Submitted to: Journal of Powder Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/4/2012
Publication Date: 9/1/2012
Citation: Peterson, S.C., Jackson, M.A., Kim, S., Palmquist, D.E. 2012. Increasing biochar surface area: optimization of ball milling parameters. Journal of Powder Technology. 228(1):115-120.
Interpretive Summary: Biochar is a renewable source of carbon that has the potential to be used as a substitute for activated carbon in many materials used to absorb liquids or gases. In order to do this, however, it must have a high surface area. Surface area is increased in carbon feedstocks (many of which are petroleum-based) by 'activating' it by either chemical means (like strong alkali), or physical means (like steam). In this work two different types of ball milling methods were tested to see how effectively the surface area of the biochar could be improved without using traditional chemical or physical means, and what parameters controlled this. The second type of ball milling method attempted was a relatively recently developed technique using common sodium chloride crystals to assist in milling, the advantage being that the salt crystals are reduced in size throughout the milling procedure, making an even more effective grinding media that can increase surface are more effectively. This salt-assisted milling method was found to effectively increase the micropore surface area (which is important in filter media applications) of biochar. This information will be beneficial to those who use wet-milling techniques with carbon feedstocks and benefit agricultural producers of biochar.
Technical Abstract: Biochar produced from corn stover is a renewable, plentiful source of carbon that is a potential substitute for carbon black as rubber composite filler and also as 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 and more than twice that of a carbon black control. Additionally, the method of salt-assisted dry-milling was tested and found to increase the surface area of biochar only moderately, but was superior for increasing the micropore surface area of the biochar.