Effect of pyrolysis temperature on migration characteristics of heavy metals during biomass pyrolysis

In this study, the distribution, morphology, and migration characteristics of heavy metals in the products obtained at different pyrolysis temperatures were studied. With an increase in the pyrolysis temperature, the heavy metals were more inclined to volatilize into bio-oil and syngas, and the volatilization ratio was Zn > Pb > Cr > Fe > Ni > Mn > Cu. At pyrolysis temperatures below 400 °C, heavy metals were transformed from the migratory states (F1, F2, F3) to the residual state (F4). When the pyrolysis temperature exceeded 500 °C, heavy metals in migration states (F1, F2, F3) migrated to the bio-oil and syngas. The residual states (F4) of Fe, Cu, Ni, and Mn were stable. Although Zn and Pb in the residual state (F4) volatilized at high temperatures, the volatilization ratio was lower than that in the migratory state (F1, F2, and F3). At a pyrolysis temperature of 900 °C, the potential risk factor (RI) of heavy metals decreased from 448.67 to 5.21, significantly reducing the environmental risk.