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 CO₃ ²⁻ coordination and Y(III) hydration. Microscopic information on the coordination and hydration of CO₃ ²⁻ 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 CO₃ ²⁻ 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 CO₃ ²⁻ is present in the bidentate coordination form. In 0–0.8 mol L⁻¹ CO₃ ²⁻ solutions, Y(III) was mainly present as the 5-coordinated complex [YCO₃·3H₂O]⁺. When the concentration of CO₃ ²⁻ was increased to 1.2 mol L⁻¹, [YCO₃·3H₂O]⁺ was converted into a 6-coordinated complex [Y(CO₃)₂·2H₂O]⁻. Further increases in CO₃ ²⁻ 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.

Over a billion tons of high-sulfur bauxite has not been utilized effectively currently in China, because the pyrite existing in the bauxite poses a range of hazards during the Bayer process. A novel idea was proposed to remove sulfur by the silicon-containing minerals in bauxite reacting with sulfur species in sodium aluminate solution to form sulfur-bearing desilication products (SDSP) for discharge with the red mud in the Bayer process. This study investigated the reaction behavior between kaolinite and different sulfur-containing ions under the simulated Bayer process conditions, elucidating the desulfurization rate variation and formation mechanism of SDSPs. The thermodynamic calculations suggest that the reaction between kaolinite and sulfur-bearing sodium aluminate solution to form SDSPs can occur spontaneously. The experimental results demonstrated that various SDSPs can be produced through the reaction of kaolinite and sulfur-containing ions in sodium aluminate solution during the simulated Bayer process, resulting in various desulfurization efficiencies, while the desulfurization process will not result in additional alkali consumption. Increasing the kaolinite dosage, extending the reaction time, and elevating the reaction temperature all contribute positively to enhancing desulfurization efficiency. Kaolinite reacted with ${\mathrm{S}}_2{\mathrm{O}}_3^{2-}$ in sodium aluminate solution to generate Na₈Al₆Si₆O₂₄S₂O₃·2H₂O, achieving a desulfurization rate exceeding 90% under optimized conditions. Under the simulated Bayer digestion process conditions at elevated temperature, the desulfurization rates of kaolinite ranked in ascending order as ${\mathrm{S}}^{2-}$ < ${\mathrm{SO}}_3^{2-}$ < ${\mathrm{SO}}_4^{2-}$ < ${\mathrm{S}}_2{\mathrm{O}}_3^{2-}$. Kaolinite reacted with ${\mathrm{SO}}_4^{2-}$ and ${\mathrm{S}}_2{\mathrm{O}}_3^{2-}$ to form cancrinite type SDSPs, and a superior desulfurization rate can be achieved. This work can provide a theoretical foundation and technological support for the efficient utilization of high-sulfur bauxite by the Bayer process.

Yb (III) shows complex behavior of coordination dissolution and precipitation in carbonate solutions, but the properties of ${\mathrm{C}\mathrm{O}}_3^{2-}$ coordination and hydration to Yb (III) in the solution have not been explicated. In this work, the dissolution rule of Yb (III) with ${\mathrm{C}\mathrm{O}}_3^{2-}$ concentration has been studied. The radial distribution function and the coordination number of ${\mathrm{C}\mathrm{O}}_3^{2-}$ and ${\mathrm{H}}_2\mathrm{O}$ 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 ${\mathrm{C}\mathrm{O}}_3^{2-}$ on Yb (III); the coordination of carbonate on Yb (III) occurs with a ${\mathrm{C}\mathrm{O}}_3^{2-}$ concentration range of 0.4~2.0 mol·${\mathrm{L}}^{-1}$. Yb (III) mainly exhibits ${[\mathrm{Y}\mathrm{b}·9{\mathrm{H}}_2\mathrm{O}]}^{3+}$ hydrated form in the aqueous solution, while, in the carbonate solution, ${[\mathrm{Y}\mathrm{b}·9{\mathrm{H}}_2\mathrm{O}]}^{3+}$ is converted into ${[\mathrm{Y}{\mathrm{b}(\mathrm{C}\mathrm{O}}_3{)}_2·5{\mathrm{H}}_2\mathrm{O}]}^{-}$ complex. ${[\mathrm{Y}{\mathrm{b}(\mathrm{C}\mathrm{O}}_3{)}_2·5{\mathrm{H}}_2\mathrm{O}]}^{-}$ 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.