|Niandou, Mohamed A|
|Novak, Jeffrey - Jeff|
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/29/2013
Publication Date: 3/1/2013
Citation: Niandou, M.S., Novak, J.M., Bansode, R.R., Yu, J., Rehrah, D., Ahmedna, M. 2013. Selection of pecan shell based activated carbons for removal of organic and inorganic impurities from simulated well-water. Journal of Environmental Quality. 42(3): 902-911. Interpretive Summary: The annual production of nutshell wastes in the USA is very large. In fact, almost 1.5 million tons of nutshell wastes are produced. While some of the nutshell wastes are burned as a fuel source, much of the shell wastes are processed into activated carbon for use by the water purification industry. Pecan shell wastes are plentiful in the southeastern USA, so this material can be processed into activated carbon material. Activating carbon from pecan shell waste is complicated, and the conditions needed to produce material capable of sorbing different pollutants have not been fully explored. Our research was designed to process pecan shell wastes into activated carbon and then determine which processing conditions caused the greatest ability to sorb chemical pollutants. Laboratory experiments revealed that acid and base-like chemicals along with steam treatment, and pyrolyzed at high temperatures (700 degree Celsius) were particularly effective at modifying the surface chemistry of the activated pecan shell carbons. In laboratory sorption studies, the activated pecan shell material was mixed with inorganic and organic chemicals that are known drinking water pollutants. For comparison, additional sorption experiments were conducted using commercially available activated carbon. Base-activated material was more effective at sorbing the pollutants than the commercially available sorbent material. Our results showed that pecan shell wastes can be processed, under the proper conditions, into activated carbon capable of effectively sorbing example pollutants in drinking water sources.
Technical Abstract: Activated carbons are a byproduct from pyrolysis and have value as a purifying agent. The effectiveness of activated carbons is dependent on feedstock selection and pyrolysis conditions that modify its surface properties. Therefore, pecan shell-based activated carbons (PSACs) were prepared by soaking shells in 50% volume per volume phosphoric acid or 25-50% of potassium hydroxide, sodium carbonate followed by pyrolysis at 400-700 degrees Celsius under a nitrogen atmosphere. Physically activated PSACs were produced by pyrolysis at 700 degrees Celsius under nitrogen followed by activation with either steam or carbon dioxide at 700-900 degrees Celsius. Physicochemical, surface and adsorption properties of the PSACs were compared to two commercially available activated carbons. PSACs average yield was about 20 and 34% for physically-activated and chemically-activated carbons, respectively. Acid-activated carbons exhibited higher surface area, bulk density, and lower ash content compared to steam or carbon dioxide activated carbons and the two commercial products. Base-activation led to the development of biochar with moderate to high surface area with surface charges suitable for adsorption of anionic species. Regardless of the activation method, PSACs had high total surface area ranging from 400 to 1,000 meters squared per gram, better pore size distribution, and more surface charges than commercial samples. Our results also showed that PSACs were effective in removing inorganic contaminants such as copper and nitrate as well as organic contaminants such as atrazine and metolachlor. This study showed that pyrolysis conditions and activation had a large influence on the PSACs surface characteristics, which can impact its effectiveness as a custom sorbent for targeted water contaminants.