Acidity constants and redox potentials of uranyl ions in hydrothermal solutions. Issue 37 (9th September 2016)

• Record Type: Journal Article
• Authors: Liu, Xiandong; Cheng, Jun; He, Mengjia; Lu, Xiancai; Wang, Rucheng
• Is Part Of: Physical chemistry chemical physics. Volume 18:Issue 37(2016)
• Page Start: 26040
• Page End: 26048
• Publication Date: 2016-09-09
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c6cp03469a
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : We report a first principles molecular dynamics (FPMD) study of the structures, acidity constants (p K a ) and redox potentials ( E 0 ) of uranyl (UO2 2+ ) from ambient conditions to 573 K. Abstract : We report a first principles molecular dynamics (FPMD) study of the structures, acidity constants (p K a ) and redox potentials ( E 0 ) of uranyl (UO2 2+ ) from ambient conditions to 573 K. It is found that UO2 2+ keeps five coordination up to 573 K whereas UO2 + transforms from 5 to 4-coordinate as temperature increases to 573 K. The FPMD-based vertical energy gap method is used to derive p K a s and E 0 s. The method is validated by comparing with available experimental data (for E 0 under the ambient conditions and for p K a s from ambient conditions to 367 K), with an uncertainty of 1–2 p K a units and 0.2 V for p K a and E 0 . The encouraging results demonstrate that the method may be used to predict the pH–Eh diagrams of f-block elements under the conditions of hydrothermal solutions. The results show that the acidity constants of uranyl decrease with temperature and are lower than 3.0 when the temperature is above 473 K, indicating that hydrolytic forms are dominant for U(vi ) in the near neutral pH range. The reduction potential increases with temperature, indicating that the reduced state is more significant at higher temperatures.