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.

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.

Fluorescence Analysis of Cu(II), Pb(II) and Hg(II) Ion Binding to Humic and Fulvic Acids

2016 ◽  
Vol 851 ◽  
pp. 135-140 ◽  
Author(s):  
Vojtěch Enev ◽  
Irena Türkeová ◽  
Jana Szewieczková ◽  
Leos Doskocil ◽  
Martina Klučáková
Keyword(s):  
Humic Substances ◽  
Stability Constants ◽  
Metal Ion ◽  
Fluorescence Analysis ◽  
Fulvic Acids ◽  
Ion Binding ◽  
Conditional Stability ◽  
Metal Ion Binding ◽  
The Stability ◽  
Conditional Stability Constants

Abstract. The aim of this work was to study molecular and quantitative aspects of metal ion binding to humic substances (HS). The object of our study was characterization of two standards of humic substances (Elliott Soil standard HA 1S102H and Elliott Soil standard FA 2S102F). All samples of IHSS standards HS were characterized by elemental analysis (EA), ultraviolet-visible spectroscopy (UV/Vis), Fourier transform infrared spectroscopy (FTIR) and steady-state fluorescence spectroscopy. Chemical parameters on the complexation of Cu (II), Pb(II) and Hg(II), including the conditional stability constants and the percentage of fluorophores participating in the complexation, were estimated by the modified Stern–Volmer equation. The stability constants (log Ka) of Me(II)–ESHS complexes range from 3.70 to 5.15 in the order: Hg–ESHA>Cu–ESHA>Pb–ESHA>Cu–ESFA>Pb–ESFA. With respect to the ESHA, ESFA, which showed the smallest contents of O-containing functional groups (e.g. hydroxyl, carbonyl, ester, especially carboxyl groups on the aromatic ring) and the lowest humification degree, the ESFA was characterized by much smaller stability constants. Our findings suggest that soil HS belongs to class of important organic ligands for complexation with heavy metal ions and may significantly affect the chemical forms, mobility, bioavailability and ecotoxicity of heavy metals in the soil environment.

Interaction of Fulvic Acids with Al(III) Studied by Self-Modeling Curve Resolution of Second-Derivative Synchronous Fluorescence Spectra

1996 ◽  
Vol 50 (4) ◽  
pp. 436-443 ◽  
Author(s):  
Joaquim C. G. Esteves Da Silva ◽  
Adélio A. S. C. Machado
Keyword(s):  
Fulvic Acids ◽  
Synchronous Fluorescence ◽  
Soil Horizon ◽  
Conditional Stability ◽  
Second Derivative ◽  
Conditional Stability Constant ◽  
Curve Resolution ◽  
Synchronous Fluorescence Spectra ◽  
Two Samples ◽  
Conditional Stability Constants

The interaction of Al(III) with two samples of fulvic acids (fua), extracted from materials present in a pinewood soil (fua2 from the upper soil horizon, or leaf litter, and fua3 from lower soil horizons), was followed by synchronous fluorescence (SyF) spectroscopy at pH 4. The variations observed in the inverted second-derivative spectral data were analyzed by SIMPLISMA, a self-modeling curve resolution technique. Three binding sites were detected for each fua sample, and their spectra and SyF intensity profiles were obtained. Conditional stability constants for coordination of one binding site of each fua and Al(III) were obtained (log values): fua2, 5.65(15); fua3, 4.64(2). The experimental and data analysis methodologies were validated by analysis of data obtained for salicylic acid under the same conditions. The log value found for its conditional stability constant for Al(III) coordination at pH 4 was 4.34(15).

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