AN ANALYSIS OF ELEMENTAL BINDING POTENTIAL OF NATURAL PYROGENIC CARBON IN COMPARISON TO SYNTHETIC BIOCHAR

Pyrogenic carbon (PyC), also referred to as biochar, results from the pyrolysis of organic materials through their thermal decomposition at high temperatures in low oxygen environments. Synthetic biochar, which is produced in industrial or laboratory furnaces, is usually pyrolyzed under constant temperatures, typically up to 700 °C, for long periods of time (up to ~6 hours). PyC is also produced naturally during forest fires, where it burns at potentially higher temperatures (up to 1200 °C) and for very short periods of time (seconds to minutes for temperatures >300 °C). While synthetic biochars are well studied, there is scarcity of data pertaining to forest fire derived PyC with respect to its chemical reactivity and composition. Here we explored the physicochemical properties including the proton and metal adsorption potential of forest fire generated PyC (FF-PyC) collected from 4 locations within a recent forest fire along the Western slope of Mount Hunter, near Golden, British Columbia. We explored the binding capacity of both a model anion (species of SeO^2-) and cation (species of Cd²⁺) under a range of pH conditions (3-10) and then compared the findings to the adsorption potential of synthetically generated biochar produced from the same biomass. Additional properties that were measured and compared included the pH, CHNOS elemental composition, inherent types and number of reactive ligand sites, bonded molecules associated with ligand sites, and total surface reactivity. Fourier transform infrared (FTIR) and Raman spectroscopy was used to constrain the number and types of surface functional groups. Potentiometric titrations were performed and modelled with FITEQL to determine the acidity constants associated with each site and the total reactive surface area of both synthetic biochar and FF-PyC. Our results demonstrate higher surface reactivity associated with FF-PyC compared to synthetic biochar of an equivalent biomass. This both provides insight to the potential of FF-PyC as a vector for elemental transport in natural systems and also makes apparent the need to understand the pyrolysis conditions during a forest fire to improve our understanding of its role in global metals transport and cycling.