Initial feasibility study in adsorption capacity and mechanism of soda residue on lead (Ⅱ)-contaminated soil in solidification/stabilization technology

摘要

Soil contaminated by potentially toxic trace elements (PTEs) may cause serious deteriorations to the environment and human health. With the aims of PTEs removal and resource reuse in solidification/stabilization technology, the soda residue was adopted as the adsorbent to mix with the soil in this study. The adsorption capacity of the mixture on Pb(II) was investigated by performing a series of adsorption tests with considerations of changes in soda residue content, pH value, initial Pb(II) concentration and temperature. While the adsorption mechanism was revealed by analyzing the adsorption isotherm models including Langmuir, Freundlich and Dubinin-Radushkevich models. Results showed that, the higher pH value, soda residue content and initial Pb concentration will improve the adsorption capacity of soda residue on Pb ions. In contrast, the enhanced temperature will reduce the corresponding adsorption capacity. The Langmuir adsorption isotherm model is much better than the Freundlich model at describing the adsorption behavior, indicating the monolayer adsorption with uniform distribution of active sites on the surface of mixture particle. The calculated maximum adsorption amount of the tested specimen is 34 mg/g, which is significantly higher than those of other clay materials, implying that soda residue has a notable potential for adsorption of Pb(II) at contaminated sites. Analysis using the Dubinin-Radushkevich adsorption isotherm model shows that the adsorption mechanism is strongly controlled by the chemical effects. The strong sensibility of adsorption capacity to environmental condition indicates that other cementitious materials should be explored and mixed with highly-content soda residue to enhance the durability of solidified/stabilized PTEs contaminated soil.