Surface-charge properties and UO{sub 2}{sup 2+} adsorption of a subsurface smectite

Journal Article · Sun Sep 01 04:00:00 EDT 1996 · Geochimica et Cosmochimica Acta

DOI:https://doi.org/10.1016/0016-7037(96)00169-X· OSTI ID:543180

Turner, G D; Zachara, J M; McKinley, J P; Smith, S C ^[1]

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1. Pacific Northwest National Lab., Richland, WA (United States)

Surface charge and UO{sub 2}{sup 2+} adsorption were measured on a clay-sized, subsurface mineral isolate whose mineralogy was dominated by a ferrogenous beidellite. Experiments were performed in batch at 25{degrees}C with N{sub 2(g)} atmosphere and sorbent suspensions (9.46 g clay/kg suspension) that had been adjusted in pH between 4 and 9. Surface charge was defined by measurements of adsorbed Na by isotopic exchange and of proton adsorption by potentiometric titration in NaClO{sub 4} (I = 0.1, 0.01, 0.001). Extraction of the clay with La(NO{sub 3}){sub 3} and aqueous-phase analyses were necessary to establish the contributions of Al and Si dissolution to the proton balance and the total absorbed cation charge (i.e., Na{sub ads}{sup +} + 3Al{sub ads}{sup 3+}). The adsorption of UO{sub 2}{sup 2+} (7.5 {times} 10{sup {minus}6} mol L{sup {minus}1}) was determined in Na{sup +} (0.1, 0.01, 0.001 mol L{sup {minus}1}) and Ca{sup 2+} (0.05 and 0.005 mol L{sup {minus}1}) electrolytes. Adsorption of UO{sub 2}{sup 2+} showed contributions of ion exchange and edge complexation reactions in Na{sup +} electrolyte, but by only edge complexation reactions in Ca{sup 2+} electrolyte. A multiple-site surface-complexation model containing fixed-(X{sup {minus}}) and variable-charge sites (SiOH, AlOH) was fit to adsorbed cation charge data between pH 4 and 10, with the concentrations of AlOH, SiOH, and X{sup {minus}} as the adjustable parameters. Surface acidity and ion-pair formation constants for gibbsite and silica were used to described the ionization and electrolyte binding of the AlOH and SiOH sites. The model provided an excellent description of the surface-charge characteristics of the clay as measured by sodium isotopic exchange and potentiometric titration. 62 refs., 7 figs., 5 tabs.

• DOE Contract Number: AC06-76RL01830
• OSTI ID: 543180
• Journal Information: Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: 18 Vol. 60; ISSN 0016-7037; ISSN GCACAK
• Country of Publication: United States
• Language: English

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