How do heavy metals migrate during hydrothermal carbonization of woody waste?

Abstract Licorice extracted from the Chinese medicine residue (CMR) was chosen as the experimental material to discuss the migration mechanism of heavy metals during hydrothermal carbonization (HTC) of woody waste. The results show that the contents of heavy metals in hydrochars are increased during HTC process, and can be divided into five groups according to their evolution trend during this process. The heavy metals in the second group, including Sb, Mo, Ga, Ni, Co, and Cr, are more significantly affected by HTC duration than the other four groups. The fatty side chains and oxygen‐containing side chains are removed with an increasing aromatization degree during HTC process. The second group heavy metals are mainly distributed in aromatic carbon lamellae or adsorbed on the surface of aromatic structure.