Influence of pyrolysis temperature on the properties of biochar derived from boxwood sawdust and environmental risk of heavy metals
Biochar was prepared from boxwood sawdust by pyrolysis under anoxic conditions at 300,400,500,600,700 and 800℃,respectively.The effects of pyrolysis temperature on the physicochemical properties of biochar and the migration and transformation of heavy metals(Cu,As,Ni,Cr and Pb)were investigated.The results showed that the biochar yield decreased significantly with the increase of pyrolysis temperature,while the ash content and pH value increased gradually.The highest specific surface area of biochar was 325.3530 m2/g while the microporous volume reached 2.0956 cm3/g at a pyrolysis temperature of 800℃.The content of most of the heavy metals(Cu,As,Cr and Pb)in the prepared biochar increased by 20.35%～202.37%compared with that in the feedstock.Meanwhile,the heavy metals in the biochar were transformed from unstable to stable forms with the increase of pyrolysis temperature,in which the percentage of Cu,Ni,Cr and Pb in the residual form was obviously enhanced with the increase of pyrolysis temperature,and the high-temperature pyrolysis significantly reduced the potential ecological risks of the heavy metals in the biochar.
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