Anion Exchange Capacity of Biochar.

Anion Exchange Capacity of Biochar

Michael Lawrinenko¹ and David Laird¹

¹Department of Agronomy, Iowa State University, Ames, IA 50011.

Soil application of biochars with appreciable anion exchange capacity (AEC) may reduce anionic nutrient leaching losses from agricultural and horticultural systems while enhancing N and P use efficiency.   Previous studies have shown limited and short-lived AEC in biochars, however no studies have systematically investigated the functional groups responsible for biochar AEC or the influence of thermochemical production conditions on the AEC of biochars. 

We found that biochar AEC increases with decreasing pH, pyrolysis at 700^◦C yielded biochars with higher AEC than pyrolysis at 500^◦C, and that there was no obvious effect of feedstock as alfalfa meal, corn stover, and cellulose biochars had similar AEC values.  Characterization of the studied biochars using elemental analysis, FTIR spectroscopy, X-ray diffraction, and N₂-BET surface area analysis provide no specific evidence for the nature of the functional groups on the surfaces of biochar responsible for AEC.  However, significant AEC was measured for biochars produced from pure cellulose, which is composed almost exclusively of C, H, and O atoms and had negligible ash content.  From this observation, it is hypothesized that AEC in this biochar is due to an O containing surface functional groups.