Startseite Solubilities and solubility products of thorium hydroxide under moderate temperature conditions
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Solubilities and solubility products of thorium hydroxide under moderate temperature conditions

  • Shogo Nishikawa , Taishi Kobayashi EMAIL logo , Takayuki Sasaki und Ikuji Takagi
Veröffentlicht/Copyright: 30. März 2018

Abstract

The Th solubilities of the sample solutions that initially contained Th(OH)4(am) prepared by undersaturation and oversaturation methods in the pHc range of 2.0–8.0 in a 0.5 M ionic strength solution of NaClO4 and HClO4 and stored at aging temperatures (Ta) of 298, 313 and 333 K were investigated in this study. After a certain period of time up to 40 weeks depending on Ta, supernatants of the sample solutions were ultrafiltrated through 3 kDa membranes under the measurement temperature (Tm) of 298, 313 and 333 K. Size distributions of the colloidal species were investigated by ultrafiltration using membranes with different pore sizes ranging from 3 to 100 kDa, and the solid phases were examined by X-ray diffraction (XRD). The solubility of the sample solutions obtained after aging at Ta=298 K using undersaturation method with continuous shaking was similar to those of dried precipitate of Th hydroxide. The solubilities obtained after aging at Ta=313 and 333 K were lower than those at Ta=298 K. The XRD spectra suggested that the crystallization of the solid phase proceeded under these elevated temperatures. The solubility of the sample solutions obtained after aging at Ta=333 K using the oversaturation technique were similar to those prepared by undersaturation method and aged at the same Ta. A slight temperature dependence of the apparent solubilities on the Tm was observed in the sample solutions prepared by both methods. The solubility products (Ksp,Ta(Tm)) after different Ta and Tm were determined from the solubility analysis. The observed increase in the formation constant (Ks,Ta(Tm)) of Th4++(4+x)H2O(1)⇌Th(OH)4·xH2O(s,Ta)+4H+ with increasing Tm indicated that the reaction was endothermic. The enthalpy change (ΔHrm_Tacr°) between the solid phases of Th(OH)4·xH2O(s,Ta) and ThO2(cr) suggested that the solid phase transformation from Th(OH)4·xH2O(s,Ta) to ThO2(cr) contains an endothermic process.

Acknowledgments

This study was partially conducted under the Visiting Researchers Program of the Kyoto University Research Reactor Institute (KURRI). This work was supported by the JSPS Grant-in-Aid for Young Scientists (B) Grant Number 16K18348.

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Received: 2017-12-15
Accepted: 2018-02-07
Published Online: 2018-03-30
Published in Print: 2018-08-28

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