SOLUBILITY OF NAND(CO3)(3)CENTER-DOT-6H(2)O(C) IN CONCENTRATED NA2CO3AND NAHCO3 SOLUTIONS

NaNd(CO3)(2) . 6 H2O(c) was identified to be the final equilibrium sol id 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(CO3) (2) . 6 H2O(c) or Nd-2(CO3)(3) . xH(2)O(s) as initial solids. A thermo dynamic model, based on Fitter's specific ion-interaction approach, wa s developed to interpret the solubility of NaNd(CO3)(2) . 6 H2O(c) as functions of sodium carbonate and sodium bicarbonate concentrations. I n this model, the solubility data of NaNd(CO3)(2) . 6 H2O(c) were expl ained by assuming the formation of NdCO3+, Nd(CO3)(2)(-) and Nd(CO3)(3 )(3-) species and invoking the specific ion interactions between Na+ a nd Nd(CO3)(3)(3-). Ion interaction parameters for Na+-Nd(CO3)(3)(3-) w ere developed to fit the solubility data. Based on the model calculati ons, Nd(CO3)(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(CO3)(2) . 6 H2O solubility product (NaNd(C O3)(2) . 6 H2O(c) = Na+ + Nd3+ + 2 CO32- + 6 H2O) was calculated to be -21.39. This model also provided satisfactory interpretation of the s olubility data of the analogous Am(III) system in less concentrated ca rbonate and bicarbonate solutions.