Thermodynamic and kinetic studies on REE ions recovery onto biochar of dead Posidonia oceanica leaves

Abstract

The widespread use of rare earth elements (REE) in cutting-edge technologies has led to an increase in their consumption and the urgency of finding sustainable solutions for their recovery.The European Community included REE in the list of critical raw materials, i.e. the list of materials whose recovery is of strategic interest. Adsorption by using materials derived from biomass is considered one of the most promising recovery techniques being cost-effective and in line with the principles of environmental sustainability and of circular economy. In the present contribution are reported the results of the adsorption study of three REE cations, namely La3+, Nd3+ and Dy3+ onto a biochar coming from the pyrolysis of dead Posidonia oceanica (BCP), a marine plant whose leaves accumulate in abundance on the sicilian coast, and onto its chemically activated forms with KOH (BBCP) and with H3PO4 (ABCP). The biochars were characterized through elemental analysis, surface area and average pore size measurements, ATR-FTIR and XRF spectra, and potentiometric measurements for the pHpzc determinations. At first, single batch adsorption experiments were carried out at different pH values below the pH of formation of low soluble hydrolytic species of REE (~ 6.5). Then, pH = 5.0 was chosen as the best pH in terms of REE recovery and kinetic and isotherm experiments were carried out at I → 0 mol L-1 and T = 298.15 K. The adsorption study of ABCP, the best REE adsorbent among those investigated, was therefore extended to evaluate the effect of ionic medium (NaNO3 0.1 mol L-1). The recyclability of ABCP adsorbent was also evaluated through column experiments in which HNO3 and EDTA 0.1 mol L-1 were chosen as extractant solutions. Inductively Coupled Plasma Optical Emission Spectroscopy was used to measure the REE concentration in the suspensions.