Feedstock and Temperature Influences in the Production of Biochar-Zero-Valent Iron Composites.

Biochar combined with zero-valent iron (BC-ZVI) has been demonstrated to improve remediation of water contaminated with trichloroethylene compared to ZVI alone.  Production of BC-ZVI by one-step pyrolysis from FeCl₃ treated biomass feedstocks is a convenient approach to producing such material; however the relationships between pyrolysis temperature and feedstock in the production of BC-ZVI composites are poorly understood. Understanding the influence of feedstock composition and pyrolysis temperature on the reduction of ferric iron (Fe³⁺) to ZVI during pyrolysis of biomass is critical to the production of BC-ZVI.  We report on the iron mineralogy of biochars produced by pyrolysis at 900 °C of cellulose, corn stover, dried distillers’ grain, red oak, and switchgrass feedstocks pretreated with FeCl₃.  Pyrolysis of feedstocks containing high levels of silicon (Si) and phosphorus (P) yielded fayalite and Fe phosphates and phosphides, which limited ZVI production efficiency and/or facilitated corrosion of ZVI.  Dispersion of ZVI phases on biochar surfaces and association with Si facilitated oxidation of ZVI due to greater accessibility to oxygen and enhanced corrodibility of ZVI in association with fayalite.  Feedstocks low in Si and P such as cellulose and red oak yield BC-ZVI suitable for environmental use.