Characterization of trace metal species and measurement of trace metal stability constants by electrochemical techniques

Ernst, R; Allen, Herbert E.; Mancy, K. H.

doi:10.1016/0043-1354(75)90125-6

Cited by 104 publications

(30 citation statements)

References 19 publications

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“…PbCO 3 (aq) and 6.1 and 5.7 for CuCO 3 (aq) [75EAa]. The absence of corrections for complexation of Pb 2+ and Cu 2+ by NO 3 -creates some ambiguity in both comparisons.…”

Section: Formation Of Pbco 3 (Aq)mentioning

confidence: 99%

Chemical speciation of environmentally significant metals with inorganic ligands. Part 3: The Pb2+ + OH–, Cl–, CO32–, SO42–, and PO43– systems (IUPAC Technical Report)

Powell

Brown

Byrne

et al. 2009

Pure and Applied Chemistry

141

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Complex formation between Pb II and the common environmental inorganic ligands, Cl -, OH -, CO 3 2-, SO 4 2-, and PO 4 3-, can be significant in natural waters with low concentrations of organic matter. Numerical modeling of the speciation of Pb II 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 log 10 β p,q,r°v alid at I m = 0 mol kg -1 and 25 °C (298.15 K), along with the equations and empirical coefficients required to calculate log 10 β p,q,r values at higher ionic strengths using the Brønsted-Guggenheim-Scatchard specific ion interaction theory (SIT). Some values for reaction enthalpies, Δ r H, are also reported.In weakly acidic fresh water systems (-log 10 {[H + ]/c°} < 6), the speciation of Pb II is similar to that of Cu II . In the absence of organic ligands, Pb II speciation is dominated by Pb 2+ (aq), with PbSO 4 (aq) as a minor species. In weakly alkaline solutions, 8.0 < -log 10 {[H + ]/c°} < 9.0, the speciation is dominated by the carbonato species PbCO 3 (aq) and Pb(CO 3 ) 2 2-. In weakly acidic saline systems (-log 10 {[H + ]/c°} < 6), the speciation is dominated by PbCl n (2-n)+ complexes, (n = 0-3), with Pb 2+ (aq) as a minor species. In this medium (and in seawater), the speciation contrasts with that of Cu II because of the higher stability of the Pb 2+ -chlorido-complexes. In seawater at -log 10 {[H + ]/c°} = 8.2, the calculated speciation is less well defined, although it is clearly dominated by the uncharged species PbCO 3 (aq) (41 % of [Pb] T ) with a significant contribution (16 %) from Pb(CO 3 )Cl -and minor contributions (5-10 %) from PbCl n (2-n)+ , (n = 0-3) and Pb(CO 3 ) 2 2-. The uncertainty in calculations of Pb II speciation in seawater arises from (a) the large uncertainty in the stability constant for the apparently dominant species PbCO 3 (aq), (b) the reliance on statistical predictions for stability constants of the ternary species Pb(CO 3 )Cl -and Pb(CO 3 )OH -, and (c) the uncertainty in the stability constant for PbCl 4 2-, the available value being considered

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“…PbCO 3 (aq) and 6.1 and 5.7 for CuCO 3 (aq) [75EAa]. The absence of corrections for complexation of Pb 2+ and Cu 2+ by NO 3 -creates some ambiguity in both comparisons.…”

Section: Formation Of Pbco 3 (Aq)mentioning

confidence: 99%

Chemical speciation of environmentally significant metals with inorganic ligands. Part 3: The Pb2+ + OH–, Cl–, CO32–, SO42–, and PO43– systems (IUPAC Technical Report)

Powell

Brown

Byrne

et al. 2009

Pure and Applied Chemistry

141

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“…A value of 0.6 has been observed in other studies (6, lo), and a value of 1.0 would be expected if the mode of coordination by fulvic acid is similar to that exhibited by salicylic acid where one donor is a carboxyl oxygen and the other is a phenolic oxygen. It is presumed that the pK,'s of the phenolic oxygens will be greater than 8 and thus hydrogen ion dependence should approach unity. This interpretation assumes that the mode of complexation in each fulvic acid molecule is similar and thus can be quantitatively compared to precisely defined complexing agents.…”

Section: C6lmentioning

confidence: 99%

“…Anodic stripping voltammetry (5,6), differential pulse polarography (7,8), and ion selective electrodes (9, lo), have also been utilized to determine the degree of trace metal complexation in a variety of waters.…”

mentioning

confidence: 99%

Cadmium complexation by soil fulvic acid

Brady¹,

Pagenkopf²

1978

Can. J. Chem.

