Determination of Stability Constants of U(VI)-Fe(lll)-Citrate Complexes

摘要

Ion-exchange experiments were performed to evaluate the formation of the uranium-citrate and uranium-iron-citrate complexes over a wide concentration range;i.e.,environmentally relevant concentrations(e.g.,10~(-6)M in metal and ligand)and concentrations useful for spectroscopic investigations(e.g.,10~(-4)M in metal and ligand).The stability of the well-known uranium-citrate complex was determined to validate the computational and experimental methods applied to the more complex system.Values of the conditional stability constants for these species were obtained using a chemical equilibrium model in FITEQL At a pH of 4.0,the stability constant for uranium-citrate complex(log beta_1,1)was determined to be 8.71(+-)0.6 at / = 0.Analysis of the results of ion-exchange experiments for the U-Fe-citric acid system indicates the formation of the 1:1:1 and 1:1:2 ternary species with stability constants(log beta)of 17.10(+-)0.41 and 20.47(+-)0.31,respectively,at I = 0.