Measurement of Specific Heat Capacity of NaBO2 (aq) Solution and Thermodynamic Modeling of NaBO2 + H2O, NaBO2 + NaCl + H2O, and NaBO2 + Na2SO4 + H2O Systems

The specific heat capacity of NaBO2(aq) solution was determined using a Calvet-type calorimeter at a temperature from 288.15 to 338.15 K and at a concentration from about 0.25 mol.k(-1) H2O to near room temperature solubility limit. Combining these specific heat capacity data and thermodynamic and solid-liquid equilibrium data reported in the literature, a temperature-dependent thermodynamic model was developed for the NaBO2 + H2O system based on Pitzer-Simonson-Clegg activity coefficient equations. The model represents all of the properties over a wide temperature and concentration ranges. Combining the binary models of NaCl + H2O and Na2SO4 + H2O systems published in the previous studies of our group, multitemperature thermodynamic models of the NaBO2 + NaCl + H2O and NaBO2 + Na2SO4 + H2O systems were constructed. These ternary models reproduce the experimental solubility isotherms reported in the literature in general, but some significant inconsistency is still present. More accurate solubility data for these ternary systems at various temperatures are urgent.