Effect of Pyrolysis Temperature on the Physicochemical Properties and Structural Characteristics of Agricultural Wastes-Derived Biochar

The efficient handling of agricultural waste is rapidly gaining worldwide recognition. This study analyzes the impact of three distinct pyrolysis temperatures (250, 300, and 350 °C) on the physicochemical properties of the biochar produced from rice husk, sugarcane bagasse, and groundnut shells with a fixed pyrolysis time of 3 h. The influence of the pyrolysis temperature was assessed by calculating the biochar yield, electrical conductivity (EC), pH, proximate analysis, and ultimate analysis. Further structural and morphological characterization was performed using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), ζ-potential analysis, and X-ray diffraction (XRD). The physicochemical properties are influenced by the feedstock materials and the temperature during the pyrolysis process. Increasing the pyrolysis temperature leads to a rise in the ash content (39.12%), fixed carbon content (82.4%), EC (0.56 to 4.567 dS/m), and pH (4.0 to 7.7). In contrast, yield, moisture, and volatile matter exhibited a decreasing trend; biochar yield dropped by more than 50% across all feedstocks; moisture content diminished by up to 3.4%, and the volatile matter decreased to 6.9% at elevated temperatures. Elemental analysis indicated the highest carbon content at 350 °C in all samples, increasing up to 75.56%, while elements such as nitrogen, hydrogen, sulfur, and oxygen content and atomic ratio decreased. Inductively coupled plasma mass spectrometry (ICP-MS) analysis shows a higher concentration of minerals, such as potassium, calcium, and magnesium, at higher temperatures. SEM results indicate a well-defined pore structure at moderate thermal conditions of 300 and 350 °C. FTIR and XRD characterization suggests the presence of various functional groups and crystalline structures, respectively. Biochar exhibited more negative ζ-potential values at higher temperatures (350 °C), ranging from -36.4 to -59.3 mV, indicating a high electrostatic interaction with cations, heavy metals, and pollutants. This research offers a unique and comprehensive analysis of three different agricultural feedstocks subjected to moderate pyrolysis conditions, providing new insights into improving biochar properties for soil remediation and environmental sustainability.