An optimization strategy for apple charcoal reducing agents based on the physicochemical characteristics and CO2 gasification reactivity caused by carbonization temperature

This study investigated the preparation of charcoal reductants from apple tree pruning residues carbonized at temperatures ranging from 500 to 900 °C. The effects of carbonization temperature on industrial analysis composition, electrical resistivity and CO2 gasification reactivity were systematically evaluated using comprehensive characterization techniques, including elemental analysis, thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) specific surface area measurements and inductively coupled plasma (ICP) analysis, to clarify the influence of carbonization conditions on the structural and physicochemical properties of the resulting apple charcoal (PG). Results indicated that increasing the carbonization temperature enhanced the fixed carbon content and degree of graphitization, while reducing volatile matter, oxygen content, and electrical resistivity. Among the samples, PG-600 (PG carbonized at 600 °C) exhibits an optimal combination of high fixed carbon content (74.26 %) and moderate resistivity (27.8 kΩ cm). Thermogravimetric and kinetic analyses demonstrated that PG-600 exhibits higher reactivity than both petroleum coke (PC) and commercial charcoal (CC). The Boudouard gasification rate of PG-600 reached 1.2879 %/min·°C, exceeding that of CC (1.1383 %/min·°C). The apparent activation energy of PG-600 is 262.7 kJ/mol, which is lower than CC's 279.7 kJ/mol, further confirming its superior reactivity and CO2 gasification performance (achieving up to 99.6 % conversion within 10 min), balancing reactivity and structural stability suitable for industrial silicon smelting applications. This work provided a theoretical foundation and technical approach for the sustainable utilization of agricultural and forestry residues as high-performance carbonaceous reductants in metallurgical processes.