EXAFS investigation of the interaction of hafnium and thorium with humic acid and Bio-Rex70

The interaction of hafnium(TV) and thorium(IV) with humic acid, HA, is studied using EXAFS and compared to the interaction of these metal ions with carboxylate groups of the cation exchanger Bio-Rex70. Fourier-filtered Hf and Th L3 edge transmission EXAFS for the first oxygen shell is analyzed. For both Hf(IV)HA and Hf(IV)-Bio-Rex70, in wet paste and air-dried forms, 6-7 oxygen atoms at R=2.14 Angstrom are found. Th(IV)-HA also exhibits coordination similar to Th(IV)-Bio-Rex70. These observations support conclusions from previous studies on U(VI)-HA that metal cations are sorbed primarily onto HA carboxylate groups; other HA functional groups play a less significant role. (au)