Uranyl Arsenate Complexes in Aqueous Solution: Insights from First-Principles Molecular Dynamics Simulations.

ABSTRACT

In this study, the structures and acidity constants (p Ka's) of uranyl arsenate complexes in solutions have been revealed by using the first principle molecular dynamics technique. The results show that uranyl and arsenate form stable complexes with the U/As ratios of 11 and 12, and the bidentate complexation between U and As is highly favored. Speciation-pH distributions are derived based on free energy and p Ka calculations, which indicate that for the 11 species, UO2(H2AsO4)(H2O)3+ is the major species at pH < 7, while UO2(HAsO4)(H2O)30 and UO2(AsO4)(H2O)3- dominate in acid-to-alkaline and extreme alkaline pH ranges. For the 12 species, UO2(H2AsO4)2(H2O)0 is dominant under acid-to-neutral pH conditions, while UO2(HAsO4)(H2AsO4)(H2O)-, UO2(HAsO4)(HAsO4)(H2O)2-, and UO2(AsO4)(HAsO4)(H2O)3- become the major forms in the pH range of 7.2-10.7, 10.7-12.1, and >12.1, respectively.