The impact of vegetation on the transport of heavy metals from contaminated soils.

摘要

Surface disposal of heavy metal contaminated mining, milling and metal processing wastes have negatively impacted the environment. To reduce the spread of heavy metal contamination by water and wind erosion, it is recommended that exposed contaminated soil be vegetated. Vegetation would provide cover to prevent erosion and reduce leaching events by decreasing soil moisture levels. The overall impact of vegetation on heavy metals is not fully understood In this study, the impact of vegetation on the transport of heavy metals will be assessed. Individual components of the experiment include; characterization of two heavy metal contaminated soils, modeling of the effect that organic acids have on heavy metals in contaminated soil, batch studies of interactions between organic acids and heavy metal contaminated soils, an adsorption study examining the effect organic acids have on the adsorption rate of heavy metals onto a soil, an unvegetated column study examining the leaching of heavy metals under the influence of organic acids and a vegetated column study.; Results from the characterization study and the modeling study were verified by the batch equilibrium study and the unvegetated column study. The type and binding strength of the heavy metals was determined by the characterization study. The mobilization of heavy metals organic acids was determined by the type of heavy metal and its binding to the soil matrix. The adsorption of heavy metals was affected by the presence of organic acids. In the case of oxalic acid, adsorption of heavy metals increased and, in the case of citric acid, adsorption of heavy metals decreased. The vegetated column study used two heavy metal contaminated soils and two different vegetation types to study the effect vegetation had on the transport of heavy metal within contaminated soils. Correlations between plant development, soil water movement, and leaching of heavy metals were explored. Results are presented for barium, cadmium, lead, and zinc movement in dissolved and suspended form. The presence of vegetation limited the leaching of heavy metals by limiting the amount of soil moisture.