Effect of pyrolysis temperature on eucalyptus wood residues biochar on availability and transport of hexazinone in soil

Abstract

Biochar is a material with the ability to adsorb pollutants, and this capacity depends on pyrolysis temperature. In this research, the effect of pyrolysis temperature (650, 750, 850, and 950 °C) on the properties of biochar derived from eucalyptus wood and its influence on the sorption/desorption, leaching, and distribution of hexazinone in soil were evaluated. Sorption and desorption were investigated using the batch balance method, and experiments were conducted to assess hexazinone leaching (in glass columns) and distribution (in biometric flasks). The pyrolysis temperature of 950 °C increased (nitrogen + oxygen)/carbon and ash ratios and produced a biochar with greater sorption coefficient and less desorption coefficient of hexazinone. The pyrolysis temperature of 650 °C produced an aliphatic material, with less sorption and greater desorption. Biochars produced at pyrolysis temperatures of 850 and 950 °C completely prevented leaching of the herbicide in soil. The total hexazinone unavailable (mineralized + non-extracted residue) in the biochar system produced at pyrolysis temperatures of 850 °C (46%) and 950 °C (49%) was higher compared to that produced at 650 °C (33%) and 750 °C (42%). Despite this, the addition of biochar did not alter hexazinone mineralization but reduced the availability of the product in the environment due to the greater amount of non-extracted residue, thus reducing the risk of environmental contamination by this herbicide.