Influence of soil properties on heavy metal sequestration by biochar amendment: 2. copper desorption isotherms

Authors: Uchimiya, Sophie; Klasson, K Thomas; Wartelle, Lynda; Lima, Isabel

Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/29/2010
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: 2. copper desorption isotherms. Chemosphere. 82(10):1438-1447.

Interpretive Summary: Desorption of contaminants must be carefully examined in order to predict the long-term effectiveness of an environmental remediation technology and bioavailability of contaminants. In this study, experiments were designed to simulate heavy metal contaminant (copper) desorption by rainfall events and to address toxicity characteristics. The results indicate that copper stays bound in soils amended with biochars and activated carbons during rainfall events, but extensively leaches out when the equilibrium established in rainwater is perturbed. Copper leaching was significantly diminished in the presence of acidic activated carbon. In addition to soil type and pH, the release of nutrients (e.g., P, K, Ca) and undesirable elements (e.g., Al, Zn) affected the sorption and desorption behaviors of copper.

Technical Abstract: Contaminant desorption constrains the long-term effectiveness of remediation technologies, and is strongly influenced by dynamic non-equilibrium states of environmental and biological media. Information is currently lacking in the influence of biochar and activated carbon amendments on desorption of heavy metal contaminants from soil components. In this study, copper sorption-desorption isotherms were obtained for 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. Acidic pecan shell-derived activated carbon and basic broiler litter biochar were employed in desorption experiments designed to address both leaching by rainfall and toxicity characteristics. For desorption in synthetic rain water, broiler litter biochar amendment diminished sorption-desorption hysteresis. In acetate buffer (pH 4.9), significant copper leaching was observed, unless acidic activated carbon (pHpzc = 3.07) was present. Trends observed in soluble phosphorus and zinc concentrations for sorption and desorption equilibria suggested acid-dissolution of particulate phases that can result in a concurrent release of copper and other sorbed elements. In contrast, sulfur and potassium became depleted as a result of supernatant replacements only when amended carbon (broiler litter biochar) or soil (San Joaquin) contained appreciable amounts. A positive correlation was observed between the equilibrium aluminum concentration and initial copper concentration in soils amended with acidic activated carbon but not basic biochar, suggesting the importance of cation exchange mechanism, while dissolution of aluminum oxides cannot be ruled out.