ADSORPTION OF PB~(2+) ON MAGNETIC MODIFIED HEMP BIOCHAR PREPARED USING MICROWAVE- ASSISTED PYROLYSIS

摘要

Magnetic modified hemp biochar with an aim of high adsorption capacity and rapid adsorption rate was prepared by two simple steps using microwave pyrolyzed biochar. This was investigated as a potential green adsorbent for lead remediation from wastewater in a batch-mode experiment. The 150 - 300 urn biochar particles obtained from microwave-assisted pyrolysis of 1.5 kg hemp biomass batch at an average temperature of 600°C were first impregnated with H_2O_2 and then magnetized by mixing aqueous biochar suspensions with aqueous Fe~(3+)/Fe~(2+) solutions. The composition, morphology and surface chemistries of this magnetic biochar was examined by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), vibrating sample magnetometry (VSM) and BET surface area (S_(BET)). The S_(BET) of the magnetic hemp biochar is 83.76 m~2 g~(-1). Batch sorption studies were performed for a 50 mg L~1 lead solution at room temperature and pH 5.5 using 0.02 g of the magnetic adsorbent in 20 ml solution for 2 hours. The experimental results have shown that the adsorption capacity of this magnetic adsorbent for Pb~(2+) is 43.97 mg g~(-1), about 87.94% removal within the 2 hours. Both pseudo-second-order and pseudo-first-order kinetic model could predict the adsorption and desorption kinetic process on the modified sorbent. EDX analysis are used to show the mechanisms for the adsorption of Pb~(2+) onto the adsorbent via mainly ion exchange. The Freundlich, Temkin and Langmuir models are used to predict the sorption isotherm in the system. The as-prepared magnetic hemp sorbent demonstrated a potential in heavy metal wastewater treatment.