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| 2. |
- Powell, Kipton J, et al.
(author)
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Chemical speciation of environmentally significant metals : an IUPAC contribution to reliable and rigorous computer modelling
- 2015
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In: Chemistry International. - : Walter de Gruyter. - 0193-6484 .- 1365-2192. ; 37:1, s. 15-19
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Journal article (peer-reviewed)abstract
- The mobility and bioavailability of metal ions in natural waters depend on their chemical speciation, which involves a distribution of the metal ions between different complex (metal-ligand) species, colloid-adsorbed species and insoluble phases, each of which may be kinetically labile or inert. For example, in fresh water the metal ions are distributed among organic complexes (e.g., humates), colloids (e.g., as surface-adsorbed species on colloidal phases such as FeOOH), solid phases (e.g., hydroxide, oxide, carbonate mineral phases), and labile complexes with the simple inorganic anionic ligands commonly present in natural waters (e.g., for ZnII, the aqueous species, Zn2+, ZnOH+, Zn(OH)2(aq), Zn2OH3+, ZnSO4(aq), ZnCO3(aq)…).
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| 3. |
- Powell, Kipton J, et al.
(author)
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Chemical speciation of environmentally significant metals with inorganic ligands. Part 3: The Pb2+ + OH–, Cl–, CO32–, SO42–, and PO43– systems (IUPAC Technical Report)
- 2009
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In: Pure and Applied Chemistry. - 0033-4545 .- 1365-3075. ; 81:12, s. 2425-76
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Journal article (peer-reviewed)abstract
- Complex formation between PbII and the common environmental inorganic ligands, Cl–, OH–, CO32–, SO42–, and PO43–, can be significant in natural waters with low concentrations of organic matter. Numerical modeling of the speciation of PbII amongst these inorganic ligands requires reliable values for the relevant stability (formation) constants. This paper provides a critical review of such constants and related thermodynamic data. It recommends values of log10 βp,q,r° valid at Im = 0 mol kg–1 and 25 °C (298.15 K), along with the equations and empirical coefficients required to calculate log10 βp,q,r values at higher ionic strengths using the Brønsted–Guggenheim–Scatchard specific ion interaction theory (SIT). Some values for reaction enthalpies, ΔrH, are also reported. In weakly acidic fresh water systems (–log10 {[H+]/c°} < 6), the speciation of PbII is similar to that of CuII. In the absence of organic ligands, PbII speciation is dominated by Pb2+(aq), with PbSO4(aq) as a minor species. In weakly alkaline solutions, 8.0 < –log10 {[H+]/c°} < 9.0, the speciation is dominated by the carbonato species PbCO3(aq) and Pb(CO3)22–. In weakly acidic saline systems (–log10 {[H+]/c°} < 6), the speciation is dominated by PbCln(2–n)+ complexes, (n = 0–3), with Pb2+(aq) as a minor species. In this medium (and in seawater), the speciation contrasts with that of CuII because of the higher stability of the Pb2+-chlorido- complexes. In seawater at –log10 {[H+]/c°} = 8.2, the calculated speciation is less well defined, although it is clearly dominated by the uncharged species PbCO3(aq) (41 % of [Pb]T) with a significant contribution (16 %) from Pb(CO3)Cl– and minor contributions (5–10 %) from PbCln(2–n)+, (n = 0–3) and Pb(CO3)22–. The uncertainty in calculations of PbII speciation in seawater arises from (a) the large uncertainty in the stability constant for the apparently dominant species PbCO3(aq), (b) the reliance on statistical predictions for stability constants of the ternary species Pb(CO3)Cl– and Pb(CO3)OH–, and (c) the uncertainty in the stability constant for PbCl42–, the available value being considered "indicative" only. There is scope for additional detailed high-quality measurements in the Pb2+ + CO32– + Cl– system.
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| 4. |
- Powell, Kipton J., et al.
(author)
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Chemical speciation of environmentally significant metals with inorganic ligands. Part 5: The Zn2+ + OH–, Cl–, CO32–, SO42–, and PO43– systems (IUPAC Technical Report)
- 2013
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In: Pure and Applied Chemistry. - 0033-4545 .- 1365-3075. ; 85:12, s. 2249-2311
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Journal article (peer-reviewed)abstract
- 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 log10 βp,q,r° valid at Im = 0 mol·kg–1 and 25 °C (298.15 K), and reports the empirical reaction ion interaction coefficients, ∆ε, required to calculate log10 βp,q,r values at higher ionic strengths using the Brønsted–Guggenheim–Scatchard specific ion interaction theory (SIT). Values for the corresponding reaction enthalpies, ∆rH, 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.
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| 5. |
- Powell, Kipton J, et al.
(author)
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Chemical speciation of environmentally significant metals with inorganic ligands : Part 4: The Cd2+ + OH–, Cl–, CO32–, SO42–, and PO43– systems (IUPAC Technical Report)
- 2011
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In: Pure and Applied Chemistry. - 0033-4545 .- 1365-3075. ; 83:5, s. 1163-1214
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Journal article (peer-reviewed)abstract
- The numerical modeling of CdII 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 log10 βp,q,r° valid at Im = 0 mol kg–1 and 25 °C (298.15 K), along with the equations and empirical reaction ion interaction coefficients, ∆ε , required to calculate log10 βp,q,r values at higher ionic strengths using the Brønsted–Guggenheim–Scatchard specific ion interaction theory (SIT). Values for the corresponding reaction enthalpies, ∆rH, are reported where available. Unfortunately, with the exception of the CdII-chlorido system and (at low ionic strengths) the CdII-sulfato system, the equilibrium reactions for the title systems are relatively poorly characterized. In weakly acidic fresh water systems (–log10 {[H+]/c°} < 6), in the absence of organic ligands (e.g., humic substances), CdII speciation is dominated by Cd2+(aq), with CdSO4(aq) as a minor species. In this respect, CdII is similar to CuII [2007PBa] and PbII [2009PBa]. However, in weakly alkaline fresh water solutions, 7.5 < –log10 {[H+]/c°} < 8.6, the speciation of CdII is still dominated by Cd2+(aq), whereas for CuII [2007PBa] and PbII [2009PBa] the carbonato- species MCO3(aq) dominates. In weakly acidic saline systems (–log10 {[H+]/cϒ} < 6; –log10 {[Cl–]/c°} < 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 CuII and PbII. However, in weakly alkaline saline solutions, including seawater, the chlorido- complexes still dominate the speciation of CdII because of the relatively low stability of CdCO3(aq). In contrast, the speciation of CuII [2007PBa] and PbII [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.
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