Pyrolysis temperature induced changes in characteristics and chemical composition of biochar produced from conocarpus wastes

► Conocarpus wastes were pyrolyzed at different temperatures of 200, 400, 600 and 800°C. ► Biochar produced at high pyrolysis temperature enjoys higher carbon stability compared to that obtained at low temperature. ► Biochar produced at high pyrolysis temperature may possess a higher carbon sequestration potential when applied to the soil. Conocarpus wastes were pyrolyzed at different temperatures (200–800°C) to investigate their impact on characteristics and chemical composition of biochars. As pyrolysis temperature increased, ash content, pH, electrical conductivity, basic functional groups, carbon stability, and total content of C, N, P, K, Ca, and Mg increased while biochar yield, total content of O, H and S, unstable form of organic C and acidic functional groups decreased. The ratios of O/C, H/C, (O+N)/C, and (O+N+S)/C tended to decrease with temperature. The data of Fourier transformation infrared indicate an increase in aromaticity and a decrease in polarity of biochar produced at a high temperature. With pyrolysis temperature, cellulose loss and crystalline mineral components increased, as indicated by X-ray diffraction analysis and scanning electron microscope images. Results suggest that biochar pyrolized at high temperature may possess a higher carbon sequestration potential when applied to the soil compared to that obtained at low temperature.