Sectrophotometric Investigation of U(VI) Chloride Complexation in the Naci/NaClO4 system

1999 ◽  
Vol 556 ◽  
Author(s):  
Patricia Paviet-Hartmann ◽  
Mavis R. Lin
Keyword(s):  
Stability Constants ◽  
Chloride Ions ◽  
Solution Chemistry ◽  
Chloride Complexes ◽  
Waste Isolation Pilot Plant ◽  
Vis Spectroscopy ◽  
Weak Complexes ◽  
Naci Concentration ◽  
Radioactive Release ◽  
Apparent Stability

AbstractPost closure radioactive release scenarios from geologic salt formation, such as the WIPP (Waste Isolation Pilot Plant) (USA) include hydrologic transport of radionuclides through a chloride saturated aquifer. Consequently, the understanding of actinide solution chemistry in brines is essential for modeling requiring accurate knowledge of the interaction between AnO22+ and chloride ions. Complexation constants of two U(VI) chloride species UO2Cl+ and UO2Cl20 have been intensively studied for about 40 years using different methods. However, large uncertainties reflect the general difficulty in determining accurate stability constants of weak complexes. In order to model the behavior of U(VI) in brines, we studied the formation of its chloride complexes by UV-Vis spectroscopy as a function of the NaCI concentration at 25 °C. The experiments were performed at constant ionic strength by varying the concentration ratio of NaCI and NaClO4. Deconvolution resulted in single component absorption sepectrum for UO2Cl+ and UO2Cl20. The apparent stability constants of UO2Cl+ and UO2Cl20 are determined at different ionic strengths. The experimental data are used to parameterize using the SIT approach.

Studies on the Coordination Reaction of VO2+ and Tannic Acid in the Tannin Extract Desulfurization

2012 ◽  
Vol 239-240 ◽  
pp. 1573-1576
Author(s):  
Zhu Qing Gao ◽  
Xiao Dong Cai ◽  
Kai Cheng Ling
Keyword(s):  
Stability Constants ◽  
Tannic Acid ◽  
Ph Value ◽  
Protonation Constants ◽  
Conditional Stability ◽  
Tannin Extract ◽  
Acid Effect ◽  
Different Temperatures ◽  
The Stability ◽  
Apparent Stability

At different temperatures, the protonation constants of tannic acid and the complex apparent stability constants between tannic acid and VO2+ were determined by using pH potentimetric method. The results showed that the protonation constants and the complex apparent stability constants slightly decreased with the raising temperature. In accordance with the pH value in the tannin extract technology, the conditional stability constants of the complex were calculated on the basis of the acid effect of tannic acid and the hydrolysis effect of VO2+. It was found that pH greatly affected the stability constants of the complex , so pH must be strictly controlled in the tannin extract technology.

Effect of Simulated Concrete Pore Solution Chemistry, Chloride Ions, and Temperature on Passive Layer Formed on Steel Reinforcement

2014 ◽  
Vol 111 (4) ◽  
Author(s):  
Abdulrahman Alhozaimy ◽  
Raja Rizwan Hussain ◽  
Abdulaziz Al-Negheimish ◽  
Rajeh Al-Zaid ◽  
D. D. N. Singh
Keyword(s):  
Pore Solution ◽  
Passive Layer ◽  
Chloride Ions ◽  
Steel Reinforcement ◽  
Solution Chemistry

A spectrophotometric study of Fe(II)-chloride complexes in aqueous solutions from 10 to 100°C

2001 ◽  
Vol 79 (2) ◽  
pp. 131-144 ◽  
Author(s):  
Renhai Zhao ◽  
Pujing Pan
Keyword(s):  
Stability Constants ◽  
Near Infrared ◽  
Chloride Concentration ◽  
Pitzer Model ◽  
Nonlinear Least Squares ◽  
Ionic Species ◽  
Spectrophotometric Study ◽  
Chloride Complexes ◽  
Near Ir ◽  
Coordination Change

The absorption spectra of Fe(II)-chloride solutions were measured in both the UV (ultraviolet) and near-IR (near infrared) regions at temperatures ranging from 10 to 100°C with chloride concentrations from 0.1 to 16 mol kg-1. The stability constants of all Fe(II)-chloride complexes were derived from the spectra using a non-negative nonlinear least-squares computer program (SQUAD). Earlier work on this system reported in the literature was rigorously reassessed. The activity coefficients of the ionic species were calculated using both the Pitzer model and the Helgeson model. The results obtained with UV and near-IR spectra and with different activity coefficient calculation models are in general agreement. Other useful thermodynamic data, including the Gibbs energies, enthalpies, and entropies for complex formation, were also obtained. It was found that the Fe(II)-chloride complexes gradually undergo a configuration transformation from octahedral to tetrahedral coordination as the temperature and (or) chloride concentration increases. This coordination change is of significant importance to the nuclear reactors, as the presence of the tetrahedral complex can increase the solubility of iron in steam generator crevices.Key words: Fe(II)-chloride complexes, stability constants, solution thermodynamics, spectrophotometry, reactor chemistry.

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