Thiol-modified olive-stone biochar preparation for Hg(II) removal from aqueous solutions

Abstract

Mercury (Hg) is a heavy metal whose toxicity poses significant environmental and health risks. Utilising biochar prepared from biomass waste is a straightforward and effective method for removing mercury from water. This research centred on producing a thiol-functionalised biochar derived from olive-stone waste for the removal of mercury (II) from aqueous solutions. Characterisation analyses confirmed successful functionalisation. The biochar, despite having a limited specific surface area (4.14 m2/g) due to raw material nature and pyrolysis conditions, exhibited a notable ability for mercury (II) adsorption, primarily attributed to the thiol-modified surface. Adsorption was assessed using a 23 factorial design, with the variables being adsorption time, biochar dose and initial mercury (II) concentration in the solution. Biochar dose emerged as the most influential factor, followed by adsorption time and, lastly, initial mercury (II) concentration. The peak removal efficiency of the model stood at 98.19%. The kinetics aligned with the pseudo-first-order and intraparticle diffusion models, suggesting a surface adsorption mechanism coupled with pore diffusion. This work accentuates the potential of olive-derived biochar, when thiol enhanced, in treating aqueous systems contaminated with mercury (II).