Kinetics of trace metals sorption on and desorption from soils: Developing predictive models

Understanding the kinetics of trace metals sorption and desorption on soils is important for better prediction of metal behavior in the environment. In this dissertation, the effect of solution chemistry and soil composition on trace metal sorption and desorption kinetics was investigated. Based on the experimental results, predictive kinetics models were formulated and successfully used to describe the kinetics of trace metals sorption and desorption on a variety of soils.; The kinetics experiments were conducted with a stirred-flow method. A number of soil samples, which cover a wide range of soil properties from USA and European countries, were selected to test the effect of soil composition. The effects of solution chemistry, pH, metal loadings, and dissolved organic matter (DOM) concentration, were also systematically examined. Most of kinetics experiments were run with two trace metals, copper and zinc, which demonstrated very different kinetics behaviors. The solution pH has significant effect on the Cu and Zn sorption and desorption kinetics which can be accounted by the proton competition. DOM greatly enhanced Cu release but had little effect on Zn, attributed to formation of strong Cu-DOM complex decreasing the Cu ion re-adsorption on soils. Among all soil components, soil organic matter (SOM) is the dominant phase controlling Cu and Zn sorption and desorption kinetics. The effect of residence time was also tested.; The kinetics models were formulated and successfully used to describe the Cu and Zn sorption and desorption kinetics under different solution chemistry and soil compositions. The models are based on the mass balance of the flow system and incorporate the chemical reactions between metals and soils. For Zn, a two-site kinetics model, including one fast and one slow site, was necessary. The soil organic carbon (SOC) is the major model parameter accounting for the effect of soil properties on Zn sorption and desorption kinetics. The organic carbon normalized sorption rate coefficients can be applied to different soils based on their SOC concentrations. One set of rate coefficients can be applied to different influent Zn concentrations, which corresponds to the linear portion of the Zn sorption isotherm. The sorption rate coefficients were dependent on solution pH which was accounted for by Zn and proton competition. The same model parameters can be applied to different flow rates. (Abstract shortened by UMI.)...