The Solubility of Boric Acid in Electrolyte Solutions

The solubility of boric acid [B] in LiCl, NaCl, KCl, RbCl, and CsCl was determined as a function of ionic strength (0–6 mol ⋅ kg⁻¹) at 25 ^∘C. The results were examined using the Pitzer equationwhere [B]⁰ is the concentration of boric acid in water and [B] in solution, γ_B is the activity coefficient, ν_i is the number of ions (i), λ_Bc, λ_Ba are parameters related to the interaction of boric acid with cation c and anion a, ζ_B-a−c is related to the interaction of boric acid with both cation and anion and m is the salt molality. The literature values for the solubility of boric acid in a number of other electrolytes were also examined using the same equation. The results for the 2ν_cλ_Bc+2ν_aλ_Ba term (equal to the salting coefficient k _S) were examined in terms of the ionic interactions in the solutions. The solubility of boric acid in LiCl, NaCl, and KCl solutions is not a strong function of temperature and the results can be used over a limited temperature range (5–35 ^∘C). Boric acid is soluble in the order SO₄ > NO₃ and F > Cl > Br > I in common cation solutions. In common anion salt solutions, the order is Cs > Rb > K > Na > Li > H and Ba > Sr > Ca > Mg. The results were examined using correlations of k _S with the volume properties of the ions. When direct measurements were not available, k _S and ζ_B-c−a were estimated from known values of λ_Bc and λ_Ba.The values of λ_Bc, λ_Ba, and ζ_B-a−c can be used to estimate the boric acid activity coefficients γ_B and solubility [B] in natural mixed electrolyte solutions (seawater and brines) using the more general Pitzer equation