Journal article
Chemical speciation of environmentally significant metals with inorganic ligands. Part 4: The Cd2+ + OH–, Cl–, CO32–, SO42–, and PO43– systems (IUPAC Technical Report)
Pure and Applied Chemistry, Vol.83(5), pp.1163-1214
2011
Abstract
The numerical modeling of Cd-II 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 log(10) beta(p,q,r) valid at I-m = 0 mol kg(-1) and 25 degrees C (298.15 K), along with the equations and empirical reaction ion interaction coefficients, Delta epsilon, required to calculate log(10)beta(p),(,q,r) values at higher ionic strengths using the Bronsted-Guggenheim-Scatchard specific ion interaction theory (SIT). Values for the corresponding reaction enthalpies, Delta H-r, are reported where available. Unfortunately, with the exception of the Cd-II-chlorido system and (at low ionic strengths) the Cd-II-sulfato system, the equilibrium reactions for the title systems are relatively poorly characterized.
In weakly acidic fresh water systems (-log(10){[H+]/c degrees} < 6), in the absence of organic ligands (e. g., humic substances), Cd-II speciation is dominated by Cd2+(aq), with CdSO4(aq) as a minor species. In this respect, Cd-II is similar to Cu-II [2007PBa] and Pb-II [2009PBa]. However, in weakly alkaline fresh water solutions, 7.5 < -log(10) {[H+]/c degrees} < 8.6, the speciation of Cd-II is still dominated by Cd2+(aq), whereas for Cu-II [2007PBa] and Pb-II [2009PBa] the carbonato-species MCO3(aq) dominates. In weakly acidic saline systems (-log(10) {[H+]/c degrees} < 6; -log(10) {[Cl-]/c degrees} < 2.0) the speciation is dominated by CdCln(2-n)+ complexes, (n = 1-3), with Cd2+(aq) as a minor species. This is qualitatively similar to the situation for Cu-II and Pb-II. However, in weakly alkaline saline solutions, including seawater, the chlorido-complexes still dominate the speciation of Cd-II because of the relatively low stability of CdCO3(aq). In contrast, the speciation of Cu-II [2007PBa] and Pb-II [2009PBa] in seawater is dominated by the respective species MCO3(aq).
There is scope for additional high-quality measurements in the Cd2+ + H+ + CO32- system as the large uncertainties in the stability constants for the Cd2+-carbonato complexes significantly affect the speciation calculations.
Details
- Title
- Chemical speciation of environmentally significant metals with inorganic ligands. Part 4: The Cd2+ + OH–, Cl–, CO32–, SO42–, and PO43– systems (IUPAC Technical Report)
- Authors/Creators
- K.J. Powell (Author/Creator) - University of CanterburyP.L. Brown (Author/Creator) - Rio Tinto (Australia)R.H. Byrne (Author/Creator) - University of South Florida St. PetersburgT. Gajda (Author/Creator) - University of DebrecenG. Hefter (Author/Creator) - Murdoch UniversityA-K Leuz (Author/Creator) - Swiss Federal Nuclear Safety InspectorateS. Sjöberg (Author/Creator) - Umeå UniversityH. Wanner (Author/Creator) - Swiss Federal Nuclear Safety Inspectorate
- Publication Details
- Pure and Applied Chemistry, Vol.83(5), pp.1163-1214
- Publisher
- International Union of Pure and Applied Chemistry
- Identifiers
- 991005543222707891
- Copyright
- © 2011 IUPAC
- Murdoch Affiliation
- School of Chemical and Mathematical Science
- Language
- English
- Resource Type
- Journal article
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- Collaboration types
- Industry collaboration
- Domestic collaboration
- International collaboration
- Citation topics
- 2 Chemistry
- 2.22 Inorganic & Nuclear Chemistry
- 2.22.1278 Stability Constants
- Web Of Science research areas
- Chemistry, Multidisciplinary
- ESI research areas
- Chemistry