Determination of stability constants for rare earth elements and fulvic acids extracted from different soils

Fulvic acids (FAs) were extracted by alkali extraction from different soil samples in China, then purified using resins and characterized by Fourier t ransform infrared spectroscopy. The complexing ability of FAs was investiga ted by measuring the stability constants of rare earth elements (REEs) (La3 +, Ce3+, Sm3+, Gd3+, Y3+) With FAs by the ion exchange technique. The resul ts indicated that maximum binding ability for Y3+ (4.41 similar to 4.44) wa s higher than other REEs (La3+, Ce3+, Sm3+, Gd3+) (0.72 similar to 1.03). T here were two types of binding sites in the functional groups of fulvic aci ds. The complexing reaction followed two steps. The stability constants (K- 1 and K-2) of REEs with FAs were calculated from experimental data by divis ion of Scatchard plots into two straight-line segments. Y3+ (log K-1 = 5.72 +/- 0.05, log K-2 = 4.83 +/- 0.01) also has higher stability constants tha n the other four REEs (log K-1 = 4.37 +/- 0.16, log K-2 = 3.62 +/- 0.28). ( C) 2001 Elsevier Science B.V. All rights reserved.