Pyrogenic carbon (PyC), commonly referred to as biochar, results from the thermal decomposition of organic materials at high temperatures and in low oxygen environments (known as pyrolysis). Commercial biochar produced in industrial or laboratory furnaces, is pyrolyzed under constant temperatures, typically up to 700 °C, for long periods of time (up to ~6 hours). Similarly, biochar can be produced naturally during forest fires, where it burns at higher temperatures (up to 1200 °C) and for short periods of time (176 s for temperatures &gt;300 °C). While the chemical reactivity and composition of commercial biochars are well studied, there is scarcity of data pertaining to forest fire derived analogues. Here we investigated the differences in physicochemical properties of biochar produced during a natural forest fire with biochar produced using conventional laboratory furnace conditions. Both unburnt biomass and forest fired derived PyC (FF-PyC) was collected from 5 locations within a recent forest fire along the Western slope of Mount Hunter, near Golden, British Columbia. The physicochemical properties of the FF-PyC were compared to tube furnace produced biochar made from the unburnt biomass from the site of the fire. A range of properties including the porosity, specific surface area, total surface reactivity, metal adsorption potential, CHNOS elemental analysis, anion exchange capacity, cation exchange capacity, mobility, as well as extracted nanoparticles inherent to the PyC were studied in both the laboratory biochar and FF-PyC, and compared. Our results provide insights into the conditions needed to produce biochar equivalent to FF-PyC in a laboratory setting, critical to understanding the factors in a fire that control carbon reactivity and PyC colloidal release into soils and groundwater.

Comparison of the physicochemical properties of forest fire generated pyrogenic carbon and synthetic biochar

ACS Spring 2022

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