Sorption of uranium from carbonate-containing solutions by inorganic sorbents. X. Mechanism of uranium sorption by fibers packed with finely divided sorbents

We studied uranium sorption from pH 7.85 ± 0.05 seawater, containing standard amounts of uranium, onto polyacrylonitrile fibers to which was added during their preparation 50-80% of titanium-containing Termoksid-5 sorbent ground to 1-3 μm. Sorption isotherms obtained at various temperatures between 20 and 65 degree C and at various degrees of sorbent packing were linear in coordinates of 1n kd vs. 1n cs,∞. Fibers 50% packed were found to have the greatest sorptive capacity. Semiempirical equations were given for calculating sorbent distribution coefficients and capacities for uranium over a wide range of temperature, sorbent content in the fiber, and equilibrium uranium concentrations in carbonate-containing solutions. A comparison of equation parameters obtained by extrapolating to 100% sorbent fillage in the fibers with like equations for the sorbent in a free granulated state showed similar process thermodynamics for both types of solvent. We proposed a hydrolytic sorption mechanism involving the formation of a hydrated uranium oxide film on the sorbent surface and its pores as a results of the solution reacting with the sorbent and thereby shifting the solution pH at the surface interfaces