Effect of deashing on physico-chemical properties of wheat and rice straw biochars and potential sorption of pyrazosulfuron-ethyl

Abstract

Wheat (WBC) and rice straw biochars (RBC) prepared at 400 and 600 °C and their deashed counterparts were characterized for their physico-chemical properties using CHN analysis, Brunauer–Emmett–Teller (BET), X-ray fluorescence (XRF), scanning electron microscopy (SEM), 13C-nuclear magnetic resonance (NMR), X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) techniques. Pyrazosulfuron-ethyl sorption data on normal and deashed biochars could be well fitted to the Freundlich model. The characteristics of biochars and their adsorption capacities for pyrazosulfuron-ethyl were affected by the pyrolysis temperature and nature of feedstock. Rice biochars had higher sorption capacities than the wheat biochars. Deashing of biochars further enhanced their herbicide adsorption potential by a factor of 2–3. Sorption of herbicide on both normal and deashed biochars was concentration dependent (1/n < 1) and decreased with increase in the herbicide concentration in solution, indicating a saturation of sorption sites. The non-linearity of the isotherms increased with increasing pyrolysis temperature and deashing. Furthermore, adsorption of pyrazosulfuron-ethyl was affected by the pH, surface area and pore volume of biochars. Results of this study suggested that the mineral fraction of biochars significantly affected pyrazosulfuron-ethyl sorption.