Removal of uranium(VI) from aqueous solution by Camellia oleifera shell-based activated carbon: adsorption equilibrium, kinetics, and thermodynamics.

Camellia oleifera shell-based activated carbon (COSAC) was prepared by HPO activation method and further used to remove U(VI) from the aqueous solution in a batch system. This research examined the influence of various factors affecting U(VI) removal, including contact time, pH, initial U(VI) concentration, and temperature. The results showed that the U(VI) adsorption capacity and removal efficiency reached 71.28 mg/g and 89.1% at the initial U(VI) concentration of 160 mg/L, temperature of 298 K, pH 5.5, contact time of 60 min, and COSAC dosage of 2.0 g/L. The pseudo-first-order, pseudo-second-order, and intraparticle diffusion equations were used to identify the optimum model that can describe the U(VI) adsorption kinetics. The pseudo-second-order kinetics model performed better in characterizing the adsorption system compared with the pseudo-first-order and intraparticle diffusion models. Isotherm data were also discussed with regard to the appropriacy of Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich models. The Langmuir model described the U(VI) adsorption process the best with a maximum adsorption capacity of 78.93 mg/g. Thermodynamic analysis (ΔG < 0, ΔH > 0, and ΔS > 0) indicated that the U(VI) adsorption process is endothermic and spontaneous. All the results imply that COSAC has a promising application in the removal or recovery of U(VI) from aqueous solutions.