Spectroscopic Characterisation and Elemental Composition of Biochars Obtained from Different Agricultural Wastes

Abstract

The use of biochar (BC) has an environmental importance in terms of climate change, soil fertility, waste management and energy generation. The purpose of this study was to reveal some of the structural characteristics of BC produced from agricultural wastes by employing spectroscopic techniques within a short time frame. The BCs were produced via slow pyrolysis at 300°C from four feedstocks: tea waste (TW), hazelnut husk (HH), rice husk (RH) and poultry litter (PL). The pH of plant-derived BC was alkaline (pH: 7–9), and the pH of manure-derived BC was strongly alkaline (pH: 10.1). PLBC has the highest (4.67 dS m−1) electrical conductivity (EC) when compared to other BC materials. According to the X-ray fluorescence (XRF) analysis method, organic compound contents of TWBC and HSBC were found to be higher than the other two BCs, while the other two BCs (RHBC and PLBC) were richer in mineral content. TWBC and HHBC were composed of more mineral elements when compared to RHBC and PLBC, but the latter two were still rich in minerals. The surface area of RHBC was found higher (12.9 m2 g-1) than other BC materials. According to the X-ray fluorescence (XRF) analysis method, the total element content of PLBC was found higher than the other BCs. In addition, the silicon (Si) content of RHBC was considerably higher (16.4%). In PLBC’s XRD diagram: quartz (SiO2) at 3.41 (A); calcite (CaCO3) at 3.96, 2.94 and 1.91 (A); sylvine (KCl) at 3.06 and 1.85 (A); and whitlockite ([Ca, Mg]3 [PO4]2) at 2.78 and 2.17 (A) were found. In HHBC and RHBC diagrams, partially crystallized carbon (CryC) peaks were mainly observed  between 1.20 and 2.34 (A), and cristobalite peaks (i.e., amorphous SiO2) were observed at 3.91  and 3.40 (A).