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岩溶地质高背景区土壤镉(Cd)富集机理研究现状

Research Status on the Mechanism of Cadmium Enrichment in the Soil of Karst Areas with High Geochemical Background

  • 摘要: 自然界中,碳酸盐岩为Cd等微量元素含量偏低的贫Cd成土母岩类型,但在岩溶出露区,土壤却普遍呈现Cd等微量元素富集的现象,具备典型的地质高背景特征,其中Cd来源不明,富集机理不清,引发了学术界的高度关注与系统研究。鉴于碳酸盐岩原位风化成土的广谱性,多数研究以此为切入点,结合两阶段风化成土、交代溶蚀成土、等容置换成土等理论,运用成土剖面、淋滤溶解实验、天然母质研究等手段,揭示原生继承与次生吸附综合作用下岩溶区Cd的迁移转化规律。岩溶区土壤相对于原岩普遍富集Cd等元素,但是富集效应在整个风化过程中并非是持续性的:①成土母质的形成与演化阶段为Cd富集的主要阶段,这一阶段Cd的富集主要归因于成土母质为土壤形成初期提供的高Cd来源以及磷灰石、黏土矿物、Fe-Mn氧化物对Cd的吸附;②成土过程是Cd的淋失过程,载体矿物的淋失和水解是Cd淋失的主要驱动力,由此引发的 Cd 活化也给岩溶地质高背景区带来了潜在的环境风险。目前,岩溶区风化成土过程中Cd迁移宏观规律的研究相对较为完善,但在研究方法和分析测试的层面仍可以进一步优化。本文建议研究过程尽量确保风化过程的连续性和完整性,在把握宏观规律的基础上,进一步深入揭示微观机制,为构建岩溶区土壤Cd富集的理论框架提供科学依据,同时也为岩溶地质高背景区土地资源的分类管理及生态环境的科学管护提供新的思路与方法。

     

    Abstract: In nature, carbonate rocks are a type of parent rock with relatively low concentrations of trace elements such as cadmium (Cd). However, in karst areas, soils with significantly enriched Cd are commonly found, exhibiting typical geological high background characteristics. The source of Cd in the soil is unknown, and the mechanism of its enrichment is unclear, which has attracted considerable attention and systematic research from the academic community. Considering the widespread in situ weathering of carbonate rocks into soil, most studies are based on this, combining theories such as two-stage weathering, metasomatic dissolution, and isovolumetric replacement. They use methods such as soil profiles, leaching and dissolution experiments, and natural parent material research to reveal the migration and transformation patterns of Cd in karst areas under the combined effects of primary inheritance and secondary adsorption. The Cd enrichment effect in karst soil is not continuous during weathering: (1) The formation and evolution of parent material is the main stage of Cd enrichment. During this stage, Cd enrichment is mainly attributed to the high Cd source provided by the parent material during the early stages of soil formation, as well as the adsorption of Cd by apatite, clay minerals, and Fe-Mn oxides. (2) During soil formation, Cd exhibits leaching behavior, and the leaching and hydrolysis of carrier minerals serve as the main driving forces for Cd leaching. The consequent activation of Cd also presents potential environmental risks to karst areas with high geological background. Currently, the macroscopic patterns of Cd migration during the weathering and pedogenesis process in karst regions are relatively well-established. However, the relevant research methods and analytical testing can still be further optimized. The suggestion is that research efforts should ensure the continuity and integrity of the weathering process. Based on an understanding of macro-level patterns, micro-level mechanisms should be further explored to provide a scientific basis for establishing a theoretical framework for Cd accumulation in karst soils. This research also aims to offer new approaches and methods for the management of land resources and the scientific conservation of the ecological environment in karst areas with high geological background.

     

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