Biosorption of cesium and strontium from aqueous solution by Aspergillus flavus biomass

This study investigates the potential biosorption of Aspergillus flavus biomass for the removal of Cs⁺ and Sr²⁺ ions from aqueous solutions. The biosorbent was characterized using FTIR, SEM-EDS, BET surface area analysis, and thermal stability tests, revealing key functional groups (-OH, -COOH, -NH₂) and a surface area of 9.65 m²/g. Batch adsorption experiments demonstrated that pH significantly influenced uptake, with optimal removal at pH 5 for Sr²⁺ (~ 90%) and pH 8 for Cs⁺ (~ 27%). Kinetic studies followed the pseudo-second-order model (R² > 0.97), indicating chemisorption dominance. Equilibrium data fitted the Freundlich isotherm, suggesting multilayer adsorption, with maximum capacities (qₘₐₓ) of 211.1 mg⋅g^-1 (Sr²⁺) and 26.7 mg⋅g^-1 (Cs⁺). Thermodynamic analysis revealed endothermic (ΔH > 0), spontaneous (ΔG < 0), and entropy-driven (ΔS > 0) adsorption. Competitive ion studies showed Ca²⁺ strongly inhibited Sr²⁺ uptake, while Na⁺ reduced Cs⁺ adsorption. The biosorbent exhibited excellent reusability (3 cycles) with 0.1 M HNO₃ as the best eluent (81.2% Sr²⁺, 71.5% Cs⁺ recovery). The proposed mechanisms include ion exchange, surface complexation, and electrostatic interactions. These findings highlight A. flavus as a promising, low-cost biosorbent for nuclear wastewater treatment.