Increasing biochar surface area: Optimization of ball milling parameters

Biochar produced from corn stover is a renewable, plentiful source of carbon that is a potential substitute for binder/filter media for water or beverage purification applications. However, to be successful in these applications, the surface area of the biochar must be maximized. In this work, a planetary ball mill was used to increase the surface area of the biochar, and various milling parameters were examined to see which had the largest effect on surface area. The weight ratio of milling media to biochar and the mass of solvent used in wet-milling were the most important milling parameters in maximizing surface area, increasing it by a factor of approximately 60 over unmilled biochar. Additionally, the method of salt-assisted dry-milling was tested and found to increase both the total and micropore surface areas of biochar, but not as effectively as wet-milling methods. For salt-assisted milling, a 50:1 mass ratio of YSZ grinding media:NaCl was optimal for maximizing both the total and micropore surface areas of the biochar.