Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 21, 2011
Publication Date: October 11, 2011
Citation: Ippolito, J.A., Strawn, D.G., Scheckel, K.G., Novak, J.M., Ahmedna, M., Niandou, M.S. 2011. Microscopic and molecular investigations of copper sorption by a stream activated biochar. Journal of Environmental Quality. 35(6):2333-2341 doi:10.2134/jeq2006.0075. Interpretive Summary: We examined the ability of biochar to sorb copper from solution. Biochar sorbed increasing amounts of copper as solution pH decreased. Copper appeared to be associated with biochar organic constituents under acidic pH, and copper was removed as different mineral phases under neutral to basic pH. We predicted that the maximum amount of copper biochar could sorb was 42,300 mg/kg copper. The results showed biochar may be utilized to sorb excess copper from water systems, potentially reducing the negative effects of copper in the environment.
Technical Abstract: Excessive copper concentrations in water systems can negatively impact biological systems. Because copper can form strong associations with organic functional groups, we examined the ability of biochar (a carbon-enriched organic bioenergy by-product) to sorb copper from solution. In a batch experiment, potassium hydroxide-steam activated pecan shell biochar was shaken for 24 hours in pH 6, 7, 8, or 9 buffered solutions containing various copper concentrations to identify effect of pH on biochar copper sorption. Afterwards, all biochar solids from the 24 hours shaking period were air-dried and then analyzed using X-ray absorption fine structure spectroscopy to determine solid-phase copper speciation. In a separate batch experiment, biochar was shaken for 30 days in pH 6 buffered solution containing increasing copper concentrations; the copper sorption maximum was calculated based on the exponential rise to a maximum equation. Biochar sorbed increasing amounts of copper as the solution pH decreased from 9 to 6. The X-ray absorption fine structure results revealed that copper was predominantly sorbed onto a biochar organic phase at pH 6 in a molecular structure similar to copper adsorbed on humic acid. The X-ray absorption fine structure spectra at pH 7, 8, and 9 suggested that copper was associated with the biochar as three phases: 1) a complex adsorbed on organic ligands similar to copper on humic acid; 2) carbonate phases similar to azurite; and 3) a copper oxide phase like tenorite. The exponential rise equation fit to the incubated samples predicted a copper sorption maximum of 42,300 mg/kg copper. The results showed that potassium hydroxide-steam activated pecan shell biochar could be utilized as a material for sorbing excess copper from water systems, potentially reducing the negative effects of copper in the environment.