Metastable Dissolution Regularity of Nd³⁺ in Na₂CO₃ Solution and Mechanism

Abstract

The carbonate solution-dissolved rare earth showed some metastable chemical characteristics. In this paper, the systematic investigation of metastable dissolution regularity of Nd 3+ in Na 2 CO 3 solution was carried out. The results showed that Nd 3+ has an instantaneous saturated solubility in Na 2 CO 3 solution. When the amount of the dissolution Nd 3+ did not reach the instantaneous saturated solubility, the solution was in a stable-state period. Once the concentration of Nd 3+ 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 Na 2 CO 3 solution, dissolved Nd 3+ had a coordination reaction with the CO 3 2– . Also, there was a stronger interaction between Na + and CO 3 2– , which caused the effective concentration of free CO 3 2– which could react with Nd 3+ to become lower. Thus, these reasons make the solution exhibit a metastable state. In that metastable period, the dissolved Nd 3+ becomes steady and hard to generate the neodymium double salt of carbonate precipitates.

Maintenance of the Metastable State and Induced Precipitation of Dissolved Neodymium (III) in an Na2CO3 Solution

“…Compared with the blank neodymium solution spectrum, it is worth noting that the characteristic peaks of neodymium obtained from the NaCl/Na2CO3 solutions with dissolved neodymium were slightly red-shifted from the initial 347 and 354 nm wavelengths due to the high alkalinity of the NaCl/Na2CO3 mixed electrolyte solution. There were also neodymium characteristic peaks at 524 and 575 nm wavelengths in the UV-vis spectrum of the neodymium-dissolving solution, as in our previously results [19]. In addition, a new peak with higher intensity was observed at 583 nm.…”

“…There were also neodymium characteristic peaks at 524 and 575 nm wavelengths in the UV-vis spectrum of the neodymium-dissolving solution, as in our previously results [19]. In addition, a new peak with higher intensity was observed at 583 nm.…”

“…In order to investigate the mechanism of the maintenance of the metastable state by the additional NaCl, molecular dynamic (MD) calculations were carried out. The construction and optimization of the solution components were consistent with our previous study [19]. The model of the solution with the addition of 0.5 mol•L −1 NaCl (with the better metastable condition), and the corresponding blank solution (Na 2 CO 3 /NaCl solution with the only additional water) was also established by using the Amorphous Cell module.…”

“…Other equipment used in experiments is shown in Table 2. Following on from our previous research [19], the effect of additional NaCl on the maintenance of the metastable state of a solution of dissolved Nd 3+ was investigated. The neodymium concentration in 2 mol•L −1 Na 2 CO 3 solution was controlled at 2.621 g•L −1 .…”

“…A good and feasible green method to separate rare earths is by using the metastable state of the carbonate solution which dissolves them. In our previous study [19], a series of experiments on metastable states was carried out by choosing neodymium as an example of rare earth elements. Our results indicated that neodymium dissolved in a sodium carbonate solution exhibited some metastable properties.…”