Abstract:

Stabilization technology (solidification/stabilization technology) is currently one of the most widely used technologies for the soil remediation of polluted sites. However, heavy metal-contaminated sites are subject to prolonged impacts from complex external environmental factors (such as flooding and drying cycles and leaching) during subsequent utilization after stabilization restoration, which may further lead to alterations in the occurrence state of stabilized heavy metals and their gradual release, posing environmental risks. In this study, typical stabilization remediated soil (SRS) in the Pearl River Delta region was collected, and experiments were designed and conducted to investigate the stability and influencing factors of two heavy metals (Ni and Pb) under simulated flooding and alternating dry-wet conditions. The results revealed that flooding treatments significantly increased the leaching concentrations of heavy metals in SRS. Specifically, the amount of leached Ni after flooding increased 103 times, whereas the effect of flooding on Pb was relatively insignificant. Flooding promotes the transformation of stabilized heavy metals from easily migratable weakly acid-extractable fractions to more stable oxidizable and reducible fractions. After flooding, the weakly acidic-extractable fractions of Ni and Pb decreased by 7.16% and 19.9%, respectively. Flooding affects the stability of heavy metals in SRS by altering the soil pH, E_h, iron-manganese oxides, and DOM. Specifically, the pH and E_h of the soil during flooding decreased, further leading to the reduction of Mn⁴⁺ and Fe³⁺ in the system and the re-release of heavy metals, coupled with a decrease in the content of amorphous iron oxides. In contrast, dry-wet alternation affects the stability of heavy metals by influencing the dissolution and desorption behavior of hydrolyzed heavy metal compounds. Overall, the effect of dry-wet alternation on the leaching concentration and morphological changes of Ni and Pb in the system were relatively insignificant. Taken together, flooding and dry-wet alternation stresses can alter the stability of heavy metals in the SRS, with the degree of change varying significantly depending on the type of heavy metal and the intensity of external stresses. The leaching concentrations of heavy metals in SRS after simulated stress in this study remained significantly below the relevant standard limits, indicating that the environmental risk of SRS is manageable in the short term. Nevertheless, given the long-term and diverse effects of external environmental factors, effectively extending the supervision chain and conducting regular retrospective evaluations of restored land plots are crucial for achieving the sustainable and safe utilization of contaminated sites.

Key words: flooding, dry-wet alternation, stabilization, heavy metals, environmental impact

摘要：

稳定化（固化/稳定化）技术被广泛应用于污染土壤的修复治理，但修复后的重金属会在外界复杂环境因子（淹水-落干、淋溶等）影响下改变赋存状态、缓慢释放，进而引发环境风险。选取珠三角地区典型稳定化修复后土壤为对象，研究模拟淹水、干湿交替两种情形下修复后土壤中2种重金属（Ni和Pb）的稳定性及其影响因素。结果表明，淹水可明显提高稳定化修复后土壤重金属的浸出浓度，淹水后Ni的浸出量较淹水前上升约103倍，重金属Pb浸出浓度受到淹水影响较小。淹水可促使稳定化的重金属从弱酸提取态向可氧化态和可还原态转化，淹水后Ni和Pb的弱酸提取态含量降幅分别为7.16%和19.9%。淹水通过改变土壤pH、E_h、铁锰氧化物和DOM等影响修复后重金属的稳定性，通过降低土壤pH和E_h促使体系中Mn⁴⁺、Fe³⁺还原，并同时耦合无定形态氧化铁的降低。干湿交替通过对水解重金属化合物的溶解解吸行为而影响重金属的稳定性，总体上干湿交替对体系中的Ni和Pb的浸出浓度、形态变化的影响相对较小。研究表明，淹水和干湿交替胁迫可以改变稳定化修复后土壤重金属的稳定性，且程度因不同重金属种类及外界胁迫强度而差异较大，短期内重金属浸出浓度远低于相关标准限值，土壤环境风险可控，但鉴于外界环境影响的长期性和多元性，实质性延长监管链条、对修复后地块实施定期回顾性评估是实现污染地块可持续安全利用的有效方式。

关键词: 淹水, 干湿交替, 稳定化, 重金属, 环境影响