Thermodynamics Research Center / ThermoML | Fluid Phase Equilibria

ABSTRACT

In this contribution the experimental solubility of boric acid in sodium sulfate aqueous solution was measured at different temperatures from (293.15 to 313.15)K, and Na2SO4 concentrations ranging from (0 to 3.3242) mol*kg 1 H2O. The results were represented using an equation based on Pitzer model. The model was validated estimating the solubility of boric acid in lithium sulfate, and sodium sulfate aqueous solutions at different temperatures and salt concentrations. The model represented satisfactorily the data for both systems (SD=0.02 mol*kg-1 H2O for H3BO3+Na2SO4+H2O and SD=0.019 mol*kg-1 H2O for H3BO3+Li2SO4+H2O). The model parameters are valid to maximum concentration of the salts, 3.4 mol*kg-1for Na2SO4 and 3.3 mol*kg-1for Li2SO4, and from 293.15 K to 313.15 K. Based on the results it was determined that the lithium sulfate is a precipitant agent for boric acid and that its behavior is attributed to the salting out effect of Li+ ion, and sodium sulfate increases the boric acid solubility, this salting in effect is due to the presence of Na+ ion. The presence of this salt can unfavorable for the crystallization of boric acid, due to decreases the supersaturation therefore the yield of the process. Comparing the parameters for the system H3BO3+Na2SO4+H2O, H3BO3+Li2SO4+H2O and H3BO3+K2SO4+H2O was found that effect of the ions, in aqueous sulfate solutions follows this order: Li greater than Na greater than K, which can be attributed to the increase of their ionic radii, coordinated with 6 water molecules therefore the capacity to form hydration shells.