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United States Department of Agriculture

Agricultural Research Service

Research Project: THERMOCHEMICAL PROCESSING OF AGRICULTURAL WASTES TO VALUE-ADDED PRODUCTS AND BIOENERGY

Location: Commodity Utilization Research

Title: Uncovering surface area and micropores in almond shell biochars by rainwater wash

Authors
item Klasson, K Thomas
item Uchimiya, Sophie
item Lima, Isabel

Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 12, 2014
Publication Date: September 1, 2014
Citation: Klasson, K.T., Uchimiya, M., Lima, I.M. 2014. Uncovering surface area and micropores in almond shell biochars by rainwater wash. Chemosphere. 111:129-134.

Interpretive Summary: Biochars have been considered for adsorption of contaminants in soil and water, as well as conditioning and improving soil quality. One important property of the biochar is surface area in the pores of the biochar. Biochars were created from almond shells from two almond varieties with different ash content in the shells. The pyrolysis was performed in an inert nitrogen atmosphere at 650 and 800°C for 40 to 240 min. Characterization of the biochars showed that significant surface area (based on nitrogen adsorption isotherms) developed at the higher temperature and at pyrolysis times of 120 min and longer. Washing the materials in synthetic rainwater removed inorganic ash and exposed additional surface area, particularly in small-diameter pores. When results from low-ash almond shell biochars were compared with high-ash almond shell biochars, it was found that the pore distribution was more uniform for the high-ash starting material and almost independent of pyrolysis time or washing. The biochars from the low-ash starting material (Padre almond variety) showed a much greater dependence on pyrolysis time and washing. The result is important as it suggested that adsorptive properties may change once biochars are exposed to the natural environment.

Technical Abstract: Biochars have been considered for adsorption of contaminants in soil and water, as well as conditioning and improving soil quality. One important property of the biochar is surface area in the pores of the biochar. Biochars were created from almond shells from two almond varieties with different ash content in the shells. The pyrolysis was performed in an inert nitrogen atmosphere at 650 and 800°C for 40 to 240 min. Characterization of the biochars showed that significant surface area (based on nitrogen adsorption isotherms) developed at the higher temperature and at pyrolysis times of 120 min and longer. Washing the materials in synthetic rainwater removed inorganic ash and exposed additional surface area, particularly in small-diameter pores. When results from low-ash almond shell biochars were compared with high-ash almond shell biochars, it was found that the pore distribution was more uniform for the high-ash starting material and almost independent of pyrolysis time or washing. The biochars from the low-ash starting material (Padre almond variety) showed a much greater dependence on pyrolysis time and washing. The result is important as it suggested that adsorptive properties may change once biochars are exposed to the natural environment.

Last Modified: 9/10/2014
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