School of Environment, Tsinghua University, Beijing 100084, China.
Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China.
J Hazard Mater. 2020 Apr 5;387:122005. doi: 10.1016/j.jhazmat.2019.122005. Epub 2020 Jan 2.
Solidification/Stabilization (S/S) is an effective way to immobilize toxic metals in contaminated soil. However, utilization of ordinary Portland cement (PC) in this process has raised environmental concerns owing to the high carbon footprint from PC manufacturing and the risk of toxic element leaching in the long term. Hence there is an urgent need to seek for "green" immobilization approaches with long-term stability. In this study, a clay-based material, humic acid modified montmorillonite (HA-Mont) was applied to a Cd and Hg contaminated soil. Field emission scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (FESEM/EDS), N adsorption-desorption, Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) analyses were performed to investigate the characteristics of this material. Compared to the soil without any treatment, dosage of 5 % HA-Mont could effectively reduce Cd and Hg concentrations by 94.1 % and 93.0 %, respectively and to below the regulatory limits in the TCLP (Toxicity Characteristic Leaching Procedure) leachates. Compared to the soil treated with virgin montmorillonite, HA modification resulted in the reduction of leachate concentrations of Cd and Hg by 69.5 % and 65.9 %, respectively. Long-term immobilization performance of the HA-Mont treatment was examined using a quantitative accelerated ageing method. In order to examine the ageing features, a novel method based on conditional probability was developed, and the reliability of HA-Mont immobilization was found to fit the Weibull model well, as the ageing rate of immobilization effect increased with time. After 120 years of ageing, reliability of both metals could still remain above 0.95. Cd concentration in TCLP leachates at 120 year could still remain below the regulatory limit (294 μg/L vs 1000 μg/L), while Hg concentration reached the regulatory limit of 200 μg/L in 96 year. This is the first attempt developing a green S/S method of Cd and Hg contaminated soil using HA-Mont and examining the long-term ageing characteristics of the stabilized soil using a probability-based approach.
固化/稳定化（S/S）是一种将有毒金属固定在污染土壤中的有效方法。然而，由于普通波特兰水泥（PC）制造过程中的高碳足迹以及长期存在的有毒元素浸出风险，该过程中使用普通波特兰水泥引起了环境方面的关注。因此，迫切需要寻求具有长期稳定性的“绿色”固定化方法。在这项研究中，一种基于粘土的材料，腐殖酸改性蒙脱石（HA-Mont）被应用于 Cd 和 Hg 污染土壤。通过场发射扫描电子显微镜结合能量色散 X 射线光谱（FESEM/EDS）、N 吸附-解吸、傅里叶变换红外（FTIR）光谱和 X 射线衍射（XRD）分析对该材料的特性进行了研究。与未经任何处理的土壤相比，添加 5%的 HA-Mont 可分别有效降低 Cd 和 Hg 的浓度 94.1%和 93.0%，并使其低于 TCLP（毒性特征浸出程序）浸出液中的规定限值。与用原蒙脱石处理的土壤相比，HA 改性可使 Cd 和 Hg 的浸出浓度分别降低 69.5%和 65.9%。采用定量加速老化法研究了 HA-Mont 处理的长期固定化性能。为了研究老化特征，开发了一种基于条件概率的新方法，发现 HA-Mont 固定化的可靠性非常适合威布尔模型，因为固定化效果的老化速率随时间的增加而增加。经过 120 年的老化，两种金属的可靠性仍能保持在 0.95 以上。120 年时 TCLP 浸出液中 Cd 的浓度仍低于规定限值（294μg/L 对 1000μg/L），而 Hg 的浓度在 96 年内达到了 200μg/L 的规定限值。这是首次尝试使用 HA-Mont 开发一种绿色的 Cd 和 Hg 污染土壤的 S/S 方法，并使用基于概率的方法研究稳定化土壤的长期老化特征。
