Study of the removal of Th(IV) and U(VI) from aqueous solutions using lemon charcoal

This study evaluated the adsorption potential of lemon-derived charcoal for removing Th(IV) and U(VI) ions from aqueous solutions. The adsorbent was characterized using Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), powder X-ray diffraction (P-XRD), scanning electron microscopy (SEM), and Brunauer–Emmett–Teller (BET) surface area analysis, revealing a specific surface area of 123.65 m 2 /g and a pore volume of 0.468 cm 3 /g. Additional physicochemical properties, including point of zero charge, bulk density, porosity, and cation exchange capacity, were also determined. Optimal adsorption occurred at an adsorbent dose of 0.03 g, pH 4.0, and contact times of 20 mins for Th(IV) and 60 mins for U(VI). Kinetic studies indicated that adsorption followed the pseudo-second-order model for both ions. The equilibrium data were fitted to four isotherm models—Freundlich, Langmuir, Dubinin–Radushkevich, and Temkin—yielding maximum adsorption capacities (q m ) of 75.15 mg/g for Th(IV) at 25.0°C and 44.26 mg/g for U(VI). Thermodynamic analysis (ΔH°, ΔS°, ΔG°) confirmed that the adsorption process was spontaneous and exothermic.