Competitive sorption of cesium and other microelements onto iron(III) hexacyanoferrate(II) in the presence of humic acids

Abstract

Experiments show that particles of iron(III) hexacyanoferrate(II) (Berlin Blue, FCFe), in contrast to those of oxyhydrates, and humic acids (HAs) in aqueous solutions have surface charges (ζ-potential) of the same sign. Therefore, contact coagulation and coarsening of FCFe particles in HA solutions are impossible (in contrast, e.g., to dicalcium silicate). HA molecules are capable of dimerization; therefore, the microelements (Cs, Sr, Co, Mn, Fe, Zr, Th, U) in humate solutions form complexes with HA monomer and dimers. It is demonstrated by the example of Cs(I) sorption from humate solutions that the monomeric and dimeric complexes of microelements exhibit different sorption affinity (Kd) for FCFe. Complexes of microelements with HA are kinetically inert and interact with the FCFe sorbent independently of each other. Therefore, it is possible to estimate separately the contribution of each form to the total sorption of the microelement. Except Cs(I), Ce(III), and Th(IV), the microelements under consideration in HA solutions have Kd by orders of magnitude higher than in HA-free solutions. Thus, the FCFe-HA system is capable of binding microelements in the form of humate complexes and of fixing these complexes on the FCFe surface. This phenomenon can be used for efficient decontamination of materials from artificial radionuclides.