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Solubility of Niobium(V) under Cementitious Conditions: Importance of Ca-niobate

Published online by Cambridge University Press:  17 March 2011

Caterina Talerico
Affiliation:
BMG Engineering Ltd., Ifangstrasse 11, CH-8952 Schlieren-Zürich, Switzerland
Michael Ochs
Affiliation:
BMG Engineering Ltd., Ifangstrasse 11, CH-8952 Schlieren-Zürich, Switzerland, michael.ochs@bmgeng.ch
Eric Giffaut
Affiliation:
ANDRA, Parc de la Croix Blanche, 1/7 rue Jean Monnet, F-92298 Châtenay-Malabry, France
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Abstract

The solubility of niobium was investigated for Ca and pH conditions relevant for cementequilibrated solutions. For the pH range considered (9.5-13.2), the dissolved Nb concentration decreases with increasing pH. Overall, experiments lead to Nb concentrations between 2·10-5 M and 2·10-9 M. For all pH values, the dissolved Nb concentration also decreases systematically with increasing Ca concentration. X-ray diffraction measurements of selected experiments confirmed the presence of a solid Ca-Nb-oxide phase, with CaNb4O11·8H2O (hochelagaite) being the most likely composition. On the basis of these findings an empirical regression model for the prediction of Nb solubility data as a function of pH and Ca concentration was derived. This empirical relation is consistent with the presence of a solubility limiting Ca-Nb solid phase and permits to predict aqueous Nb solubility values in cementitious environments over a relatively wide range of conditions. Predicted values are in good agreement with independent experimental results.

Type
Research Article
Copyright
Copyright © Materials Research Society 2004

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