Abstract
Fulvic acid extracted from lake sediments was treated with Amberlite XAD-2 and XAD-8 resins. The metal complexing ability of the fulvic acid was measured at pH 6.0 with a Cu2+ titration method, in which free Cu2+ was determined with an ion selective electrode. A two binding site model, in which there are two kinds of the molecules having strong and weak complexing ability and they complex with metal ion at the ratio of 1 : 1, was employed for the determination of the stability constant and complexing capacity of the fulvic acid, because the hyperbolic approxmation could apply to the Scatchard plot of the found values.
The stability constants of the fulvic acids having strong complexing ability and weak complexing ability were in the range of 6.33-7.12 and 4.35-4.66, respectively. Both colorless fractions of the fulvic acid which were not adsorbed on XAD-2 and XAD-8 resins had such a high complexing ability as 44 and 32 μmol·g-1, respectively.
On the other hand, both colored fractions of the fulvic acid which were adsobed on the resins had only little complexing capacity.
