Waste-derived biosorbents for REEcovery from aqueous systems

This study addresses the growing demand for Critical Raw Materials (CRMs) by investigating sustainable alternatives to primary extraction. At the same time, agro-industrial waste biomasses represent a significant environmental and economic burden. In this framework, bergamot pomace (BP) was valorised as a low-cost biosorbent for the recovery of Rare Earth Elements (REEs), contributing to circular economy strategies. The material, after water pre-treatment, was characterized using a multi-technique approach to elucidate its surface chemistry and adsorption behaviour. Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) was used to identify surface functional groups and to monitor spectral changes after metal uptake [1]. The pH of point zero charge (pHpzc) was determined to investigate the surface charge of the adsorbent and to identify the optimal operating pH for REE uptake. The adsorption ability of BP was tested using two synthetic REEs solutions. The first contained only REEs, and the second also included the typical interfering cations in Acid Mine Drainages (AMDs). Dynamic column tests allowed the construction of breakthrough curves and the evaluation of dynamic adsorption capacity, relative affinity, and mass transfer phenomena. The results showed a higher affinity toward light REEs, as indicated by delayed breakthrough times. Desorption in column was carried out using H₂SO₄ solutions at 0.05 and 0.10 mol dm⁻³, achieving continuous elution with concentration factors ≥ 2.5 [2]. The recovered eluates were further treated by selective precipitation using NaOH and Na₂CO₃ at 1.0 mol dm⁻³. Life Cycle Assessment (LCA) and Techno Economic Assessment (TEA) showed which are the most relevant protocol steps to be optimized for the scaling up from a lab scale to an industrial scenario [3]. The laboratory configuration is associated with higher costs and environmental impacts, whereas process optimization, mainly through improved drying and biosorbent regeneration, leads to a significant reduction in both. In the optimized scenario, the production cost decreases to 2.99 € kg⁻¹ together with a marked improvement in the environmental footprint, supporting the scalability of the process.