Sustainable and efficient sorption of uranium (VI) from aqueous solutions using alkali-activated cotton stalk with characterization, mechanistic insights and reusability

Abstract Eco-friendly alkali-activated cotton stalk was utilised for uranium (VI) sorption from aqueous solutions. The structure and morphology of the sorbent were characterised and elucidated by Fourier transform infrared (FTIR) spectroscopy, energy-dispersive X-ray (EDX) spectroscopy, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The effects of various parameters, including pH, contact time, initial uranium concentration, and temperature, upon uranium sorption efficiency were investigated. The maximum sorption efficiency attained was 78.42% using cotton stalk activated with 0.5 M NaOH compared to with 45.7% for inactivated cotton stalk under the optimum conditions of an initial pH 4.0, sorbent dosage of 0.5 g L 1- , a temperature of 298 K, and an equilibrium time of 60 min. Isotherm studies demonstrated that the process conformed to the Langmuir sorption model, exhibiting a maximum capacity of 156.84 mg g -1 , and adhered to a pseudo-second-order kinetic model. The thermodynamic parameters (ΔGº, ΔHº, and ΔSº) indicated that the process was feasible, spontaneous, and exothermic. Uranium was successfully desorbed from the loaded sorbent using 0.01 M EDTA, and the sorbent was recycled with minimal decrease in sorption and desorption efficiencies for at least five consecutive cycles. The activated cotton stalk (ACS) shows promising potential for U(VI) removal as well as good durability, reproducibility, and long-term stability. Finally, its applicability was further demonstrated using an Egyptian monazite ore leachate.