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This paper reports the results of the investigations carried out in synthetic sea water at different salinities for different classes of polycarboxylic acids. The investigations can be summarized as follows: (a) Determination of the protonation constants in such multicomponent solution in a salinity range 15 ≤ S ≤ 45, at t = 25 °C, for the linear dicarboxylic acids HOOC-(CH2) n –COOH (0 ≤ n ≤ 8), and aromatic polycarboxylic acids (o-phthalic and 1,2,4-benzenetricarboxylic acids). For malonic, succinic, 1,2,3-benzenetricarboxylic, and 1,2,3,4-benzenetetracarboxylic acids, investigations were also carried out at t = 10 and 37 °C; (b) Determination of the total and intrinsic solubility (S T and S 0, respectively) of the linear dicarboxylic acids HOOC-(CH2) n -COOH (0 ≤ n ≤ 8), o-phthalic, 1,2,4-benzenetricarboxylic acids at t = 25 °C and 15 ≤ S ≤ 45, and calculation of the corresponding Setschenow parameters and activity coefficients; (c) Modeling the dependence of the experimental and literature protonation constants of the polycarboxylic acids on salinity, acid concentration, temperature, and number of the methylene groups in the molecules by means of new empirical equations; (d) Determination of the specific interaction parameters in synthetic sea water of the ionic species of the acids by means of the specific ion interaction theory and Pitzer models; (e) Determination of the protonation constant of the anion A1.117− of the single salt BA at different salinities and temperatures; (f) Determination and modeling in dependence of the salinity of the ΔH/kJ mol−1 of protonation of the linear dicarboxylic acids and of the A1.117− anion, by means of a Debye-Huckel type equation; (g) Determination of the complex formation constants (log β BpLHi) between the cation B1.117+ and the different deprotonated species of the carboxylic acids at different salinities and temperatures. Independent of the thermodynamic aqueous properties determined, a significant dependence of these parameters (log β i H , log β BpLHi, ΔH/kJ mol−1 of protonation, S T and S 0) on the ionic medium, salinity, and temperature was observed. Moreover, the huge number of data collected allowed us to propose some empirical equations to model/predict the behavior of these classes of O-donor ligands in a multicomponent solution such as synthetic sea water.

In this paper, new information on physical and chemical properties of the widely used nanostructured Halloysite mineral are reported. Given that the Halloysite has a tubular structure formed by a variable number of wrapped layers containing Si-OH and Al-OH groups, their proton binding affinity was measured at different ionic strengths and ionic media by means of potentiometric measurements in heterogeneous phase. One protonation constant for the Si-OH groups and two for the Al-OH groups were determined. The protonation constant values increase with increasing of the ionic strength in all the ionic media. This suggests that the presence of a background electrolyte stabilizes the protonated species through the formation of weak complexes between ions of the supporting electrolytes and the protonated species. Ten weak species were determined with different stoichiometry. It was shown that the interactions do not depend on the nature of the supporting electrolytes but on the charge. The surface charge of Halloysite was estimated by ζ potential measurements as a function of pH, and the values obtained are consistent with the nanotubes ionization predicted by using the protonation constants for the Si-OH and Al-OH groups. The total solubility of the Halloysite nanotubes, was also determined in NaCl aqueous solution. These measurements showed that the solubility slightly increases with increasing ionic strength and contact time between Halloysite and NaCl solution. Goodness-of-fit (GOF) criteria were used to test the application of these models with good results. The obtained results confirm that the behavior of Halloysite in water is strictly correlated to the experimental conditions of the aqueous suspension (e.g., pH, ionic strength, and ionic media). The thermodynamic data here reported are of main importance in the several applications where is exploited the charge separation between the inner and outer surfaces of this nanotubular material.