土壤铁锰结核的环境地球化学行为研究进展

Environmental Geochemical Behavior of Soil Ferromanganese Nodules: A Review

  • 摘要: 铁锰结核(FMNs)是成土过程的次生产物,在岩溶地质高背景区广泛发育,是解释岩溶区土壤重金属“高总量、低生物有效性”现象的核心。然而,目前仍对其微观机制认识不足,结核动态形成演化及其环境行为的影响缺乏系统关联,以及对不同表生环境下结核地球化学行为的差异性与规律尚未作出清晰总结等问题。本文系统综述了土壤铁锰结核研究的最新进展,包括:①归纳了结核的形成机理、演化过程及其古环境指示意义:不同物理、化学以及生物因素共同控制结核的规律性生长,其中最核心的驱动因素是氧化还原电位。对比了不同表生环境下结核的地球化学特征,提出可能的影响路径模式;②总结了结核的生态效应以及对重金属的富集机制研究与实验技术:铁锰结核中Cd、Pb、Ni等元素含量可达对应土壤的数十倍,且pH浸出实验的最大释放量仅为17%(As)。通过扩展X射线吸收精细结构光谱(EXAFS)、X射线吸收近边结构光谱(XANES)、激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)等测试技术证实,结核通过表面络合、专性吸附及共沉淀等方式强力固定重金属。结核可以通过氧化或吸附影响砷、铬、磷等特征元素迁移转化。未来研究亟需建立基于环境参数的动态风险预警模型,加强多学科交叉融合,将结核的环境效应研究成果纳入土壤环境质量标准和风险管控实践中,实现土地资源的精细化管理和安全利用,为地质高背景区土壤风险精准评价与土地安全利用提供科学依据。

     

    Abstract: Ferromanganese nodules (FMNs), secondary products of pedogenic processes, are extensively distributed in karst regions characterized by high geochemical backgrounds and are central to explaining the apparent paradox of high total concentrations but low bioavailability of heavy metals in karst soils. However, there remains a limited understanding of their micro-scale mechanisms, a lack of systematic linkage between the dynamic formation and evolution of FMNs and their environmental behavior, and an absence of clear syntheses of the differences and governing patterns of FMNs geochemical behavior under varying supergene environments. This study presents a systematic review of recent advances in soil FMNs research. (1) The formation mechanisms, evolutionary pathways, and paleoenvironmental implications of FMNs are synthesized: physical, chemical, and biological factors collectively govern the systematic growth of FMNs, with redox potential serving as the fundamental driver. Based on a comparison of the geochemical characteristics of FMNs from different supergene environments, a model for their possible influence pathways is proposed accordingly. (2) The ecological impacts of FMNs,their enrichment mechanisms for heavy metals,and associated experimental methodologies are synthesized: FMNs exhibit enrichment factors of one to two orders of magnitude for Cd, Pb, Ni, and other trace elements relative to host soils, yet pH-dependent leaching experiments demonstrate maximum release rates of merely 17% (e.g., for As). The application of techniques such as EXAFS, XANES, and LA-ICP-MS confirms that FMNs strongly immobilize heavy metals through surface complexation, specific adsorption, and co-precipitation. FMNs can influence the mobilization and transformation processes of characteristic elements, such as arsenic, chromium, and phosphorus, through oxidation or adsorption. Future research priorities include: establishing dynamic risk assessment and early-warning models based on environmental parameters; enhancing cross-disciplinary integration; incorporating findings regarding FMNs environmental effects into soil quality standards and risk management protocols; facilitating precision land management and safe utilization practices; and furnishing scientific foundations for accurate soil risk assessment and sustainable land use in geochemical high-background regions. The BRIEF REPORT is available for this paper at http://www.ykcs.ac.cn/en/article/doi/10.15898/j.ykcs.202509140239.

     

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