Adsorption of Rare-earth Metals on to Biochars from Posidonia oceanica

Rare earth metals belong to the list of criticai raw materials, i.e. thè list of materials whose recovery is considered strategie from thè European Community.1 Adsorption can be a valid recovery technique, mainly if thè adsorbents derive from raw materials.2,3 Here we report a study on thè adsorption capacity toward rare earth cations of three biochars obtained from thè pyrolysis of dead Posidonia oceanica, a marine plant that causes accumulations on thè cost, which are often treated as waste. In particular, thè adsorption of lanthanum, neodymium and dysprosium ions in aqueous solution on to biochar from Posidonia oceanica as it is (BC), and chemically activated by acid (BCA) and basic (BCB) treatments was studied at pH=5 and 25 °C. Chemical and morphological characterization of adsorbents was carried out by SEM-EDX, FT-IR, elemental analysis and nitrogen adsorption/desorption techniques. Thè results obtained from adsorption experiments show that Langmuir equation was thè best fitting isotherm model for BCA and BCB while for BC thè adsorption of rare-earth metals is poor. In terms of maximum adsorption capacity, thè best performing material was thè BCA. Thè kinetic data obtained from thè adsorption study of thè three metals on thè BCA confirm that thè equilibrium conditions are essentially reached within 24h. Recycling experiments conducted using a HNO3 (or EDTA) 0.1 M solution showed that, for each cycle, thè desorption of three rare earth cations is almost complete, instead thè adsorption decrease after thè first adsorption/desorption cycle. References 1 European Commission, https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=C ELEX:52023PC0160 (accessed 8 November 2023), 2023 2Cataldo, S.; Muratore, N.; Giannici, F.; Bongiorno, D.; Chiodo, V.; Maisano, S.; Pettignano, A., Environ. Sci. Pollut. Res., 2022, 29, 90231. 3Cataldo, S.; Chiodo, V.; Crea, F.; Maisano, S.; Milea, D.; Pettignano, A., J. Mol. Liq., 2018, 271,481.