Wheat bran as natural reagent for bio-recovery of Eu(III) following Box-Behnken optimization and the thermodynamics study

• Agro -waste Wheat bran exhibits good adsorption percentage for Eu(III). • Utilising the Box–Behnken design of response surface methodology , the condition of Eu(III) adsorption was established. • pH 2.5, temperature 313 K, adsorbent dosage of 20 mg, and an initial metal ion concentration of 1.06 mg/L was most suitable. • Dubinin–Radushkevich isotherm, yielded mean free energy (E) values ranging from 11.952 to 15.811 kJ/mol, indicating chemisorption . • ΔG = –12.19 kJ/mol, ΔH = 36.06 kJ/mol, and ΔS = 0.167 kJ/mol/K at 293 K, indicated that the adsorption process is spontaneous and endothermic. The present investigation provides a cost effective and eco-friendly method to recover Eu(III) from aqueous solution using an easily available agro-waste wheat bran as a bio-sorbent. The biosorbent was characterised using FTIR and SEM followed by elemental detection. Utilizing Box-Behnken design of response surface methodology, the optimum conditions for adsorption were found with pH 2.5, temperature 313 K, adsorbent dosage of 20 mg, and an initial metal ion concentration of 1.06 mg/L. Various adsorption isotherms were applied to determine the nature of the adsorption process. The best-fitting model, the Dubinin–Radushkevich isotherm, yielded mean free energy (E) values ranging from 11.952 to 15.811 kJ/mol, indicating chemisorption . Adsorption kinetic models have been implemented to further investigate the mechanism of adsorption. The obtained data fit well in the pseudo second order kinetic model and Bangham model with R 2 values of 0.9904 and 0.9545 respectively. The adsorption capacity obtained by pseudo second order kinetics is 116.7 µg/g. Adsorption studies were also established in presence of different metal ions such as Fe(III), Ni(II), Cu(II), Zn(II). 73 % of europium was recovered by desorption using 3 M of HCl after three cycles. The thermodynamic parameters like ΔG = –12.19 kJ/mol, ΔH = 36.06 kJ/mol, and ΔS = 0.167 kJ/mol/K at 293 K, indicated that the adsorption process is spontaneous and endothermic. Overall, this study demonstrates that wheat bran has significant potential as an agro-waste with sustainable biosorbent property for the recovery of Eu(III) from industrial wastewater.