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Title: Mechanisms of antimony adsorption onto soybean stover-derived biochar in aqueous solutions

Author
item Vithanage, Meththika - Kangwon National University
item Rajapaksha, Anushka - Kangwon National University
item Ahmad, Mahtab - Kangwon National University
item Uchimiya, Sophie
item Dou, Xiaomin - Beijing Forestry University
item Alessi, Daniel - University Of Alberta
item Ok, Yong - Kangwon National University

Submitted to: Journal of Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2014
Publication Date: 11/6/2015
Citation: Vithanage, M., Rajapaksha, A.U., Ahmad, M., Uchimiya, M., Dou, X., Alessi, D.S., Ok, Y.S. 2014. Mechanisms of antimony adsorption onto soybean stover-derived biochar in aqueous solutions. Journal of Environmental Management. 151:443-449.

Interpretive Summary: Biochar is a solid co-product formed during the controlled heat treatment of agricultural wastes to produce bioenergy. Biochar property can be attenuated to remove a variety of target contaminants in soil and other aqueous environments. However, limited information is available to understand the underlying mechanism: how contaminant becomes incorporated onto biochar. This study systematically compared the effects of pH, electrolyte and other important solution components on the sorption of antimony onto biochars. Antimony contamination is often encountered at shooting range, roadsides, and mine sites. Unlike many other metals, antimony primarily forms negatively charged ions (anions) in water. Classical surface charge modeling was used to understand which antimony species most strongly sorbs on biochar. The results indicated that a few specifically and tightly bound antimony phases control the overall pollutant removal from water in the presence of biochar.

Technical Abstract: Limited mechanistic knowledge is available to understand how biochar interacts with trace elements that exist predominantly as oxoanions, such as antimony (Sb). Soybean stover biochars were produced at 300 degrees C (SBC300) and 700 degrees C (SBC700), and were characterized by BET, Boehm titration, FT-IR, NMR and Raman spectroscopy. Binding protons were determined by potentiometric titration and biochars were represented by two acidic sites for the surface complexation modeling. The zero point of charge was observed at pH 7.20 and 7.75 for SBC300 and SBC700, respectively. Neither antimonate (Sb(V)) nor antimonite (Sb(III)) showed ionic strength dependency (0.1, 0.01 and 0.001 M NaNO3), indicating inner sphere complexation. Greater adsorption of Sb(III) and Sb(V) was observed for SBC300 than SBC700, because of the higher content of -OH functional group. The % soluble Sb(III) removal was greater (85 %) than Sb(V) (68 %). Maximum adsorption density for Sb(III) was calculated as 1.88×10-6 mol m-2. Triple Layer Model (TLM) successfully described surface complexation of Sb onto soybean stover-derived biochar at pH 4-9, and suggested the formation of monodentate mononuclear and binuclear complexes. Spectroscopic investigations by Raman, FT-IR and XPS further confirmed strong binding of Sb to biochar surfaces.