Synthesis of functional hydrochar from pinewood wastes through hydrothermal carbonization for removal of Pb(II) ions from aqueous solutions

Hydrothermal carbonization of pinewood wastes was performed to synthesize hydrochar for the removal of Pb(II) ions from contaminated solutions. The pinewood hydrochar was characterized using Fourier transform infrared, scanning electron microscopy, and X-ray diffraction. The results confirmed the porous nature of the hydrochar surface and the presence of various functional sites. The maximum Pb(II) uptake was recorded as 46.7 mg/g at pH 4.5. The experimental isotherm data exhibited a good fit to the Redlich–Peterson model, followed by the Langmuir and Freundlich models. The pseudo-first kinetics equation showed a better fit to Pb(II) kinetics data. Elution of Pb(II) ions from Pb(II)-loaded hydrochar was attempted using several elutants and the results indicated that 0.01 M HNO3 performed well with elution efficiency over 99.7%. Regeneration tests were aimed to regenerate and reuse pinewood hydrochar for five cycles and the hydrochar performed well in all cycles with only a 4.9% decrease in adsorption capacity at the end of the fifth cycle.