Bergamot Pomace as a Biosorbent for Rare Earths: Outcomes of the Wastezilla Project

This study summarizes the main outcomes of the two-year Wastezilla project, focused on the recovery of Rare Earth Elements (REEs) from aqueous systems using waste biomasses from the agri-food industry. In particular, bergamot (BP), olive (OP), and grape (GP) pomaces, as well as biochar derived from Posidonia oceanica residues (CP), were investigated as low-cost and sustainable biosorbents for Nd and Dy (and, for comparison, 3+ 3+ La ) under controlled conditions. Preliminarily, a comprehensive characterization of the 3+ materials by Attenuated Total Reflectance Fourier Transform Infrared spectroscopy (ATR FT- IR) and Scanning Electron Microscopy – Energy Dispersive X-Ray Spectroscopy (SEM-EDX) confirmed the presence of surface functional groups suitable for metal binding, and Ion Selective Electrode (ISE-H ) potentiometry helped us in establishing desirable experimental + conditions (pH ≈ 5) to study the sorption process [1]. Batch adsorption experiments showed that equilibrium is reached very quickly (~ 120 min) and that the sorption process is well described by a pseudo-second-order kinetic model and Langmuir isotherms. For the first time, isothermal titration calorimetry (ITC) was applied to directly determine the thermodynamic parameters of REE adsorption onto biomass [2]. Among the tested materials, water-pretreated bergamot pomace and H PO -activated biochar (ABCP) exhibited the 34 3+ 3+ 3+ highest adsorption capacities, with a general selectivity trend Dy > Nd > La , an average maximum sorption capacity (qmax) of 0.45 mmol·g , and good reusability over four -1 adsorption/desorption cycles [2, 3]. The performance of bergamot pomace was further tested in a scaled-up scenario under dynamic conditions using column experiments with synthetic acid mine drainage (AMD) containing REEs and interfering ions. The AMD contained 27 metal cations: 16 REEs (excluding Sc) and 11 interfering ions (Ca , Mg , Mn , Na , Zn , Co , Ni , Sr , Ge , 2+ 2+ 2+ + 2+ 2+ 2+ 2+ 2+ 3+ 2+ As , Se ). Breakthrough curves (C/C vs. pore volumes) revealed preferential retention of 0 24 lanthanides, while sequential desorption with H SO [4] enabled effective recovery and partial fractionation of light and heavy REEs with a concentration factor of ~ 3. In parallel, bergamot pomace was also valorized as a precursor for the synthesis of carbon quantum dots (CQDs), whose photoluminescence properties of CQDs were exploited for sensing applications. Particle size evaluation and surface group analysis of CQDs was done through Transmission Electron Microscopy (TEM) and ATR-FTIR spectroscopy [5]. The obtained CQDs showed efficient fluorescence quenching in the presence of selected metal ions, including Nd and Dy , allowing the evaluation of binding interactions via Stern– 3+ 3+ Volmer analysis. Finally, Life Cycle Assessment (LCA), Life Cycle Costing (LCC), and Techno- Economic Assessment (TEA) highlighted the environmental and economic sustainability of the proposed approach. Overall, the results demonstrate the strong potential of bergamot pomace as a multifunctional platform for REE recovery and sensing, supporting circular economy strategies for critical raw materials.