Migration and transformation of heavy metals in boxwood sawdust biochar derived under different pyrolysis temperatures

Abstract In this study, biochar was prepared from boxwood sawdust under oxygen-limited conditions at 300, 400, 500, 600, 700 and 800 oC, respectively. The effects of different pyrolysis temperatures on the biochar physicochemical properties, migration and transformation of heavy metals (Cu, As, Ni, Cr and Pb) in the derived biochar were investigated. The results showed that the yield decreased, the ash content and pH of derived biochar increased with the increasing temperatures. The specific surface area of biochar was maintained at about 300 m2/g when the pyrolysis temperature was over 600 oC, and the highest total pore volume reached 2.0956 cm3/g− 1 at 800 oC. The concentrations of Cu, As, Cr and Pb increased by 20.35%-202.37% after pyrolysis. Meanwhile, heavy metals in bioavailable faction were partially transformed into relatively stable fractions with the increasing temperature. Furthermore, the potential environmental risks of heavy metals were reduced in the biochars derived at high temperature.