Characterization of biochar from pyrolysis of rice husk and rice straw

In this study biochar was prepared by pyrolysis of rice husk and rice straw. The effect of pyrolysis temperature (350, 450 and 550 °C) and the heating rate (10 and 50 °C/min) on the yield and properties of the biochar were investigated. The results indicated that ash content, fixed carbon content and the pH of the char increased while the volatile matters content and CEC decreased with the increase of pyrolysis temperature. Elemental analysis showed that the carbon content of the char increased while H and O decreased with raising temperature, resulting in the decrease of H/C and O/C ratios. The volatile matters released during the pyrolysis process creating pores in the carbonaceous materials which was revealed with the scanning electron microscope images. The results of pore volume from N₂ adsorption isotherm and Hg porosimetry showed that most of the biochar pores were macropores (≥50 nm). Although the rice husk biochar had higher specific surface area, micropore and mesopore volume, but the water adsorption capacity of the rice husk biochar was much lower than the rice straw biochar. Thus the macropore volumes may have a significant effect on the water adsorption capacity of the biochar.