EQUILIBRIUM DIALYSIS LIGAND-EXCHANGE - ADAPTATION OF THE METHOD FOR DETERMINATION OF CONDITIONAL STABILITY-CONSTANTS OF RADIONUCLIDE FULVIC-ACID COMPLEXES

The equilibrium dialysis-ligand exchange technique (EDLE) has been ada pted to measure conditional stability constants for the complexation o f metal ions with fulvic acid. Since fulvic acid permeates across the membrane during the experiment, the quantities involved have to be det ermined analytically and taken into account when calculating the condi tional stability constants. It is shown here that the larger diffusion rates of fulvic acid compared to those of humic acid do not lead to e nhanced errors in the results. Conditional stability constants (K-c(FA )) of Laurentian Soil fulvic acid are determined at various pH values and ionic strengths for the binding of Co2+ and UO22+. Over the whole pH range, at ionic strength of 0.2 M, log(K-c(FA)) averages half a log unit lower than at ionic strength of 0.02 M. A comparison with the co rresponding binding constants measured for Aldrich humic acid (K-c(HA) ) by the conventional EDLE technique shows that log(K-c(FA)) values di ffer by not more than one order of magnitude from log(K-c(HA)) values.