The binding of Cd2+ to Suwannee River fulvic acid is studied using potentiometric methods and 113Cd NMR spectroscopy. The potentiometric results indicate 6.4 and 1.2 mequiv/g carboxylic and phenolic acid groups for the Suwannee River fulvic acid standard. At pH 6.4, the fraction of of the carboxylic acid groups that are deprotonated is 0.89. The observed 113Cd NMR chemical shift changes with constant Cd2+ concentration and varying fulvic acid concentration at pH 6.4 are consistent with the fast exchange model. Analysis of the 113Cd NMR chemical shift data using a Scatchard plot yields a conditional binding constant of 6.7 x 102 mL/mg. A number- average apparent molecular weight of 800 g/mol, gives a value of 0.9 for the fraction of the fulvic acid carboxylate sites that are bound to cadmium and a cadmium-fulvic acid complex formation constant of 5.4 x 102 M-1.
ASJC Scopus subject areas
- Environmental Chemistry