N-rich hydrochar derived from organic solvent as reaction medium generates toxic N-containing mineral in its pyrochar

摘要

Low-grade hydrochar is often thermally activated to produce pyrochar. However, the interaction between inherent metals and N element during hydrochar activation process has never been considered. Present study revealed that a highly toxic N-containing mineral (MCN, M: metal) can be formed in N-rich hydrochar-based pyrochar via N rearrangement and subsequent carbothermal reactions. This atypical hydrochar is mainly produced from organic wastes with K_2CO_3 or Na_2CO_3 (such as food waste) in an organic solvent medium. The CN~- concentration of studied pyrochar can reach to 9807 mg/kg, which is mainly determined by content and type of metal in hydrochar. The low N conversion rate (＜4.2%) indicates that formation of MCN is independent of N content in hydrochar. Essentially, formation of MCN can be significantly inhibited by FeCl_3 via the anionic interactions between Fe and K salt. This discovery can likely offer a new guide for the application of N-rich hydrochar-based pyrochar.