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Issues concerning the determination of solubility products of sparingly soluble crystalline solids: solubility of HfO2(cr)

Journal Article · · Radiochimica Acta
 [1];  [2];  [3];  [4];  [4]
  1. VISITORS
  2. Japan Atomic Energy Agency
  3. BATTELLE (PACIFIC NW LAB)
  4. Kyoto University
+ Show Author Affiliations
Solubility studies were conducted with HfO2(cr) solid as a function HCl and ionic strength ranging from 2.0 to 0.004 mol kg -1. These studies involved 1) using two different amounts of the solid phase, 2) acid washing the bulk solid phase, 3) preheating the solid phase to 1400 °C, and 4) heating amorphous HfO2(am) suspensions to 90°C to ascertain whether the HfO2(am) converts to HfO2(cr) and to determine the solubility from the oversaturation direction. Based on the results of these treatments it is concluded that the HfO2(cr) contains a small fraction of less crystalline, but not amorphous, material [HfO2(lcr)] and this, rather than the HfO2(cr), is the solubility-controlling phase in the range of experimental variables investigated in this study. The solubility data are interpreted using both the Pitzer and SIT models and they provide log10 ??0 values of -(59.75±0.35) and -(59.48±0.41), respectively, for the solubility product of HfO2(lcr) [HfO2(lcr) + 2H2O Hf4+ + 4OH - ]. The log 10 of the solubility product of HfO2(cr) is estimated to be < -63. The observation of a small fraction of less crystalline higher solubility material is consistent with the general picture that mineral surfaces are often structurally and/or compositionally imperfect leading to a higher solubility than the bulk crystalline solid. This study stresses the urgent need, during interpretation of solubility data, of taking precautions to make certain that the observed solubility behavior for sparingly-soluble solids is assigned to the proper solid phase.
Research Organization:
Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
Sponsoring Organization:
USDOE
DOE Contract Number:
AC05-76RL01830
OSTI ID:
1737362
Report Number(s):
PNNL-SA-118165
Journal Information:
Radiochimica Acta, Journal Name: Radiochimica Acta Journal Issue: 8 Vol. 104
Country of Publication:
United States
Language:
English

References (11)

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Comparisons between intrinsic bonding defects in d0 transition metal oxide such as HfO2, and impurity atom defects in d0 complex oxides such as GdScO3 journal December 2009
The Aqueous Solubility of Hafnium Oxide by the Radioactive Isotope Technique journal August 1951
The role of dislocations and surface morphology in calcite dissolution journal March 1992
Weathering of the primary rock-forming minerals: processes, products and rates journal September 2004
An electron microscope study of hydrous thorium dioxide ThO2 · nH2O journal January 1985
The kinetics and mechanism of MgO dissolution journal December 1999
Direct Observations of the Dissolution of Fluorite Surfaces with Different Orientations journal December 2013
The prediction of mineral solubilities in natural waters: The Na-K-Mg-Ca-H-Cl-SO4-OH-HCO3-CO3-CO2-H2O system to high ionic strengths at 25°C journal April 1984
Fundamental Controls of Dissolution Rate Spectra: Comparisons of Model and Experimental Results journal January 2013

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