The Hydrolysis of Al(III) in NaCl solutions: A Model for M(II), M(III), and M(IV) Ions

作者：Woosley Ryan J; Millero Frank J^*

来源：Aquatic Geochemistry, 2010, 16(3): 317-324.

DOI：10.1007/s10498-009-9075-2

• Hydrolysis constants
• Divalent
• trivalent
• and quadrivalent metals

Understanding the identity and stability of the hydrolysis products of metals is required in order to predict their behavior in natural aquatic systems. Despite this need, the hydrolysis constants of many metals are only known over a limited range of temperature and ionic strengths. In this paper, we show that the hydrolysis constants of 31 metals [i.e. Mn(II), Cr(III), U(IV), Pu(IV)] are nearly linearly related to the values for Al(III) over a wide range of temperatures and ionic strengths. These linear correlations allow one to make reasonable estimates for the hydrolysis constants of ? 2, ? 3, and ? 4 metals from 0 to 300 degrees C in dilute solutions and 0 to 100 degrees C to 5 m in NaCl solutions. These correlations in pure water are related to the differences between the free energies of the free ion and complexes being almost equal
Delta G degrees (Al(3+)) - Delta G degrees (Al(OH)(j)((3-j))) congruent to Delta G degrees(M(n+)) - Delta G degrees(M(OH)(j)((n-j)))
The correlation at higher temperatures is a result of a similar relationship between the enthalpies of the free ions and complexes
Delta H degrees (Al(3+)) - Delta H degrees (Al(OH)(j)((3-j))) congruent to Delta H degrees(M(n+)) - Delta H degrees(M(OH)(j)((n-j)))
The correlations at higher ionic strengths are the result of the ratio of the activity coefficients for Al(III) being almost equal to that of the metal.
gamma(M(n+))/gamma(M(OH)(j)(n) (j)) congruent to gamma(Al(3+))/gamma(Al(OH)(j)(3) (j))
The results of this study should be useful in examining the speciation of metals as a function of pH in natural waters (e.g. hydrothermal fresh waters and NaCl brines).

• 出版日期2010-6