Solubility of NaNd(CO3)2.6H2O(c) in Mixed Electrolyte (Na-Cl-CO3-HCO3) and Synthetic Brine Solutions

Abstract

Experiments were conducted to evaluate the solubility of neodyrrrium(III) in mixed electrolyte solutions (Nd3+-Na+-Cl−-CO3 2−-HCO3 −-H2O) and in two synthetic brines under different partial pressures of CO2. The stable solid phase in solutions containing concentrated NaCl (2 m and 4 m)/Na2CO3 (0.1 to 2.0 m) and NaCl (2 m)/NaHCO3 (0.1 to 1.0 m) was identified by X-ray diffraction to be NaNd(CO3)2.6H2O(c), which is the same equilibrium solid phase previously observed in solutions of single electrolytes (Na2CO3 or NaHCO3 in the absence of NaCl). Using Pitzer’s specific ion-interaction approach, ternary ion interaction parameters were developed for Na+-Cl−-Nd(CO3)3 3− and incorporated into the previous data base for the single electrolyte, non-chloride systems. The resulting model developed from these experiments provided satisfactory interpretation of the concentration of neodymium in the mixed electrolyte solutions of this study. Model predictions were tested against the experimental measurements of the solubility of Nd(III) in two synthetic brines equilibrated with carbon dioxide at partial pressures of PCO2 = 10−3.5 atm and 1 atm. The model predictions of the total neodymium concentration in these two brines agree with the experimental results showing deviations less than one order of magnitude. In addition, the model provides a good prediction of the solubility of NaAm(CO3)2(c) in 5.6 m NaCl solution equilibrated with carbon dioxide over a wide range of carbonate concentrations.