Biochars derived from giant reed (Arundo donax L.) with different treatment: characterization and ammonium adsorption potential

The adsorption characteristics of Arundo donax L.(AD) biochars for ammonium(NH4+-N) were investigated. Absorbents were characterized through scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy analyses. AD-500 and AD-800 were produced from raw AD and pyrolyzed from room temperature to 500 and 800 °C, respectively. PD-500 was prepared by impregnating AD with a mild alkali solution and pyrolyzing from room temperature to 500 °C. The feasibility of the use of AD-500, AD-800, and PD-500 removing NH4+-N from an aqueous solution was examined. The adsorption system followed the pseudo-first-order model. Results showed that the adsorption capacities of AD-biochars for NH4+-N were enhanced after the final pyrolysis; temperature was increased or the mild alkali pretreatment was administered. When the initial NH4+-N concentration was changed from 4 to 8 mM, the NH4+-N sorption capacity of the biochar increased from 23 to 51%, with the final pyrolysis temperature increasing from 500 to 800 °C. The improved ratios were 12 to 33% when the biochar was prepared at 500 °C after the mild alkali pretreatment, and NH4+-N sorption was enhanced due to ion exchange in the PD biochar.