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A soil fulvic acid bas been characterized and the complexation stability constants with cadmium have been evaluated. The average gram formula weight of the fulvic acid is 2775. Three complexes of stoichiometry CdFA, Cd2FA, and Cd3FA have been observed. The respective conditional stability constants at pH 5.7 are 105.3, 109.8, and 1014.0; at pH 6.7 they are 105.6, 1010.6, and 1015.5; and at pH 7.7 they are 106.0, 1010.7, and 1015.4.

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“…There are several techniques for investigating the metal ion distribution in solution: anodic stripping voltammetry (ASV) (15)(16)(17), ion selective electrodes (18,19), and dialysis or ultrafiltration (20,21). Guy and Chakrabarti (22) have compared ASV and size separation procedures and concluded that, since the adsorption of organic substances onto the hanging mercury drop electrode makes the interpretation of stripping voltammograms difficult, the size separation procedures were more convenient.…”

Section: Introductionmentioning

confidence: 99%

Studies of metal–organic interactions in model systems pertaining to natural waters

Guy¹,

Chakrabarti²

1976

Can. J. Chem.

153

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Zn(I1) with humic and tannic acids were studied to evaluate the possibility of metal speciation using a combination of dialysis/atomic absorption spectroscopy, and the p H characteristics of the metal-organic species. The stability constants of metal-organic complexes were found to decrease in the order Pb(I1) > Cu(I1) > Cd(I1) > Zn(I1) and EDTA > humic acid > tannic acid. Scatchard plots for the metal -humic acid systems indicated two types of binding sites with a difference in stability constants of about 10. Ultrafiltration of metal -humic acid solutions indicated that the metal ions were concentrated in the large molecular size fractions ( > 3.1 nm). Separation by dialysis was used to investigate the release of metal from model sediment components by the organic acids (the metalorganic complexes were non-dialyzable). For release of copper from bentonite, it was found that the amount of copper released depended on both the concentration of ligand and the stability constant of metal complex, with the ratio of metal release to complexing sites decreasing in the order EDTA > humic acid > tannic acid. Release of metal from the solids decreased in the order: bentonite > Mn02 > humic acid. Release of metal from the hydrous oxides via a redox decomposition of the oxide by natural organics was investigated using pyrogallol, gallic, and tannic acids. At natural water p H levels (6-8), 20pg/ml solutions of the organic acids released 20 pmol manganese per 100 ml solutions whereas at p H 2, 60 pmol manganese were released. The pH behaviour of the organic acids has been explained in terms of formation of oxalic acid at p H < 5, which then reduces the hydrous oxide. Chem. 54, 2600Chem. 54, (1976. Faisant appel a une combinaison de spectroxopie atomique, de dialyse ainsi qu'aux caract6 ristiques de p H des esp6es organometalliques, on a 6tudie les interactions de Cu(II), de Pb(II), de Cd(I1) et de Zn(I1) avec les acides humique et tannique dans le but d'kvaluer la possibilitk de spkiation des metaux. On a trouvC que les constantes de stabilitk des complexes organom6talliques dkroissent dans I'ordre Pb(1I) > Cu(1l) > Cd(I1) > Zn(l1) et EDTA > acide humique > acide tannique. Les courbes de Scatchard pour les systtmes acide humique/metal indiquent qu'il y a deux types de sites de couplage et que la difference entre leurs constantes de stabilitk est d'environ 10. L'ultrafiltration de solutions de mCtal/acide humique indique que les ions metalliques sont concentres dans les fractions de grands poids molkulaires ( > 3.1 nm). On a utilisC la separation par dialyse pour examiner la liberation, par les acides organiques (les complexes organometalliques ne sont pas dialysables), des metaux attaches a des composants modkles de suiments. Pour la liberation du cuivre de la bentonite, on a trouvC que la quantitk de cuivre libere depend la fois de la concentration des ligands et de la constante de stabilite du complexe mCtallique avec un rapport de liberation du metal par rapport aux sites complexants qui diminue dans I'ordre EDTA > aci...

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Characterization of trace metal species and measurement of trace metal stability constants by electrochemical techniques

Cited by 104 publications

References 19 publications

Chemical speciation of environmentally significant metals with inorganic ligands. Part 3: The Pb2+ + OH–, Cl–, CO32–, SO42–, and PO43– systems (IUPAC Technical Report)

Chemical speciation of environmentally significant metals with inorganic ligands. Part 3: The Pb2+ + OH–, Cl–, CO32–, SO42–, and PO43– systems (IUPAC Technical Report)

Cadmium complexation by soil fulvic acid

Studies of metal–organic interactions in model systems pertaining to natural waters

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