Validation of TOF-SIMS and FE-SEM/EDS Techniques Combined with Sorption and Desorption Experiments to Check Competitive and Individual Pb2+ and Cd2+ Association with Components of B Soil Horizons

Sorption and desorption experiments were performed by the batch method on the B horizons of five natural soils: Umbric Cambisol, Endoleptic Luvisol, Mollic Umbrisol, Dystric Umbrisol, and Dystric Fluvisol. Individual and competitive sorption and desorption capacity and hysteresis were determined. The results showed that Pb2+ was sorbed and retained in a greater quantity than Cd2+ and that the hysteresis of the first was greater than that of the second. The most influential characteristics of the sorption and retention of Pb2+ were pH, ECEC, Fe and Mn oxides and clay contents. For Cd2+ they were mainly pH and, to a lesser extent, Mn oxides and clay content. The combined use of TOF-SIMS, FE-SEM/EDS and sorption and desorption analyses was suitable for achieving a better understanding of the interaction between soil components and the two heavy metals. They show the preferential association of Pb2+ with vermiculite, chlorite, Fe and Mn oxides, and of Cd2+ with the same components, although to a much lesser extent and intensity. This was due to the latter’s higher mobility as it competed unfavourably with the Pb2+ sorption sites. TOF-SIMS and FE-SEM/EDS techniques confirmed the results of the sorption experiments, and also provided valuable information on whether the soil components (individually or in association) retain Cd2+ and / or Pb2+; this could help to propose effective measures for the remediation of contaminated soils.

本研究采用批量平衡法，针对5种天然土壤的B层开展吸附与解吸实验，供试土壤分别为腐殖质雏形土（Umbric Cambisol）、潜育淋溶土（Endoleptic Luvisol）、腐殖质暗瘠土（Mollic Umbrisol）、酸性暗瘠土（Dystric Umbrisol）以及酸性冲积土（Dystric Fluvisol）。实验测定了单一与竞争体系下的吸附解吸容量及滞后效应。结果表明，铅离子（Pb²+）的吸附固持量高于镉离子（Cd²+），且其滞后效应亦强于后者。影响Pb²+吸附与固持的关键土壤特征依次为pH值、有效阳离子交换量（ECEC）、铁锰氧化物含量与黏粒含量；而影响Cd²+的主要因素为pH值，其次为锰氧化物与黏粒含量。联合使用飞行时间二次离子质谱（TOF-SIMS）、场发射扫描电镜/能谱仪（FE-SEM/EDS）与吸附解吸分析，可更为深入地解析土壤组分与两种重金属间的相互作用机制。研究显示，Pb²+优先与蛭石、绿泥石、铁锰氧化物结合，而Cd²+虽也可与上述组分结合，但结合程度与强度均显著更低，这源于Cd²+的迁移性更强，且在吸附位点竞争中处于劣势。TOF-SIMS与FE-SEM/EDS技术不仅验证了吸附实验的结果，还可为明确土壤组分（单独或复合状态）对Cd²+和/或Pb²+的固持能力提供有效信息，可为受污染土壤的修复措施制定提供理论支撑。