The apparent molar heat capacities of LiBO 2 (aq), NaBO 2 (aq), KBO 2 (aq), Na 2 B 4 O 7 (aq) and K 2 B 4 O 7 (aq) solutions at molalities from 0.01 to 2.6 mol·kg −1 , and at temperatures T = (298.12, 313.13 and 328.14) K have been determined using a Picker flow calorimeter built in this work. Further, the standard heat capacities of these solutes were derived from the experimental data by extrapolation to infinite dilution using the Pitzer ion-interaction model. The group contribution method is used to calculate the standard molar heat capacities of tetraborate ion in three equilibria for different assumptions, among which the prediction on the assumption that the standard molar heat capacity of reaction for the association reaction is zero is the most reasonable, and the results are in good agreement with the experimental data.
Fei Yuan,Hua Li,Long Li,Yafei Guo,Shiqiang Wang,Tianlong Deng
Considering the significance of fundamental phase equilibrium data in resource exploitation from salt lake brines, the solid–liquid phase equilibria of the ternary system (KBO2 + K2SO4 + H2O) at 288.15, 308.15 K, and 0.1 MPa were investigated using the isothermal dissolution method. Along this line, the solubilities and physicochemical properties of densities were experimentally determined. Based on the experimental data, phase diagrams and the related physicochemical property diagrams against composition were plotted. It was found that there are one invariant point, two univariate solubility curves, and two crystalline regions corresponding to potassium metaborate hydrate (KBO2·1.33H2O) and arcanite (K2SO4) in the ternary phase diagrams at 288.15 and 308.15 K. In addition, they belong to the hydrate type I and neither double salt nor solid solution was formed. The distributive behaviors of density against the concentration of KBO2 in the equilibrium solution at two temperatures were similar. Moreover, the theoretical values of density were calculated, which were found to be consistent with the experimental values, further demonstrating the accuracy and reliability of this work.
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