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Long-Term Experimental Determination of Solubilities of Micro-Crystalline Nd(III) Hydroxide in High Ionic Strength Solutions: Applications to Nuclear Waste Management

Long-Term Experimental Determination of Solubilities of Micro-Crystalline Nd(III) Hydroxide in... In this study, the experimental results from long-term solubility experiments up to 1146 days on micro-crystalline neodymium hydroxide, Nd(OH)3(micro-cr), in high ionic strength solutions at 298.15 K under well-constrained conditions, are presented. Hydrogen ion concentrations in our experiments are controlled by the dissolution of Nd(OH)3(micro-cr) without artificial adjustment with addition of either an acid or a base, preventing the possibility of phase change that could be induced especially by addition of a base. Such an experimental design also provides the information about the hydrogen ion concentrations buffered by the dissolution of Nd(OH)3, which is currently lacking. The solubility data produced in this work, applicable to geological repositories in high ionic strength environments, are compared with the solubilities of Am(OH)3(s) predicted by using the Waste Isolation Pilot Plant (WIPP) thermodynamic model. The predicted values for Am(OH)3(s) are in good agreement with the experimental values for Nd(OH)3(micro-cr) obtained in this work. Our experimental data indicate that the pHm (negative logarithm of hydrogen ion concentration on a molal scale) buffered by dissolution of Nd(OH)3(micro-cr) ranges from ~ 9.5 to ~ 9.9. As the equilibrium constant for amorphous neodymium hydroxide, Nd(OH)3(am), is useful for several fields, the equilibrium constant regarding the dissolution of Nd(OH)3(am) for the following reaction, $$ {\text{Nd}}\left( {\text{OH}} \right)_{3} \left( {\text{am}} \right) + 3{\text{H}}^{ + } = {\text{Nd}}^{3 + } + 3{\text{H}}_{2} {\text{O}}\left( {\text{l}} \right) $$ Nd OH 3 am + 3 H + = Nd 3 + + 3 H 2 O l is also obtained by evaluating the experimental data in a wide range of ionic strengths from the literature by using the WIPP thermodynamic model. The $$ \log_{10} K_{{{\text{s}}0}}^{0} $$ log 10 K s 0 0 at 298.15 K for the above reaction obtained in this work is 16.85 ± 0.20 (2σ), which is similar to, but slightly lower than, the values in the literature evaluated in the low ionic strength range. This value can be applied to amorphous americium hydroxide, Am(OH)3(am), using Nd(III) as an analog to Am(III). http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Aquatic Geochemistry Springer Journals

Long-Term Experimental Determination of Solubilities of Micro-Crystalline Nd(III) Hydroxide in High Ionic Strength Solutions: Applications to Nuclear Waste Management

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References (47)

Publisher
Springer Journals
Copyright
Copyright © 2017 by Springer Science+Business Media B.V., part of Springer Nature
Subject
Earth Sciences; Geochemistry; Hydrology/Water Resources; Hydrogeology; Water Quality/Water Pollution
ISSN
1380-6165
eISSN
1573-1421
DOI
10.1007/s10498-017-9326-6
Publisher site
See Article on Publisher Site

Abstract

In this study, the experimental results from long-term solubility experiments up to 1146 days on micro-crystalline neodymium hydroxide, Nd(OH)3(micro-cr), in high ionic strength solutions at 298.15 K under well-constrained conditions, are presented. Hydrogen ion concentrations in our experiments are controlled by the dissolution of Nd(OH)3(micro-cr) without artificial adjustment with addition of either an acid or a base, preventing the possibility of phase change that could be induced especially by addition of a base. Such an experimental design also provides the information about the hydrogen ion concentrations buffered by the dissolution of Nd(OH)3, which is currently lacking. The solubility data produced in this work, applicable to geological repositories in high ionic strength environments, are compared with the solubilities of Am(OH)3(s) predicted by using the Waste Isolation Pilot Plant (WIPP) thermodynamic model. The predicted values for Am(OH)3(s) are in good agreement with the experimental values for Nd(OH)3(micro-cr) obtained in this work. Our experimental data indicate that the pHm (negative logarithm of hydrogen ion concentration on a molal scale) buffered by dissolution of Nd(OH)3(micro-cr) ranges from ~ 9.5 to ~ 9.9. As the equilibrium constant for amorphous neodymium hydroxide, Nd(OH)3(am), is useful for several fields, the equilibrium constant regarding the dissolution of Nd(OH)3(am) for the following reaction, $$ {\text{Nd}}\left( {\text{OH}} \right)_{3} \left( {\text{am}} \right) + 3{\text{H}}^{ + } = {\text{Nd}}^{3 + } + 3{\text{H}}_{2} {\text{O}}\left( {\text{l}} \right) $$ Nd OH 3 am + 3 H + = Nd 3 + + 3 H 2 O l is also obtained by evaluating the experimental data in a wide range of ionic strengths from the literature by using the WIPP thermodynamic model. The $$ \log_{10} K_{{{\text{s}}0}}^{0} $$ log 10 K s 0 0 at 298.15 K for the above reaction obtained in this work is 16.85 ± 0.20 (2σ), which is similar to, but slightly lower than, the values in the literature evaluated in the low ionic strength range. This value can be applied to amorphous americium hydroxide, Am(OH)3(am), using Nd(III) as an analog to Am(III).

Journal

Aquatic GeochemistrySpringer Journals

Published: Dec 1, 2017

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