Sustainable recovery of rare earth elements from aqueous media using fruit pomaces: adsorption performance, thermodynamics, and environmental assessment

The valorization of waste biomasses for recovering Critical Raw Materials (CRMs), particularly Rare Earth Elements (REEs), is a promising approach to enhance sustainability and resource efficiency. This study investigates the adsorption performance of bergamot, grape, and olive pomaces toward Nd3+ and Dy3+ ions under varying pH conditions, both in the absence of an ionic medium and in 0.10 mol/dm3 NaNO3(aq), following different biomass pretreatment protocols. Comparative tests with La3+ enabled evaluation of light (Nd3+, La3+) vs. heavy (Dy3+) lanthanide ion behavior. Biomass characterization was performed using Attenuated Total Reflectance Fourier Transform Infrared (ATR FT-IR) spectroscopy and Scanning Electron Microscopy – Energy-Dispersive X-ray (SEM-EDX) analysis to assess changes in surface chemistry and morphology after adsorption. Kinetic and isotherm analyses showed pseudo-second-order kinetics and Langmuir behavior, respectively. The highest capacity was observed for water-pretreated bergamot pomace at 30 °C, pH 5.0, without ionic medium, and measured adsorption efficiency followed the trend: Dy3+ (0.45 mmol/g) > Nd3+ (0.38 mmol/g) > La3+ (0.35 mmol/g). The materials exhibited good reusability across adsorption/desorption cycles, supporting their potential as sustainable biosorbents. For the first time, direct isothermal titration calorimetry (ITC) was used to determine adsorption thermodynamics. Life Cycle Assessment (LCA) and Techno-Economic Assessment (TEA) further evaluated the environmental and economic feasibility of bergamot pomace under different processing scenarios.