Sequestering of uranium (VI) onto eucalyptus bark: kinetic, equilibrium and thermodynamic studies

The current study indicates the sequestering of uranium (VI) onto eucalyptus bark. The batch-scale removal of uranium (VI) onto eucalyptus bark has been investigated with various parameters, such as contact times, pH, biosorbent dose, temperatures and initial uranium (VI) concentrations. Value of R2 and six non-linear regression error functions, namely hybrid fractional error function, Marquardt’s percent standard deviation, average relative error, sum of the errors squared, sum of the absolute errors and Chi-square test (χ2), are considered as tools to predict the most optimum kinetic and isothermal models. The experimental results fitted well to the pseudo-second-order kinetic and Langmuir isothermal models. Maximum sorption capacity (48.99 mg/g) of eucalyptus bark was observed at optimum conditions (pH 6, contact time of 80 min, 0.05-g/L biosorbent dose, 35°C temperatures and initial uranium (VI) concentration of 90 mg/L). The thermodynamics of uranium (VI) ions sorption onto eucalyptus bark indicates the spontaneous and exothermic nature of the process. The competitive biosorption of Zn(II), Cd(II), Cr(III) and Pb(II) with uranium was studied and results depicted that Cr3+ had the most inhibitory effect, while Pb2+ had the least inhibitory effect on uranium biosorption. Decrease in peak sharpness in the loaded sample compared to native supports the involvement of functional groups in the sorption process. The results of the study prove that eucalyptus bark is a very useful and economical biosorbent for the removal of uranium (VI) from aqueous solutions.