Thermodynamic modeling of the solubility of boric acid in the systems boric acid + lithium sulfate + water, boric acid + sodium sulfate + water and boric acid + potassium sulfate + water at 293.15–313.15 K

• Reliable data of solubility of boric acid in sodium sulfate aqueous solutions is reported.
• A simple and suitable model for estimating the solubility of boric acid is presented.
• Sodium sulfate and potassium sulfate concentration increasing raise solubility of boric acid.
• Lithium sulfate concentration increasing drops solubility of boric acid.
• The temperature does not increase the salt effect on the solubility.

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 3.3795) mol kg−1 H2O.The results were represented using an equation based on Pitzer model for the interactions of nonelectrolytes with electrolytes in aqueous solutions, given by Chanson and Millero (2006) [18]. The model parameter was estimated and validated estimating the solubility of boric acid in lithium sulfate, sodium sulfate and potassium sulfate aqueous solutions at different temperatures and salt concentrations. The model represented satisfactorily the data for the systems (SD = 0.033 mol kg−1 H2O for H3BO3 + Na2SO4 + H2O, SD = 0.020 mol kg−1 H2O for H3BO3 + Li2SO4 + H2O and SD = 0.030 mol kg−1 H2O for H3BO3 + K2SO4 + H2O). The model parameters are valid to maximum concentration of the salts, 3.380 mol kg−1 for Na2SO4, 3.149 mol kg−1 for Li2SO4 and 1.245 mol kg−1 for K2SO4 from 293.15 K to 313.15 K.Based on the results it was determined that lithium sulfate is a precipitant agent for boric acid and its behavior is attributed to the salting out effect of Li+ ion; sodium and potassium sulfates increase the boric acid solubility; this salting in effect is due to the presence of Na+ and K+ ions. The presence of these salts can be unfavorable for the crystallization of boric acid due to the increase of solubility which 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, it was found that effect of these ions on the decreasing of the solubilty of boric acid in aqueous sulfate solutions follows the order: Li+ > Na+ > K+, which can be attributed to the increase of their ionic radii, coordinated with 6 water molecules therefore the capacity to form hydration shells.

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