Effect of pyrolysis temperature on characteristics of biochars derived from different feedstocks: A case study on...

Physiochemical properties of biochars derived from different feedstock materials (rice straw, Phragmites communis, sawdust and egg shell) at different pyrolysis temperatures were analyzed, and adsorption capacities of ammonium (NH₄⁺) on the biochars were investigated. The results show a clear effect of pyrolysis temperature on physicochemical properties of the biochars, including specific surface area, pH, and zeta potential. Consequently, biochars derived from the studied feedstocks at the selected temperatures exhibited different capacities to absorb NH₄⁺. Highest NH₄⁺ adsorption capacities were associated with biochars of rice straw (4.2 mg/g) and sawdust (3.3 mg/g) produced at 500 °C; at 300 °C observed NH₄⁺ adsorption capacity was lower and highest figures were derived from the biochars of Phragmites communis (3.2 mg/g) and egg shell (2.2 mg/g). For all feedstocks, biochars produced at 700 °C showed the lowest NH₄⁺ adsorption capacity. Our results suggest that zeta potential and C/H ratio, rather than surface area, are the most important factors in determining NH₄⁺ sorption potential of biochars.