Application of surface complexation modeling to trace metals uptake by biochar-amended agricultural soils

다국어 초록 (Multilingual Abstract)

<P><B>Abstract</B></P> <P>Biochar has emerged as a useful amendment to release nutrients into agricultural soil, to increase crop productivity, and as a sorbent to remediate metals and organics contamination. Since soils have heterogeneous physical properties across a given crop field, and even over a growing season, it is imperative to select the most appropriate biochar for the intended purpose and in defining the amendment level. In this study, we investigate the adsorption of Cd(II) and Se(VI) as model pollutant cations and anions, respectively, to two agricultural soils amended with a wood pin chip biochar (WPC). The proton reactivity of each sorbent was determined by potentiometric titration, and single-metal, single-sorbent experiments were conducted as a function of pH. The resulting data were modeled using a non-electrostatic surface complexation modeling (SCM) approach to determine the proton and metal binding constants and surface functional group concentrations of each soil and WPC. The SCM approach is a considerable advance over empirical modeling approaches because SCM models can account for changes in pH, ionic strength, temperature, and metal-to-sorbent ratio that may happen over the course of a growing season. The constants derived from the single-metal, single-sorbent experiments were then used to predict the extent of metal adsorption in more complex mixtures of Cd, Se, soil and WPC. Overall the SCM approach was successful in predicting metal distribution in multi-component mixtures. In cases where the predictions were poorer than expected, we identify reasons and discuss future experiments needed to further the application of SCM to sorbent mixtures containing biochar.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Cd(II) and Se(VI) adsorption to biochar, soils and their admixtures is tested as a function of pH. </LI> <LI> Surface complexation modeling is applied to biochar-amended soils for the first time. </LI> <LI> Potential impacts of metal-DOC complexes is explored. </LI> <LI> Cd(II) and Se(VI) adsorption to biochar-soil mixtures is generally well-predicted by models. </LI> <LI> Surface complexation models are a promising alternative to empirical adsorption models in the systems tested. </LI> </UL> </P>