Chemical speciation of environmentally significant metals with inorganic ligands. Part 5: The Zn2+ + OH-, Cl-, CO32-, SO42-, and PO43-systems (IUPAC Technical Report)

Kipton J. Powell, Paul L. Brown, Robert H. Byrne, Tamas Gajda, Glenn Hefter, Ann Kathrin Leuz, Staffan Sjöberg, Hans Wanner

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The numerical modeling of ZnII speciation amongst the environmental inorganic ligands Cl-, OH-, CO32-, SO42-, and PO43-requires reliable values for the relevant stability (formation) constants. This paper compiles and provides a critical review of these constants and related thermodynamic data. It recommends values of log10βp,q,r° valid at Im = 0 mol·kg-1 and 25 °C (298.15 K), and reports the empirical reaction ion interaction coefficients, Δ∈required to calculate log10βp,q,r values at higher ionic strengths using the Brønsted-Guggenheim-Scatchard specific ion interaction theory (SIT). Values for the corresponding reaction enthalpies, ΔrH, are reported where available. There is scope for additional high-quality measurements for the Zn2+ + H+ + CO32-system and for the Zn2+ + OH-and Zn2+ + SO42-systems at I > 0. In acidic and weakly alkaline fresh water systems (pH <8), in the absence of organic ligands (e.g., humic substances), ZnII speciation is dominated by Zn2+(aq). In this respect, ZnII contrasts with CuII and PbII (the subjects of earlier reviews in this series) for which carbonato-and hydroxido-complex formation become important at pH > 7. The speciation of ZnII is dominated by ZnCO3(aq) only at pH > 8.4. In seawater systems, the speciation at pH = 8.2 is dominated by Zn2+(aq) with ZnCl+, Zn(Cl)2(aq), ZnCO3(aq), and ZnSO4(aq) as minor species. This behaviour contrasts with that for CuII and PbII for which at the pH of seawater in equilibrium with the atmosphere at 25 °C (log10 {[H+]/c°} ≈ 8.2) the MCO3(aq) complex dominates over the MCln(2-n)+ species. The lower stability of the different complexes of ZnII compared with those of CuII, PbII, and CdII is also illustrated by the percentage of uncomplexed M2+ in seawater, which is ca. 55, 3, 2, and 3.3% of [MII]T, respectively.

Original languageEnglish
Pages (from-to)2249-2311
Number of pages63
JournalPure and Applied Chemistry
Issue number12
Publication statusPublished - Dec 18 2013



  • Chemical speciation
  • Environmental chemistry
  • IUPAC Analytical Chemistry Division
  • Inorganic ligands
  • Stability constants
  • Zinc

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)

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