Bio-char from dead Posidonia oceanica residues as adsorbent towards toxic metal ions

Recently, the pyrolysis of biomass from different algal species and from the Mediterranean sea plant Posidonia oceanica have been proposed for renewable fuel production with a maximum oil yield of 54.97% at 500°C, and high heating values of 24-32 MJ kg−1. The pyrolysis produces a large amount of bio-char and the accumulation of this byproduct may cause solid waste pollution problems. Although the composition and properties of bio-char depend on the raw material and on the carbonization process, it is on average composed of amorphous carbon with a highly functionalized surface, which makes it reactive towards inorganic and organic compounds. Considering the reactivity of bio-char, this pyrolysis by-product could be converted in a high value added material by using it as adsorbent towards toxic metal ions and other organic and inorganic pollutants in decontamination processes. In this context, the bio-char coming from the pyrolysis of local waste biomass (the dead Posidonia oceanica residues) was chemically activated and investigated for potential use as adsorbent of toxic metal ions. The activated and non activated bio-chars were characterized by using different techniques. Then, their adsorption ability towards several toxic metal ions was studied carrying out several experiments with metal ions solutions at pH = 5, containing NaNO3 or NaCl backgrounds, at different ionic strengths and temperatures. The residual metal concentration in aqueous solutions during the equilibrium experiments was measured by Differential Pulse Anodic Stripping Voltammetry (DP-ASV) and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) techniques. Langmuir and Freundlich isotherm equations were used to fit the experimental data.