Kinetics and Thermodynamics of Uranium (VI) Adsorption onto Humic Acid Derived from Leonardite
ERDC Vicksburg United States
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Humic acid HA is well known as an inexpensive and effective adsorbent for heavy metal ions. However, the thermodynamics of uranium U adsorption onto HA is not fully understood. This study aimed to understand the kinetics and isotherms of UVI adsorption onto HA under different temperatures from acidic water. A leonardite-derived HA was characterized for its ash content, elemental compositions, and acidic functional groups, and used for the removal of U VI from acidic aqueous solutions via batch experiments at initial concentrations of 0100 mgL-1 at 298, 308 and 318 K. ICP-MS was used to determine the UVI concentrations in solutions before and after reacting with the HA. The rate and capacity of HA adsorbing UVI increased with the temperature. Adsorption kinetic data was best fitted to the pseudo second-order model. This, together with FTIR spectra, indicated a chemisorption of UVI by HA. Equilibrium adsorption data was best fitted to the Langmuir and Temkin models. Thermodynamic parameters such as equilibrium constant K0, standard Gibbs free energy G0, standard enthalpy change H0, and standard entropy change S0, indicated that UVI adsorption onto HA was endothermic and spontaneous. The co-existence of cations Cu2, Co2, Cd2 and Pb2 and anions HPO42- and SO4 2- reduced UVI adsorption. The high propensity and capacity of leonardite-derived HA adsorbing UVI suggests that it has the potential for cost-effective removal of UVI from acidic contaminated waters.
- Water Pollution and Control
- Physical Chemistry