Modeling Uranium-Proton Ion Exchange in Biosorption

Biosorption of uranium metal ions by a nonliving protonated Sargassum fluitans seaweed biomass was used to remove the heavy metal uranium from the aqueous solution. Uranium biosorption isotherms were established for solution pH values ranging from pH 2.5-4.0. Uranium biosorption uptake was accompanied by the release of protons from the biomass. The sorption isotherms were highly pH dependent, and the metal binding increased significantly with increasing pH values. Above pH 3.0, the maximum uranium uptakes exceeded the total biomass binding capacity as expressed in equivalents units. A mathematical model based on the ion exchange between protons in the biomass and hydrolyzed uranium ion species was developed. Given the total uranium concentration and pH value, the model can calculate the uranium and proton binding as well as the composition of uranium ionic groups in the solution and on the biosorbent. The model was capable of fitting and predicting biosorption isotherms for different pH values as well as the equilibrium uranium desorption concentrations.