Studies on salophen anchored micro/meso porous activated carbon fibres for the removal and recovery of uranium

Abstract

Stringent environmental regulations emphasize the removal of uranium from aqueous systems. Activated carbon fibers (ACF) were functionalized by oxidation (ACF-OX) and salophen ligand (ACF-Sal) and evaluated for the removal of uranium. The prepared sorbents were characterized by various techniques such as scanning electron microscopy (SEM), energy dispersive X-ray (EDAX), Fourier transform infrared (FTIR) spectroscopy, Brunauer–Emmett–Teller (BET) surface area analyzer and X-ray photoelectron spectroscopy (XPS). The anchoring of salophen ligand onto ACF surface was evident from the FTIR and XPS studies. The adsorption properties of UO₂²⁺ as a function of pH and contact time were characterized by inductively coupled mass spectrometry (ICPMS). The adsorption kinetics fitted the pseudo second order kinetics and equilibrium was reached within 180 minutes. The experimental data were modelled with Langmuir and Freundlich isotherms and various isotherm parameters were evaluated. The maximum adsorption capacities of U(VI) at pH 6 for ACF, ACF-OX and ACF-Sal were found to be 22.2, 50.0 and 142.8 mg g⁻¹, respectively. Thermodynamic studies revealed the spontaneity of the reaction and influence of other cations and anions on the sorption behaviour of uranium has been studied. Studies have been conducted to demonstrate the recyclability of the sorbent for five consecutive sorption desorption cycles. Using FTIR and XPS studies, a suitable mechanism for uranium sorption has also been postulated.