Assessment of Pistachio Shell Biochar Quality and Its Potential for Adsorption of Heavy Metals

Abstract

In the present study pistachio shells obtained from Aegina island, Greece, were subjected to slow pyrolysis for the production of biochar. Pyrolysis was carried out over a temperature range of 250–650 °C for 1 h using a heating rate of 10 °C min−1 and the quality of the produced biochar was assessed by evaluating its main properties, namely pyrolysis yield, pH, volatile matter, char, fixed carbon, ash and C, H, S, N content. Thermogravimetric analysis, X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy were used for the identification of the morphology and structure of the produced biochar. Finally, the potential of biochar to remove heavy metals, namely Pb and Cu, from synthetic solutions was investigated. A kinetic study indicated that sorption can be very well described by the pseudo-second order kinetic model, while simulation of the sorption isotherms provided better fit for the Freundlich model. The experimental data show that Pb is adsorbed more efficiently compared to Cu in all biochars, while the highest % adsorption for both heavy metals, almost 100 %, is shown for 10 g L−1 biochar produced after pyrolysis at 550 °C when the initial Pb and Cu concentration in solution was 15 mg L−1.