Molecular Dynamics Calculation of the Coordination Behavior of Yb (III) in Sodium Carbonate Solution

Abstract

Yb (III) shows complex behavior of coordination dissolution and precipitation in carbonate solutions, but the properties of CO32− coordination and hydration to Yb (III) in the solution have not been explicated. In this work, the dissolution rule of Yb (III) with CO32− concentration has been studied. The radial distribution function and the coordination number of CO32− and H2O to Yb (III) were calculated by molecular dynamics simulation, and the complex ion form of Yb was obtained. The ultraviolet–visible spectrum and the ionic structures of Yb (III) complex ions were geometrically optimized and calculated by using density functional theory. Then, the experimental ultraviolet–visible spectra and density functional theory results were combined to verify the molecular dynamics calculations. The results indicate that Yb (III) undergoes precipitation in low-concentration carbonate solution, but, in high-concentration carbonate solution, Yb (III)’s carbonates will undergo dissolution. The main reason for the dissolution of Yb (III)’s carbonates is the coordination effect of CO32− on Yb (III); the coordination of carbonate on Yb (III) occurs with a CO32− concentration range of 0.4~2.0 mol·L−1. Yb (III) mainly exhibits [Yb·9H2O]3+ hydrated form in the aqueous solution, while, in the carbonate solution, [Yb·9H2O]3+ is converted into [Yb(CO3)2·5H2O]− complex. [Yb(CO3)2·5H2O]− complex is the main ionic form in high-concentration carbonate solutions. The analysis method in this work provides guidance for understanding the coordination and hydration characteristics of oxyacid radicals to rare earth elements.