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

Ryan J. Woosley, Frank J. Millero

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


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°C in dilute solutions and 0 to 100°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 The correlation at higher temperatures is a result of a similar relationship between the enthalpies of the free ions and complexes 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. 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).

Original languageEnglish (US)
Pages (from-to)317-324
Number of pages8
JournalAquatic Geochemistry
Issue number3
StatePublished - Jun 2010


  • Divalent, trivalent, and quadrivalent metals
  • Hydrolysis constants

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology


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