Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/26/2010
Publication Date: 2/9/2011
Citation: Uchimiya, M., Klasson, K.T., Wartelle, L.H., Lima, I.M. 2011. Influence of soil properties on heavy metal sequestration by biochar amendment: 1. copper sorption isotherms and the release of cations. Chemosphere. 82(10):1431-1437.
Interpretive Summary: Agricultural wastes such as nutshells and manures can be thermochemically converted to biochars and activated carbons that can be placed back in soils to economically enhance crop yields and to clean up contaminated sites. For different soil types and the purpose of application, biochars and activated carbons should be carefully selected for use in this sustainable agricultural recycling process. In this study, nutshell-derived activated carbon and manure-derived biochar were tested for their ability to sequester toxic heavy metal copper in two different soil types. The amendment of biochar and activated carbon was more effective for sequestering copper in a soil that was unable to retain copper on its own. The results obtained in this study will facilitate the selection and application of thermochemically converted agricultural wastes for environmental remediation, based on fundamental interaction mechanisms.
Technical Abstract: The amendment of carbonaceous materials such as biochars and activated carbons is a promising in situ remediation strategy for both organic and inorganic contaminants in soils and sediments. Mechanistic understandings in sorption of heavy metals on amended soil are necessary for appropriate selection and application of carbonaceous materials for heavy metal sequestration in specific soil types. In this study, copper sorption isotherms were obtained for soils having distinct characteristics: clay-rich, alkaline San Joaquin soil with significant heavy metal sorption capacity, and eroded, acidic Norfolk sandy loam soil having low capacity to retain copper. The amendment of acidic pecan shell-derived activated carbon and basic broiler litter biochar lead to a greater enhancement of copper sorption in Norfolk soil than in San Joaquin soil. In Norfolk soil, the amendment of acidic activated carbon enhanced copper sorption primarily via cation exchange mechanism, i.e., release of proton, calcium, and aluminum, while acid dissolution of aluminum cannot be ruled out. For San Joaquin soil, enhanced copper retention by biochar amendment likely resulted from the following additional mechanisms: electrostatic interactions between copper and negatively charged soil and biochar surfaces, sorption on mineral (ash) components, complexation of copper by surface functional groups and delocalized Pi electrons of carbonaceous materials, and precipitation. Influence of biochar on the release of additional elements (e.g., Al, Ca) must be carefully considered when used as a soil amendment to sequester heavy metals.