# A Thermodynamic Model for ZrO2(am) Solubility at 25°C in the Ca2+–Na+–H+–Cl−–OH−–H2O System: A Critical Review

A Thermodynamic Model for ZrO2(am) Solubility at 25°C in the... Zirconium is an important element in the nuclear fuel cycle. Thermodynamic data and models to reliably predict Zr–OH system behavior in various conditions including high ionic strengths are required and currently are unavailable. Most available experimental data are rather old, obtained using inadequate methodologies, and provide equilibrium constant values that differ by many orders of magnitude. Previous reviews have recommended values based on available data. These reviews used all of the available data, including poor quality data, in a global fit to determine these values. This has resulted in recommended thermodynamic models with a large number of polynuclear species and a number of mononuclear species with values of thermodynamic constants for the solubility product of ZrO2(am) and Zr–OH hydrolysis constants that are many orders of magnitude different from those for the reliable analogous Hf reactions. In this critical review, we have evaluated the quality of the available data, selected only those data that are of high quality, and reinterpreted all of the high quality data using SIT and Pitzer models for applications to high ionic strength solutions. Herein for 25 °C we (1) present formation constant values for ZrOH3+, $${\text{Zr}}\left( {\text{OH}} \right)_{2}^{2 + }$$ Zr OH 2 2 + , Zr(OH)4(aq), $${\text{Zr}}\left( {\text{OH}} \right)_{5}^{ - }$$ Zr OH 5 - , and $${\text{Zr}}\left( {\text{OH}} \right)_{6}^{2 - }$$ Zr OH 6 2 - , and the solubility product for ZrO2(am) which are consistent with the Hf system, (2) report a revised value for the formation constant of $${\text{Ca}}_{3} {\text{Zr}}\left( {\text{OH}} \right)_{6}^{4 + }$$ Ca 3 Zr OH 6 4 + , (3) show that several hypothetical polynuclear species ( $${\text{Zr}}_{3} \left( {\text{OH}} \right)_{9}^{3 + }$$ Zr 3 OH 9 3 + , Zr4(OH) 15 + , and Zr4(OH)16(aq)) proposed in previous reviews are not needed, and (4) show that polynuclear species ( $${\text{Zr}}_{3} \left( {\text{OH}} \right)_{4}^{8 + }$$ Zr 3 OH 4 8 + and $${\text{Zr}}_{4} \left( {\text{OH}} \right)_{8}^{8 + }$$ Zr 4 OH 8 8 + ) are not important in a very extensive H+ concentration range (0.1–10−15.4 mol·kg−1). Our review has also resulted in SIT and Pitzer ion-interaction parameters applicable to as high ionic strength solutions as 5.6 mol·kg−1 in NaCl, 2.11 mol·kg−1 in CaCl2, and 23.5 mol·kg−1 in NaOH. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Solution Chemistry Springer Journals

# A Thermodynamic Model for ZrO2(am) Solubility at 25°C in the Ca2+–Na+–H+–Cl−–OH−–H2O System: A Critical Review

, Volume 47 (5) – May 25, 2018
37 pages

/lp/springer_journal/a-thermodynamic-model-for-zro2-am-solubility-at-25-c-in-the-ca2-na-h-dIWBbGUw7f
Publisher
Springer Journals
Subject
Chemistry; Physical Chemistry; Industrial Chemistry/Chemical Engineering; Geochemistry; Oceanography; Inorganic Chemistry; Condensed Matter Physics
ISSN
0095-9782
eISSN
1572-8927
D.O.I.
10.1007/s10953-018-0766-4
Publisher site
See Article on Publisher Site

### Abstract

Zirconium is an important element in the nuclear fuel cycle. Thermodynamic data and models to reliably predict Zr–OH system behavior in various conditions including high ionic strengths are required and currently are unavailable. Most available experimental data are rather old, obtained using inadequate methodologies, and provide equilibrium constant values that differ by many orders of magnitude. Previous reviews have recommended values based on available data. These reviews used all of the available data, including poor quality data, in a global fit to determine these values. This has resulted in recommended thermodynamic models with a large number of polynuclear species and a number of mononuclear species with values of thermodynamic constants for the solubility product of ZrO2(am) and Zr–OH hydrolysis constants that are many orders of magnitude different from those for the reliable analogous Hf reactions. In this critical review, we have evaluated the quality of the available data, selected only those data that are of high quality, and reinterpreted all of the high quality data using SIT and Pitzer models for applications to high ionic strength solutions. Herein for 25 °C we (1) present formation constant values for ZrOH3+, $${\text{Zr}}\left( {\text{OH}} \right)_{2}^{2 + }$$ Zr OH 2 2 + , Zr(OH)4(aq), $${\text{Zr}}\left( {\text{OH}} \right)_{5}^{ - }$$ Zr OH 5 - , and $${\text{Zr}}\left( {\text{OH}} \right)_{6}^{2 - }$$ Zr OH 6 2 - , and the solubility product for ZrO2(am) which are consistent with the Hf system, (2) report a revised value for the formation constant of $${\text{Ca}}_{3} {\text{Zr}}\left( {\text{OH}} \right)_{6}^{4 + }$$ Ca 3 Zr OH 6 4 + , (3) show that several hypothetical polynuclear species ( $${\text{Zr}}_{3} \left( {\text{OH}} \right)_{9}^{3 + }$$ Zr 3 OH 9 3 + , Zr4(OH) 15 + , and Zr4(OH)16(aq)) proposed in previous reviews are not needed, and (4) show that polynuclear species ( $${\text{Zr}}_{3} \left( {\text{OH}} \right)_{4}^{8 + }$$ Zr 3 OH 4 8 + and $${\text{Zr}}_{4} \left( {\text{OH}} \right)_{8}^{8 + }$$ Zr 4 OH 8 8 + ) are not important in a very extensive H+ concentration range (0.1–10−15.4 mol·kg−1). Our review has also resulted in SIT and Pitzer ion-interaction parameters applicable to as high ionic strength solutions as 5.6 mol·kg−1 in NaCl, 2.11 mol·kg−1 in CaCl2, and 23.5 mol·kg−1 in NaOH.

### Journal

Journal of Solution ChemistrySpringer Journals

Published: May 25, 2018

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