Elevated soil lead (Pb) concentrations are a global concern owing to the toxic effects of this heavy metal. Solidification/stabilization (S/S) of soils using reagents like Portland cement (PC) is a common approach for the remediation of Pb contaminated sites. However, it has been reported that under long-term field conditions, the performance of PC treatments can diminish significantly. Therefore, novel reagents that provide longer-term stabilization performance are needed. In this study, four magnesium oxide (MgO) products of different reactivity values were applied (5 wt%) to a Pb contaminated clayey soil. The short-term (1-49 days) and long-term (25-100 years) temporal stabilization effects were investigated by laboratory incubation and accelerated ageing methods, respectively. The concentration of Pb in Toxicity Characterization Leaching Procure (TCLP) leachate was ~14 mg/L for the untreated soil; ~1.8 times higher than the TCLP regulatory level (5 mg/L). Only one day after treatment with MgO, the leachate concentration was reduced to below the regulatory level (a reduction of 69.4%-83.2%), regardless of the MgO type applied. However, in the long-term accelerated ageing experiments, only treatments using the most reactive MgO type could provide leachate concentrations that were consistently below the TCLP threshold throughout the 100 years of simulated ageing. The soil treated with the MgO of lowest reactivity was the first to exceed the regulatory level, at simulated year 75. It is thus demonstrated that MgO reactivity has a significant effect on its long-term effectiveness for contaminated soil stabilization. This is attributed to differences in their specific surface area and readiness to carbonate, which may facilitate the immobilization of Pb in the long term. It is also noteworthy that compared to PC, reactive MgO is more environmentally friendly owing to lower energy consumption and reduced CO2 emissions during its manufacture.

中文翻译：

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MgO反应性对铅污染土壤稳定的时间效应。

由于这种重金属的毒性作用，土壤铅（Pb）浓度升高成为全球关注的问题。使用诸如波特兰水泥（PC）之类的试剂对土壤进行固化/稳定化（S / S）是修复Pb污染部位的常用方法。但是，据报道，在长期的野外条件下，PC处理的性能可能会大大降低。因此，需要提供长期稳定性能的新型试剂。在这项研究中，将四种具有不同反应性值的氧化镁（MgO）产物（5 wt％）应用于受Pb污染的黏土。通过实验室培养和加速老化方法分别研究了短期（1-49天）和长期（25-100年）的时间稳定作用。对于未经处理的土壤，毒性表征浸出液（TCLP）沥出液中的铅浓度约为14 mg / L。比TCLP法规水平（5 mg / L）高约1.8倍。用MgO处理后仅一天，无论所用的MgO类型如何，渗滤液的浓度均降至低于规定水平（降低了69.4％-83.2％）。但是，在长期加速老化实验中，只有使用反应性最强的MgO类型的处理，才能提供在整个模拟老化的100年中始终低于TCLP阈值的渗滤液浓度。在模拟的第75年，用反应性最低的MgO处理的土壤首次超过了规定水平。因此证明，MgO的反应性对其污染土壤稳定的长期有效性具有重大影响。这归因于它们的比表面积和对碳酸盐的准备程度的差异，从长远来看，这可能有助于铅的固定化。还值得注意的是，与PC相比，反应性MgO在制造过程中具有更低的能耗和更低的CO2排放量，因此对环境更加友好。