Study on Sorption Characteristics of Uranium onto Biochar Derived from Eucalyptus Wood

Abstract

In this study, the sorption characteristics of U(VI) onto eucalyptus biochar as a function of various operating parameters such as solution pH, initial metal ion concentration, contact time and ionic strength of the medium are reported. Biochar was characterised using various techniques such as CHNS element analysis, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). SEM analysis showed the presence of micro- and macropores in the sorbent, and FTIR spectra confirmed the presence of functional groups like carboxylic (−COOH), hydroxyls(−OH), carbonyls(–C=O), etc. Maximum sorption of about 95% is found to occur in the pH range of 5 to 6. U(VI) sorption onto biochar reached equilibrium within 20 min at pH 5.5. The kinetic data were analysed using both pseudo-first-order and pseudo-second-order kinetic models, and the latter is found to be more appropriate to explain the observed kinetics. The equilibrium data were correlated with Langmuir and Freundlich models, and the maximum monolayer adsorption capacity obtained from the Langmuir model was 27.2 mg/g at 293 K. From EDS, FTIR and XPS measurements, it is found that the sorption process involves chemical interaction between the U(VI) and the surface functional groups on the adsorbent. Efficient removal of low level of uranium from ammonium diuranate supernatant demonstrates its utility as sorbent for waste water treatment.