Influence of pyrolysis conditions on the properties and Pb2+ and Cd2+ adsorption potential of tobacco stem biochar

Abstract

Converting biomass into biochar is a smart recycling strategy. Biochar was produced from tobacco stems at temperatures of 400 °C, 500 °C, 600 °C, and 700 °C and holding times of 1.5 h, 2 h, 2.5 h, and 3 h. Its properties and adsorption capacities for Pb2+ and Cd2+ were evaluated. While the yield decreased, pH, phosphorus, potassium, ash, and surface area increased with increasing pyrolysis temperature and holding time. Nitrogen, volatile matter, and pore diameter decreased as the temperature increased, with an irregular effect of the holding time. A peak C content (652 g/kg) was recorded at 600 °C (2 h). The highest values obtained for the N, P, and K content were 25.6 g/kg (400 °C and 2 h), 7.82 g/kg and 168 g/kg (600 °C and 3 h), respectively. The heavy metal contents were within tolerable limits. The highest surface and micropore areas of 50.6 and 57.1 m2g-1 respectively, were obtained at 700 °C (3 h). The biochar had a wide range of aliphatic and aromatic C functional groups. The highest adsorption percentages of Pb2+ and Cd2+ (44.5 % and 38.3 %, respectively) by biochar produced at 700 °C (3 h) signified its suitability for heavy metal adsorption. These properties made the biochar a suitable soil amendment.