Spectroscopic Studies on the Binding of Uranium by Brown Coal

Abstract

Brown coal removes uranium from sea water where it is present mainly as [UO₂(CO₃)₃]⁴⁻. The adsorption and binding of uranium is studied by infrared spectroscopy. The spectra of the coal-uranium adducts still exhibit the asymmetric stretching vibration of the uranyl ion, but no CO₃²⁻ frequencies, suggesting that uranium is retained as UO₂²⁺. The coal humic acids are shown to be responsible for the decomposition of the carbonato complex. The subsequent uptake of uranium is not a pure cation exchange process since the shift of the asymmetric uranyl stretching frequency from 950 cm⁻¹ (hydrated UO₂²⁺) to 890 cm⁻¹ points to complexation of UO₂²⁺ by carboxylate groups which act as bidentate ligands.