Characterization of char generated from solar pyrolysis of heavy metal contaminated biomass

Solar pyrolysis of raw and heavy metals (HMs) impregnated willow was performed at different temperatures (600, 800, 1000, 1200, 1400 and 1600 °C) with heating rate of 50 °C/s. CHNS, ICP-OES, SEM-EDX and BET were employed to investigate the effects of temperature and HMs contamination on char properties. The results indicated that a more ordered and aromatic char was formed with increasing pyrolysis temperature. Char carbon contents increased from 70.0% to 88.4% while hydrogen and oxygen contents declined. Char BET surface area firstly increased from 5.3 to 161.0 m2/g with rising the temperature from 600 to 1000 °C, then decreased at higher temperatures due to plastic deformation. Pyrolysis caused alkali and alkaline-earth metals (A&AEMs) enrichment in char as temperature increased from 600 to 800 °C, then their content decreased at higher temperatures. The presence of Cu or Ni led to the decrease of hydrogen and oxygen contents and significant increase of Ni or Cu in char compared with those in raw willow char. Besides, Raman and BET analysis showed that contaminated willow char had a higher ratio of G band area to the integrated area (IG/IAll) and bigger BET surface area than raw material indicating a more organized and porous structure of the char.