Biosorption of uranyl ion from radioactive solution

U(VI) biosorption by six natural materials: three types of peats, Polytrichium moss, Eichhórnia crássipes water plant and Cladonia stellaris lichen was investigated. Natural sorbents were selected, as it is available, cheap and accessible materials. The effects of initial concentration of UO2^2- in the model radioactive solution and pH on the sorption uranyl ions were assessed. Adsorption isotherms and constants for given adsorbates and adsorbents were determined. Equilibrium is well described by Freundlich equation with the maximum biosorption capacity for Polytrichium moss as 70 mg/g after its interaction with UO₂(NO3)₂ solution (uranium initial concentration 959 mg/L, pH 4.4) during 24 hours. Our results reveal that peat is an efficient adsorbent for uranium that could be leached out from nuclear waste or U-containing rocks. One g/L of peat proved to be sufficient amount to remove contamination concentration of 0.3 mg/L U in contact time of 24 hours. IR spectroscopy allowed us to conclude that several functional groups in the organic compounds of examined sorbents participate in binding of the uranyl-ion: -CH, -COO, -COOH, -C=O. Therefore, the uranyl-ion bind with organic compounds of the peat and moss samples mainly due to the interaction of carboxyl group with uranyl-ions. The increased sorption in alkaline conditions and pH values decreased after experiments confirm the chemical sorption. However, the Freundlich adsorption isotherms and SEM mapping of the U species indicate surface adsorption also.