Lead(II)-fulvic acid complexes. Conditional stability constants, solubility, and implications for lead(II) mobility

1980 ◽  
Vol 14 (7) ◽  
pp. 877-880 ◽  
Author(s):  
Robert A. Saar ◽  
James H. Weber
Keyword(s):  
Fulvic Acid ◽  
Stability Constants ◽  
Conditional Stability ◽  
Conditional Stability Constants

Cadmium complexation by soil fulvic acid

1978 ◽  
Vol 56 (17) ◽  
pp. 2331-2336 ◽  
Author(s):  
Bill Brady ◽  
Gordon K. Pagenkopf
Keyword(s):  
Fulvic Acid ◽  
Stability Constants ◽  
Conditional Stability ◽  
Cadmium Complexation ◽  
Conditional Stability Constants

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.

Complexation of cadmium(II) with water- and soil-derived fulvic acids: effect of pH and fulvic acid concentration

1979 ◽  
Vol 57 (11) ◽  
pp. 1263-1268 ◽  
Author(s):  
Robert A. Saar ◽  
James H. Weber
Keyword(s):  
Stability Constant ◽  
Fulvic Acid ◽  
Stability Constants ◽  
Acid Concentration ◽  
Conformational Changes ◽  
Fulvic Acids ◽  
Conditional Stability ◽  
Conditional Stability Constant ◽  
Weak Binding ◽  
Conditional Stability Constants

We studied the conditional stability constants of cadmium(II) bound to fulvic acid derived from water and soil, and found that (1) stability constants increased with increasing pH, and (2) stability constants decreased as we increased the fulvic acid concentration toward 70 mg/L. The second effect does not occur for the copper(II)–fulvate system. Conformational changes that occur when a fulvic acid solution becomes more concentrated apparently weaken sites that are otherwise more accessible to weak-binding cadmium. From pH 4 to 8, the overall conditional stability constant increases from 1.4 to 12 × 103 for water-derived fulvic acid and from 1.7 to 43 × 103 for soil-derived fulvic acid. Increases in fulvic acid concentration from 20 mg/L to 70 mg/L halve the conditional stability constant at a given pH.

Effect of pH, humus concentration and molecular weight on conditional stability constants of cadmium

1988 ◽  
Vol 22 (11) ◽  
pp. 1381-1388 ◽  
Author(s):  
Jan John ◽  
Brit Salbu ◽  
Egil T. Gjessing ◽  
Helge E. Bjørnstad
Keyword(s):  
Molecular Weight ◽  
Stability Constants ◽  
Conditional Stability ◽  
Effect Of Ph ◽  
Conditional Stability Constants

Comparison of Mn2+, Co2+, and Cu2+ binding to fulvic acid as measured by fluorescence quenching

1983 ◽  
Vol 61 (7) ◽  
pp. 1505-1509 ◽  
Author(s):  
David K. Ryan ◽  
Carl P. Thompson ◽  
James H. Weber
Keyword(s):  
Fluorescence Quenching ◽  
Fulvic Acid ◽  
Binding Capacity ◽  
Outer Sphere ◽  
Conditional Stability ◽  
Complexing Capacity ◽  
Fluorescence Quenching Titration ◽  
Conditional Stability Constants ◽  
Slight Advantage ◽  
Binding Curves

The binding of Cu2+ to soil-derived fulvic acid (SFA) measured by fluorescence quenching titration is much stronger than Co2+ and Mn2+ which are similar. The conditional stability constants from curve fitting at pH 6 are 1.1 × 105 for Cu2+, 5.1 × 103 for Co2+, and 4.2 × 103 for Mn2+. The slight advantage in strength for Co2+ over Mn2+ is also demonstrated by the binding curves at pH 6 and 7. These two metal ions not only tend to bind more weakly but also bind to fewer sites, giving complexing capacity values of about 1.5 × 10−6 M compared to 2.0 × 10−5 for Cu2+ at pH 6. This lower binding capacity may be due to outer sphere complexation that does not allow access to some sites complexed by inner sphere binding Cu2+. Scattering experiments demonstrate that Cu2+ is more effective at precipitating and aggregating SFA than Co2+ and Mn2+. Cu2+ probably neutralizes the negative charges on SFA molecules allowing larger hydrophobic aggregates to form and precipitate.

The Ion-exchange Behaviour of Beryllium Salicylate Complexes

1963 ◽  
Vol 16 (3) ◽  
pp. 376
Author(s):  
HJ de Bruin ◽  
JJ Fardy ◽  
RB Temple
Keyword(s):  
Ionic Strength ◽  
Ion Exchange ◽  
Stability Constants ◽  
Conditional Stability ◽  
Conditional Stability Constants ◽  
Exchange Behaviour ◽  
Chelate Rings

The beryllium/salicylate system has been re-examined by ion-exchange procedures. The results appear to confirm the existence of a neutral 1 : 1 and an anionic 1 : 2 complex, in both of which the salicylate radicals form chelate rings. Conditional stability constants have been measured at 25�C at an ionic strength of 0.15, the values obtained being ������������� β1 = 4.97 x 1012, and β2 = 2.63 x 1022.

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