Solubility of NaNd(CO₃)² · 6 H₂O(c) in Concentrated Na2C03 and NaHC03 Solutions

Abstract

NaNd(C0 3 ) 2 · 6 H 2 0(c) was identified to be the final equilibrium solid phase in suspensions containing concentrated sodium carbonate (0.1 to 2.0 M) and sodium bicarbonate (0.1 to 1.0 M), with either NaNd(C0 3 ) 2 · 6 H 2 0(c) or Nd 2 (C0 3 ) 3 · xH 2 0(s) as initial solids. A thermodynamic model, based on Pitzer's specific ion-interaction approach, was developed to interpret the solubility of NaNd(C0 3 ) 2 · 6 H 2 0(c) as functions of sodium carbonate and sodium bicarbonate concentrations. In this model, the solubility data of NaNd(C0 3 ) 2 · 6 H 2 0(c) were explained by assuming the formation of NdC0 3 + , Nd(C0 3 ) 2 and Nd(C0 3 )r species and invoking the specific ion interactions between Na + and Nd(C0 3 )5". Ion interaction parameters for Na + -Nd(C0 3 )l~ were developed to fit the solubility data. Based on the model calculations, Nd(C0 3 ) 3~ was the predominant aqueous neodymium species in 0.1 to 2 M sodium carbonate and 0.1 to 1 M sodium bicarbonate solutions. The logarithm of the NaNd(C0 3 ) 2 · 6 H 2 0 solubility product (NaNd(C0 3 ) 2 · 6 H 2 0(c) = Na + + Nd 3+ + 2 COI" + 6 H 2 0) was calculated to be -21.39. This model also provided satisfactory interpretation of the solubility data of the analogous Am(III) system in less concentrated carbonate and bicarbonate solutions.

Evidence of different stoichiometries for the limiting carbonate complexes across the lanthanide(III) series: A capillary electrophoresis‐mass spectrometry study

“…3). The CE-ICP-MS measurements show that Dy is the first lanthanide for which log 10 K Na2CO3 , 0.1 6 0.6) are consistent with the log 10 K 4 data published for Ce [13], Nd [4], Eu and Gd [12] extrapolated (using log 10 K 4;Gd determined from the raw results of Faucherre et al [12] by Vercouter et al [5]) to 0.5 mol L -l Na 2 CO 3 background electrolyte with the SIT formula. For the heaviest (smallest) lanthanides.…”

“…Tetracarbonate complexes were proposed for Nd(III) [18,20], Sm(III) [19], Ho(III) [21] according to single-crystal X-ray diffraction. Absorbance spectra of Nd(III) in concentrated guanidinium carbonate aqueous solutions were in fair agreement with diffuse reflectance spectra of the Nd(CO 3 ) 4 -(H 2 O) 52 stoichiometry in the solid compound [18]. Consequently, NdðCO 3 Þ 5À 4 was considered to be the most probable stoichiometry in solution, while it could be partially dissociated.…”

“…However, the stoichiometry of the aqueous carbonate limiting complex (complex with maximum number of ligands) of lanthanides (Ln) and actinides (An) is still discussed, even after the well-accepted Nuclear Energy Agency review of Am published thermochemical data [1,2]. Indeed, two stoichiometries have been reported for their limiting complexes: MðCO 3 Þ 3À 3 [3][4][5][6][7][8][9] and MðCO 3 Þ 5À 4 [3,[9][10][11][12][13][14][15][16]. The latter stoichiometry has been reported for light lanthanides only, since the lanthanides heavier than Tb had never been evidenced as MðCO 3 Þ 5À 4 complexes.…”

“…The latter stoichiometry has been reported for light lanthanides only, since the lanthanides heavier than Tb had never been evidenced as MðCO 3 Þ 5À 4 complexes. Solubility appeared to be a reliable method to determine the stoichiometries of the limiting complexes in concentrated carbonate solutions [4,5,7,8,12,13].…”

“…Indeed, NaLn(CO 3 ) 2 , xH 2 O(s) is the thermodynamically stable solid-phase controlling solubility in concentrated sodium carbonate solutions [4,12,13,17]. These solid compounds are in equilibria with the carbonate limiting complexes using high carbonate concentrations.…”