Qualitative assessment of biochar produced from low technology pyrolysis towards non-agricultural applications

Abstract

Biochar derived from sawdust of pine tree was prepared by using the simple and low-cost “kon-tiki” flame curtain pyrolysis, and the various properties of the prepared biochar were characterized in detail. The percentages of carbon, hydrogen, and nitrogen, were estimated at 78.0 wt. %, 2.6 wt. %, and 0.8 wt. % by the CHN measurement, and the percentage of ash content was presumed to be 5.8 wt. % from the residue of CHN measurement. The results of X-ray fluorescence (XRF) measurement and X-ray photoelectron spectroscopy (XPS) indicated that calcium is the main of inorganic element in the biochar. The N2 adsorption isotherm at 77 K of the biochar had low pressure hysteresis, which could mean that there are small pores the diameter of which is similar to the size of N2 molecule. The BET specific surface area (SBET) sample was 265 m2 g-1. The micropore volume estimated by Dubinin-Astakhov (DA) method of CO2 adsorption isotherm at 298 K was 0.26 cm3 g-1. After KOH activation the SBET value increased to 2500 m2 g-1. The performance of the KOH-activated sample was evaluated as the electrode of electric double layer capacitor (EDLC), which is a kind of electric energy storage device. The capacitance value of the sample was 190 F g-1 at 10 mA g-1. The pine tree biochar was separately treated with HNO3/H2SO4 and NaOH/H2O2 to produce two oxidized biochar samples. The performance of all 3 biochars was measured as adsorbent of uranium (IV). The adsorption data fitted best to pseudo-2nd order kinetics, indicating that adsorption is mainly controlled by chemisorption. The original biochar sample showed the highest adsorption capacity [714.1 mg g-1].