Radionuclide sorption onto low-cost mineral adsorbent

This paper investigates the underlying mechanism of the removal of hexavalent uranium radionuclides from aqueous solution via a low-cost mineral adsorbent. Batch adsorption studies were performed for the concentration range of 50-4000 mg/L. The effects of contact times in the range of 10-3600 min (60 h), solution pHs in the range of 1-11, initial concentrations of metal ions in the range of 50-4000 mg/L, and interfering cations (such as Pb2+, Cu2+, Fe2+, Cd2+, Ni2+, Th4+, Ca2+, Na+, and K+) and interfering anions ( such as SO4-, CO3-, NO3-, and Cl-) were studied by equilibrating different concentrations of uranium solutions. Pseudo-first-order and pseudo-second-order rate expressions have been used to test the experimental data. The rate constants of adsorption for both the kinetic models have been calculated. The pseudo-second-order rate reaction provides the best correlation of the data. The values of adsorption data were fitted to Freundlich, Langmuir, and Dubinin-Radushkorich (D-R) adsorption isotherms. The mean energy of adsorption was calculated to be 10.10 kJ/mol from the D-R adsorption isotherm. The probable mechanism of radionuclide removal was its dissolution, followed by subsequent precipitation. X-ray diffractograms of the radionuclidesorbed mineral adsorbent indicates the precipitation of new compound at a higher radionuclide concentration (> 100 mg/L).