Waste Plastics Complement Biochar: Innovative Approach in Curbing Toxicants (KCN/NaCN) in N-Containing Biochar

Abstract

Alkaline metal cyanide (MCN) such as KCN or NaCN in N-containing biochar is a new obstacle for sustainable use of biochar. However, plastic waste can be utilized for solving these highly toxic substances MCN. In this work, plastic performed outstandingly in MCN elimination by preventing its parent formation (MOCN, e.g., KOCN) via complexation of alkaline metals and N. The CN– content in biochar was completely inhibited by co-pyrolysis with specific plastics from ∼30 000 to ∼0 mg/kg. Polyvinyl chloride, polytetrafluoroethylene, and triphenyl phosphate, which contain heteroatoms such as Cl, F, and P, can seize K atoms from biomass, resulting in the production of KCl, KF, K3PO4, and KPO3 instead of the KOCN (precursor of KCN). Furthermore, owing to the lack of ligand metal, N tended to dope into the biochar skeleton. Both reactions affected by plastic significantly led to the failure of MCN formation. After MCN controlled, an increase in N content and aromaticity and a decrease in the surface area of biochar were simultaneously observed. Unquestionably, biochar has become more environmentally friendly after MCN inhibition by plastic, as confirmed by the bio-assessment of the resultant biochar.