| Summary: | The eco-risk of heavy metal has been a constraint to the resource utilization of sludge and sludge biochar, which depends mainly on its chemical form. In recent years, the researches on the speciation and distribution of the heavy metals in sludge and its biochar have received extensive attention and have become a research hotspot in environmental science. In this paper, the technical characteristics of pyrolysis and hydrothermal carbonation (HTC) are discussed. Secondly, the contents and speciations of heavy metals in municipal sewage sludge and biochar were analyzed. Finally, the reaction mechanisms of heavy metals during pyrolysis and HTC were summarized. This paper comprehensively compares the differences in the form transformation of heavy metals in these two processes, which offer an important references for further researches on the immobilization of heavy metals in pyrolysis and HTC.
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