Biochar from byproduct to high value added material – A new adsorbent for toxic metal ions removal from aqueous solutions

An activated biochar coming from pyrolysis of dead Posidonia oceanica residues has been tested as adsorbent material for Cd2+, Pb2+and Cu2+ions. The biomass, the activated and the non activated biochars were previously characterized by using several instrumental techniques. The pH of metal ion solution in kinetic and thermodynamic adsorption experiments was fixed at 5 whilst, the dependence on ionic medium, ionic strength and temperature have been evaluated carrying out batch experiments at different experimental conditions. Differential Pulse Anodic Stripping Voltammetry and Inductively Coupled Plasma Optical Emission Spectroscopy have been used to measure the metal ion concentration in the solutions. Several kinetic and isotherm equations were used to fit experimental data. The thermodynamic parameters ΔG, ΔH and ΔS of Pb2+adsorption process were calculated by using Gibbs and van't Hoff equations. A speciation study of the Pb2+ion was also done in order to evaluate the influence of ionic medium and ionic strength on the adsorption process. Information about adsorption mechanism was obtained from the analysis of thermodynamic parameters of adsorption and of the results of metal ions speciation and biochar characterization.