Study on the Migration Pattern of Heavy Metals, Environmental Risks, and Optimization of Conditions During Pyrolytic Remediation Plants by Two‐Step Pyrolysis

Remediation plants are crucial for treating heavy metal‐contaminated soil and serve as biomass resources. Pyrolysis effectively utilizes these plants; however, these conditions significantly affect heavy metal migration. This study employed an orthogonal experimental design to investigate the effects of heating rate, initial temperature, and residence time on heavy metal migration during a two‐step pyrolysis process. The results demonstrated that the heating rate predominantly influenced the distribution of heavy metals in biochar and bio‐oil, as well as the leaching risk associated with biochar. The initial temperature primarily influenced the heavy metals content in syngas. A slower heating rate decreased the retention of heavy metals in biochar but enhanced their volatilization into bio‐oil and syngas. Conversely, higher initial temperatures reduced heavy metals in syngas but increased them in bio‐oil and biochar. Optimal two‐step pyrolysis conditions were a heating rate of 15 °C/min, an initial temperature of 400 °C, and a residence time of 45 min. Compared with one‐step pyrolysis, two‐step pyrolysis can further reduce the environmental risks of biochar.