Faculty of Eng., Bu-Ali Sina University, Hamedan, Iran; School of Civil Engineering, University of Tehran, Iran.
William Scott Professor Emeritus, McGill University, Montreal, Canada.
J Hazard Mater. 2021 Feb 5;403:123969. doi: 10.1016/j.jhazmat.2020.123969. Epub 2020 Sep 16.
The cement-based solidification/stabilization is commonly used to remediate heavy-metal-contaminated clayey soils. The major problem associated with this method is heavy-metal precipitation, which retards cement hydration. The objectives of this paper are to study the influence of pH-dependent lead solubility patterns on the solidification/stabilization of contaminated smectite and to overcome the problems associated with cement hydration in this process through NaOH treatment. A series of physicochemical experiments were performed on untreated and NaOH-enhanced samples. Contaminated smectite with 5-100 cmol/kg-soil of lead nitrate was solidified/stabilized by 10-50% cement. This research demonstrates that solidification/stabilization is a pH-dependent phenomenon. Enhancement increases the pH of contaminated soil in which lead components transfer to a soluble form. Hereafter, as the results of XRD reveal, a decrease in lead precipitation on cement components is observed. Consequently, a noticeable increase in CSH formation is detected. The capsulation of lead ions by CSH improves the setting-time and unconfined compressive strength of solidified/stabilized samples. Furthermore, the TCLP results show a significant reduction in samples' lead-leaching abilities. Therefore, enhancement has changed the governing retention phenomena from precipitation/stabilization in lead carbonate form to mainly capsulation/solidification by CSH. Moreover, the results show a noticeable reduction in the required cement content.
基于水泥的固化/稳定化技术常用于修复重金属污染的粘性土壤。该方法的主要问题是重金属沉淀，这会阻碍水泥水化。本文的目的是研究 pH 依赖性铅溶解度模式对受污染蒙脱石的固化/稳定化的影响，并通过 NaOH 处理克服该过程中水泥水化的相关问题。对未经处理和经 NaOH 增强的样品进行了一系列物理化学实验。用 10-50%的水泥固化/稳定化土壤中含有 5-100 cmol/kg 的硝酸铅的受污染蒙脱石。研究表明，固化/稳定化是一个 pH 依赖性的现象。增强会提高受污染土壤的 pH 值，使铅成分转化为可溶形式。此后，正如 XRD 结果所示，水泥成分上的铅沉淀减少。因此，检测到 CSH 的形成明显增加。CSH 对铅离子的封端提高了固化/稳定化样品的凝结时间和无侧限抗压强度。此外，TCLP 结果表明，样品的铅浸出能力显著降低。因此，增强改变了主要的保留现象，从铅碳酸形式的沉淀/稳定化转变为主要的 CSH 封端/固化。此外，结果表明所需的水泥含量显著减少。
