Molecular dynamics simulations of Y(iii) coordination and hydration properties

Abstract

Y mainly exists in ionic rare-earth resources. During rare-earth carbonate precipitation, rare-earth ion loss in the precipitated rare-earth mother liquor often occurs due to CO32- coordination and Y(iii) hydration. Microscopic information on the coordination and hydration of CO32- and H2O to Y(iii) has not yet been elucidated. Therefore, in this study, the macroscopic dissolution of Y(iii) in different aqueous solutions of Na2CO3 was studied. The radial distribution function and coordination number of Y(iii) by CO32- and H2O were systematically analyzed using molecular dynamics (MD) simulations to obtain the complex ion form of Y(iii) in carbonate solutions. Density functional theory (DFT) was used to geometrically optimize and calculate the UV spectrum of Y(iii) complex ions. This spectrum was then analyzed and compared with experimentally determined ultraviolet-visible spectra to verify the reliability of the MD simulation results. Results showed that Y(iii) in aqueous solution exists in the form of [Y·3H2O]3+ and that CO32- is present in the bidentate coordination form. In 0-0.8 mol L-1 CO32- solutions, Y(iii) was mainly present as the 5-coordinated complex [YCO3·3H2O]+. When the concentration of CO32- was increased to 1.2 mol L-1, [YCO3·3H2O]+ was converted into a 6-coordinated complex [Y(CO3)2·2H2O]-. Further increases in CO32- concentration promoted Y(iii) dissolution in solution in the form of complex ions. These findings can be used to explain the problem of incomplete precipitation of rare earths in carbonate solutions.