Effect of pyrolysis temperature on characteristics of biochars derived from different feedstocks: A case study on ammonium adsorption capacity

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 degrees C; at 300 degrees 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 degrees 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. (C) 2019 Elsevier Ltd. All rights reserved.