Properties of Eupatorium adenophora Spreng (Crofton Weed) Biochar Produced at Different Pyrolysis Temperatures

Pyrolysis temperature affects biochar properties, which in turn determine its application potential. Here, we examined the properties of crofton weed biochar (C-BC) produced at different pyrolysis temperatures of 300 degrees C, 400 degrees C, 500 degrees C, and 600 degrees C. We measured the yield, ash content, pH, iodine sorption value (ISV), and elemental composition of C-BC. We also characterized C-BC using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared, as well as its ability to remove Pb2+ and Cd2+ from aqueous solution. C-BC yield decreased with increasing pyrolysis temperature, whereas ash content and pH increased. ISV first increased at 300-400 degrees C and decreased at 500-600 degrees C. For C-BC produced at pyrolysis temperatures 300-600 degrees C (C-BC300 to C-BC600, respectively), H, N, and O content decreased, but C, Ca, Mg, P, and K content increased with increasing temperature. Water-soluble K+ content had the same trend as the K content, and water-soluble Ca2+, Mg2+, PO43-, NO3-, and NH4+ content decreased with increasing pyrolysis temperature. The (NO3-+NH4+), PO43-, and K+ content of C-BC was high, and the K+ content in C-BC600 was particularly high at up to 26,293.33 mg/kg. All C-BCs had a certain number of pore structures. Increasing pyrolysis temperatures decreased the amount of -OH, -COOH, aliphatic C-H, and polar C-O on the C-BC surface. As the pyrolysis temperature increased, calcium magnesium carbonate, calcium magnesium silicate, calcium magnesium phosphate, and potassium salt crystalline minerals gradually formed. The percentage of Pb2+ and Cd2+ removed increased with increasing pyrolysis temperatures. Overall, for C-BC, a low pyrolysis temperature was beneficial for producing a more porous biochar and increased content of water-soluble calcium, magnesium, nitrogen, and phosphorus, whereas high pyrolysis temperatures yield biochar that had high alkalinity, aromaticity, and stability, as well as heavy metal removal activity and water-soluble potassium content.