrolyte ions in a complex manner. At high electrolyte concentration, Cd(2+) uptake by gamma-Al(2)O(3) is inhibited. Theoretical analysis by a surface complexation model shows that this effect can be attributed partially to bulk, ionic strength, and effect of the electrolyte, but the most significant inhibition is due to direct competition between Mg(2+) and Cd(2+) ions for the [triple bond]SO(-) surface sites of gamma-Al(2)O(3). At low concentration of electrolyte ions, Cd(2+) uptake by gamma-Al(2)O(3) can be enhanced due to synergistic co-adsorption of Cd(2+) and electrolyte anions, particularly SO(4)(2-) and to a lesser extent NO(3)(-). The theoretical analysis shows that this co-adsorption is due to formation of ternary surface species ([triple bond]SOH(2)SO(4)Cd) and ([triple bond]SOH(2)NO(3)Cd) which enhance Cd-uptake at pH values well below the point of zero charge of the gamma-Al(2)O(3).

Physicochemical study of amino-functionalized organosilicon cubes intercalated in montmorillonite clay: H-binding and metal uptake.

Two organic-modified montmorillonite clays were prepared by embedding organosilanes bearing different chelating amino-functional groups [Apteos] (3-amino-propyltriethoxysilane), and [Edaptmos] (3-(2-aminoethylamino)propyltrimethoxysilane), in the interlayer space of a Zenith montmorillonite. XRD and FTIR spectroscopic data show that the amino organosilanes are intercalated into the interlamelar space forming cube-like structures bearing one polymanino tail at each cube apex. The intercalated cubes cause an increase of the interlayer spacing of the clay sheets by 6.6 A in [Zenith-Apteos] and by 7.1 A in [Zenith-Edaptmos]. The H-binding properties of the intercalated polyamino organosilanes were studied by potentiometric titration. The Cu-, Cd-, and Pb-binding capacity of [Zenith-Apteos] and [Zenith-Edaptmos] were evaluated in aqueous solution as a function of the pH. Both [Zenith-Apteos] and [Zenith-Edaptmos] showed improvement vs Zenith for metal binding in the order Cu > Pb > Cd. [Zenith-Edaptmos] showed the most important results vs Zenith. Theoretical analysis of the pH edge, achieved by a surface complexation model, shows that (a) the amino-functionalized cube-like structures constitute high affinity metal-binding sites; and (b) the metal ions are bound in a monodendate mode with the amino group of the cube, thus resulting in a maximization of metal-binding efficiency.