Formation Quotients of Aluminum Sulfate Complexes in NaCF₃SO₃ Media at 10, 25, and 50 °C from Potentiometric Titrations Using a Mercury/Mercurous Sulfate Electrode Concentration Cell

Abstract

Mercury/mercurous sulfate electrode concentration cells (with liquid junction) are employed in this study to determine the formation constants of aluminum sulfate complexes, with the principal advantage that the change in the free sulfate concentration is measured directly without the need to know the standard potential of the electrode. Potentiometric titrations were conducted at temperatures of 10, 25, and 50 degrees C and ionic strengths of approximately 0.3, 0.5, and 1.0 molal in aqueous solutions of the inert 1:1 electrolyte sodium trifluoromethanesulfonate (NaTr). Stoichiometric molal formation quotients Q1 and Q2, respectively, for the reactions Al3+(aq) + SO4(2-)(aq) AlSO4+(aq) and Al3+(aq) + 2SO4(2-)(aq) <= >Al(SO4)2-(aq) were determined. The values of log Q1 obtained from this work in NaTr media at ionic strengths of 0.3 and 1.0 mol x kg(-1) and 50 degrees C (1.72 +/- 0.08 and 1.35 +/- 0.06, respectively) are in excellent agreement with the values (1.71 +/- 0.2 and 1.32 +/- 0.1) determined in NaCl media from the recent potentiometric study conducted in the same laboratory using a hydrogen electrode concentration cell by Ridley et al. (Ridley, M. K.; Wesolowski, D. J.; Palmer, D. A.; Kettler, R. M. Geochim. Cosmochim. Acta 1999, 62, 459-472). The value of log Q2 (2.05 +/- 0.05) in 1.0 mol x kg(-1) from this work is smaller than the value reported by Ridley et al. (2.6 +/- 0.5) but within the combined experimental error. Empirical isothermal equations are presented to permit calculation of the equilibrium quotients as a function of ionic strength (0-1 mol x kg(-1)), giving log K1 and log K2 values at 25 degrees C and infinite dilution of 3.84 +/- 0.12 and 5.58 + 0.09, respectively. The value for log K1 obtained in this study at 25 degrees C is bracketed within experimental uncertainty by values reported by Kryzhanovskii et al. (Kryzhanovskii, M. M.; Volokhov, Y. A.; Pavlov, L. N.; Eremin, N. I.; Mironov, V. E Zh. Prikl. Khim. 1971, 44,476-479) and Nishide and Tsuchiya (Nishide, T.; Tsuchiya, R. Bull. Chem. Soc. Jpn. 1965, 38, 1398-1400), namely, 3.89 and 3.73, respectively. All other literature values for the first aluminum sulfate association constant are considerably lower than these results, which is also true for the second association constant, although there are few experimental data available for the latter. Empirical equations are also presented for calculating values of log Q1 and log Q2 from 0 to 1 molal ionic strength and from 10 to 125 degrees C, spanning the range of most environmental conditions at which these reactions are important.

A spectrophotometric study of neodymium(III) complexation in sulfate solutions at elevated temperatures

“…It is worth noting that the formation constants determined in this study are similar to those recommended for Al-SO 4 complexes by Ridley et al (1999) and Xiao et al (2002). However, although the values of the formation constants for Al-and Nd-sulfate complexes are nearly identical at low temperatures, the temperature dependencies differ appreciably (Fig.…”

“…A comparison of the values of log K s obtained in this study with those estimated theoretically by Wood (1990b). β 1 for Al (Xiao et al, 2002) β 2 for Al (Xiao et al, 2002) K s for Al (Xiao et al, 2002) β 1 for Nd (this study) β 2 for Nd (this study) K s for Nd (this study)…”

Occurrence of polymerized silicic acid and aluminum species in two forest soil solutions with different acidity

“…The SUPCRT92 program enables calculation of consistent values for the stability constants of a set of reactions based on the HKF formalism (Johnson et al, 1992). The formation constants determined by Xiao et al (2002) are used for the monomeric Al-SO 4 . The work by Pokrovski et al (1998) was considered for the logK of the negatively charged monomeric Al-Si complexes, and these in Nordstrom and May (1989) were used for the AlF 5 2− , AlF 6 3− and Al-phosphate species.…”

“…F − , SO 4 2− , H 4 SiO 4°) and organic ligands (e.g. Tipping, 1998;Tagirov and Schott, 2001;Xiao et al, 2002). The binding of Al by organics strongly depends on the pH, the concentration of ligands, and on their affinity towards metalbinding.…”

Comment on: “The dissolution rates of gibbsite in the presence of chloride, nitrate, silica, sulfate and citrate in open and closed systems at 20°C” by M. Dietzel and G. Böhme

“…Dietzel and Böhme also failed to cite our recent study (Xiao et al, 2002) of the formation constants of aluminum sulfate complexes via the reactions:…”