Insights into water quenching effects on ash removal characteristics, physicochemical properties, and combustion performance of straw-derived pyrochar

Minimizing the contents of detrimental elements and associated ash components in straw-derived pyrochar (PC) is critical for mitigating ash-related problems in metallurgical applications. This study innovatively employs water quenching (WQ) to improve the leaching of these components and systematically investigates its effects on the physicochemical properties and combustion behavior of PC prepared at 400 °C (PC400), 600 °C (PC600), and 800 °C (PC800). Results show that, due to superior leaching kinetics and thermodynamics, WQ significantly enhances the leaching of detrimental elements and other ash components from PC, with PC loss mainly attributed to reduction ash. WQ increased oxygen/hydrogen content and consequently elevated volatile matter in PC400 and PC600, while reducing volatiles in PC800 due to gasification of amorphous hydrocarbons. The treatment compromised pore structure development in PC400 but enhanced micropore formation and specific surface area in PC600 and PC800. Moreover, WQ disrupted ordered aromatic structures, decomposed alkane chains through steam interaction, and promoted phenolic etherification. Ash removal during WQ increased combustion activation energy, enhancing PC's compatibility with ironmaking, with 600 °C identified as the optimal quenching temperature. This work presents a novel strategy for pyrochar upgrading.