可迁移性零价铁的制备及其活化过硫酸盐氧化修复石油污染土壤
Preparations of mobile PASP-S-zero-valent iron materials for the persulfate-based remediation of petroleum-contaminated soils
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摘要: 纳米零价铁(nZVI)活化过硫酸盐(PS)体系具有活性高、持效性长等潜在优势,在有机污染土壤修复领域具有良好的应用前景。然而,nZVI颗粒易于发生团聚和氧化作用,在土壤中迁移性能和稳定性能较差,限制了其活化性能的发挥。该研究采用聚天冬氨酸(PASP)修饰和硫化改性技术,制备了复合改性的PASP-S-nZVI复合材料,评价了PASP-S-nZVI的活化PS性能、在石英砂填充介质中的迁移性能,优化了该材料活化PS降解土壤中石油烃的反应条件,并开展了土壤污染修复小试试验。表征结果显示,PASP-S-nZVI材料为表面具有PASP涂层及硫铁化物(FeSx)的零价铁。与未改性nZVI和S-nZVI相比,PASP-S-nZVI材料的悬浮稳定性、Zeta电位和电子利用率都显著增加,表明双重改性增加了nZVI的稳定性能。柱实验结果显示,PASP-S-nZVI具有低的附着效率,其实际碰撞效率是S-nZVI的38.0%、nZVI 的26.5%,在含水介质中的迁移性能显著增加,且增加程度与填充介质的粒径尺寸和水体pH有关。在优化的条件参数下,PASP-S-nZVI材料高效活化PS氧化降解土壤中石油烃,实验室实验中石油烃的3天的降解率为77±2%。土壤修复小试试验显示石油烃的3天的降解率达到53±2%,证实了PASP-S-nZVI材料在土壤中活化PS性能较好,具有潜在的应用前景。Abstract: Persulfates (PS) are a mainstream oxidant used for soil remediation contaminated by organic pollutants (petroleum hydrocarbons). Nano zero-valent iron (nZVI) is a well-known activator of persulfates, with the advantages of high catalytic reaction and long-term performance. However, nZVI readily undertakes agglomeration and oxidation processes in soils and thus displays poor stability and migration potential, both of which inhibit the activation potential of nZVI. In this study, we prepared PASP-S-nZVI composite materials by conducting combined modifications of nZVI with polyaspartic acid (PASP) and sodium hydrosulfite, and carried out quartz sand column experiments of PASP-S-nZVI and remediation experiments of petroleum-contaminated soils by PASP-S-nZVI/PS. Both SEM-SDS and XPS spectra of materials showed that the PASP-S-nZVI composite materials were characteristics of nZVI with both PASP coating layer and FeSx layer on the surface. The combined modifications resulted in reduction of total iron contents in composite materials but a notable increase in the stability of materials, due to both increases in zeta potential and specific surface area of materials. Both column experimental results and T-E model simulations showed that PASP-S-nZVI had higher mobility in the subsurface than nZVI and S-nZVI, due to notable reductions of actual single-collector removal efficiency of the composite materials by 73.5% and 62%, respectively. It was because PASP-S-nZVI had extremely low attachment efficiency, due to the PASP coating layer. The mobility of PASP-S-nZVI was dependent of particle sizes of porous medium and water pH in the subsurface. Under the optimized conditions, PASP-S-nZVI/PS efficiently removed petroleum hydrocarbons (TPHs) in soils, and the removal rate of TPHs (3 d) was 77±2% in the laboratory experiments. The pilot experiment also yielded a high removal rate of TPHs (3 d) by 53±2%, further indicating the performance of PASP-S-nZVI/PS in soils. This study indicates that PASP-S-nZVI with both improved mobility and catalytic reactivity may find its applications in soil remediation.
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