Metastable Dissolution Regularity of Nd³⁺ in Na₂CO₃ Solution and Mechanism

The carbonate solution-dissolved rare earth showed some metastable chemical characteristics. In this paper, the systematic investigation of metastable dissolution regularity of Nd³⁺ in Na₂CO₃ solution was carried out. The results showed that Nd³⁺ has an instantaneous saturated solubility in Na₂CO₃ solution. When the amount of the dissolution Nd³⁺ did not reach the instantaneous saturated solubility, the solution was in a stable-state period. Once the concentration of Nd³⁺ exceeded the instantaneous saturated solubility, the solution was no longer in the metastable state and generated the neodymium double salt of carbonate precipitates rapidly. The molecular dynamics simulation of the solution in the metastable state was carried out. In high concentration Na₂CO₃ solution, dissolved Nd³⁺ had a coordination reaction with the CO₃ ^2-. Also, there was a stronger interaction between Na⁺ and CO₃ ^2-, which caused the effective concentration of free CO₃ ^2- which could react with Nd³⁺ to become lower. Thus, these reasons make the solution exhibit a metastable state. In that metastable period, the dissolved Nd³⁺ becomes steady and hard to generate the neodymium double salt of carbonate precipitates.