Biochars of dead Posidonia oceanica leaves as adsorbents of rare-earth elements

Thè widespread use of Rare earth elements (REE) in cutting-edge technologies has led to a surge in their consumption and thè urgency of fmding sustainable solutions for their recovery.1 Thè European Community included REE in thè list of criticai raw materiate, i.e. thè list of materiate whose recovery is considered of strategie interest.2 Among thè different REE recovery methods, adsorption is one of thè most attracting, in partìcular when thè employed adsorbents come from waste platforms? This contribution presenta thè resulta achieved using three biochars coming from thè pyrolysis of dead Posidonia oceanica, a marine plant whose leaves accumulate in abundance on thè sicilian cost, as adsorbents of REE from aqueous solutions. To this end, thermodynamic and kinetic experiments were carried out to study thè recovery of La, Nd and Dy ions onto thè biochar of Posidonia oceanica as it was (BC) and after two types of chemical activations, i.e., an acid activation with phosphoric acid (BCA) and a basic activation with potassium hydroxide (BCB) in aqueous solution at pH = 5 and t = 25°C. Thè adsorption of REE ions onto BCA, thè best adsorbent among those investigated, was ateo studied, at thè sanie pH, in NaNCfc 0.1 mol L1 to evaluate thè effect of ionie strength. Single batch adsorption experiments were also carried out at pH = 3 and 6 to evaluate thè effect of pH. Chemical and moiphological characterization of adsorbente were carried out by SEM-EDX, FT-IR, dementai analysis, nitrogen adsorption/desorption and pH of point zero charge measurements. Thè REE adsorption were well described by Langmuir isotherm and, among thè adsorbents investigated, thè BCA showed thè highest qm value. Thè qm of BCA decreases with thè decreasing of pH and in presence of NaNO3. Thè adsorption equilibrium was reached within 8 hours and thè kinetic of adsorption was well described by thè doublé exponential equation. Recycling experiments were also carried out to test thè reusability of thè BCA. Acknowledgements We thank MUR: PNRR - Missione 4, Componente 2, Investimento 1.1 - Bando Prin 2022 - Decreto Direttoriale n. 104 del 02-02-2022. Project title: “Wastezilla: Recycled waste biomass for efficient recovery of criticai elements”. CUP: B53D23013740006 - project code: 2022HYH95P_003 References: [1] T.B. da Costa, M.G.C. da Silva, M.G.A. Vieira, J Rare Earths, 38(4), 339-355. [2] European Commission, https://www.consilium.europa.eu/it/infographics/critical-raw-materials/ (accessed 14 March 2024), 2024. [3] S. Cataldo, N. Muratore, F. Giannici, D. Bongiomo, V. Chiodo, S. Maisano, A. Pettìgnano, Environ. Sci. Pollut. Res., 2022,29, 90231-90247.