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Title: Retention of heavy metals by carboxyl functional groups of biochars in small arms range soil

item Uchimiya, Sophie
item BANNON, DESMOND - United States Army Center For Health Promotion And Preventative Medicine
item Wartelle, Lynda

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2012
Publication Date: 1/26/2012
Citation: Uchimiya, M., Bannon, D.I., Wartelle, L.H. 2012. Retention of heavy metals by carboxyl functional groups of biochars in small arms range soil. Journal of Agricultural and Food Chemistry. 60(7):1798-1809.

Interpretive Summary: This study demonstrates how surface property of different biochars can be manipulated to enhance their ability to reduce water-soluble concentration and bioavailability of heavy metal contaminants. The results obtained in this study are applicable to cost-effective remediation of thousands of shooting ranges across the United States. The results suggested that biochars can be engineered to selectively remove target contaminants (Pb, Cu, and Zn) in field-obtained soil samples, without side-effects such as the release of other undesirable elements. The produced biochars have a potential for large-scale field application to remediate a wide range of soil types having problems related to heavy metals, and will at the same time allow end-user to reduce carbon footprint.

Technical Abstract: Long-term effectiveness of biochar for heavy metal stabilization depends upon biochar’s sorptive property and recalcitrance in soil. To understand the role of carboxyl functional groups on heavy metal stabilization, cottonseed hull biochar and flax shive steam activated biochar having low O/C ratio (0.04-0.06) and high fixed carbon content (˜80% dry weight basis) were oxidized using concentrated H2SO4/HNO3 and 30% HNO3. Oxidized and unoxidized biochars were characterized for O/C, total acidity, pH, moisture, ash, volatile matter, and fixed carbon contents, BET surface area, and ATR-FTIR spectral features. Characterized biochars were amended (2, 5, 10, and 20% in g biochar g-1 soil) on a sandy, slightly acidic (pH 6.27) heavy metal contaminated small arms range soil fraction (<250 'm) having low total organic carbon (0.518%) and low cation exchange capacity (0.95 meq/100 g). Oxidized biochars rich in carboxyl functional groups exhibited significantly greater Pb, Cu, and Zn stabilization ability compared to unoxidized biochars, especially in pH 4.9 acetate buffer (standard solution for toxicity characteristic leaching procedure), without causing the release of Sb. The results suggest that appropriate selection of biochar oxidant will produce recalcitrant biochars rich in carboxyl functional groups for long-term heavy metal stabilization strategy in contaminated soils.