Extraction of aluminium and iron from organic associations in soil - developing a new selective method

从土壤中的有机组合物中提取铝和铁 - 开发新的选择性方法

• 批准号: 519407628
• 负责人: Professor Dr. Thilo Rennert
• 金额: --
• 依托单位: Fachgebiet Bodenchemie mit Pedologie (310a)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/519407628?language=en
• 关键词: Extraction; aluminium; iron; organic; associations

Metal ions such as Al3+ and Fe2+/3+ are released during soil development, and they may react with soil organic matter (SOM). Interactions between metal cations and SOM are known for decades, inducing SOM stabilization, that is, the deceleration of SOM decomposition. In acidic soil, these interactions comprise adsorption of Al and Fe ions on functional groups of SOM, and co-precipitation of the ions with SOM, resulting in organic associations of the metals. Oxalate dissolves metals in organic association, together with metals in mineral forms. Recent studies have shown that particularly the contents of oxalate-extractable Al are one of the predictors of the contents of soil organic carbon. Despite the importance of metals in organic association, there is no method for their selective extraction available. The proposed project aims to develop a scheme for the complete and selective extraction of Al and Fe in organic association and for the quantitative and qualitative characterization of the SOM associated with Al. A fluoride-based extraction (pH 6.5) will be developed and integrated into a sequential extraction scheme for this purpose. The scheme will separately extract Al and Fe from organic associations, poorly crystalline Fe oxides, and short-range ordered aluminosilicates. Selectivity and completeness of the fluoride-based extraction will be tested with models of organic associations and reference minerals before transferring the method to soils. Then, soil samples, in which enhanced contents of Al and Fe in organic association are expected, will be extracted according to the scheme. The samples will originate from horizons of reference soil groups of the WRB classification, into which metal-organic associations have been transported (Podzols, Luvisols), in which the associations have formed in situ (Andosols, Cambisols), and in which they have formed because of redox processes (Gleysols, Stagnosols). Depending on the pedogenic milieu, variable contents of metals and SOM in organic association are expected, together with variable contributions of metals in organic association to the contents of oxalate-extractable metals as a sum parameter. SOM extracted from associations with Al will be characterized with spectroscopic methods and a thermal one. These results are expected to differ as well, depending on the pedogenic milieu, for instance, larger proportions of low-molecular-mass organic acids in Podzols compared to Andosols with more aromatic SOM. The project is not only for the development and for the application of a selective extraction of Al and Fe in organic association in soil, but also for the characterization of a SOM fraction, which was not selectively accessible yet. Thus, apart from advancing soil-chemical analytics, the project will provide fundamental pedogenetic data that may be implemented into models on the controls of organic-carbon storage in soil, if larger sample sets will be studied.

土壤发育过程中会释放出Al3+、Fe2+/3+等金属离子，并与土壤有机质（SOM）发生反应。金属阳离子与SOM之间的相互作用已经知道了几十年，导致SOM稳定，即SOM分解的减速。在酸性土壤中，这些相互作用包括Al和Fe离子在SOM官能团上的吸附，以及这些离子与SOM的共沉淀，从而导致金属的有机结合。草酸盐能溶解有机结合的金属和矿物形式的金属。近年来的研究表明，特别是草酸可提取铝的含量是土壤有机碳含量的预测指标之一。尽管金属在有机结合中的重要性，但目前还没有选择性提取金属的方法。拟议的项目旨在制定一项方案，以便在有机结合中完整和选择性地提取Al和Fe，并对与Al相关的SOM进行定量和定性表征。为此目的，将开发一种基于氟化物的提取方法（pH为6.5），并将其纳入顺序提取方案。该方案将分别从有机结合物、低结晶铁氧化物和短程有序铝硅酸盐中提取Al和Fe。在将该方法转移到土壤之前，将用有机结合物和参考矿物模型测试氟基提取的选择性和完整性。然后，根据该方案提取有机结合中Al和Fe含量有望提高的土壤样品。样品将来自WRB分类的参考土壤群的层位，其中金属-有机结合已被输送到其中（Podzols, Luvisols），其中金属-有机结合已在原地形成（Andosols, Cambisols），并且由于氧化还原过程而形成（Gleysols, Stagnosols）。根据成土环境的不同，预计有机结合体中金属和SOM的含量是可变的，有机结合体中金属对草酸盐可提取金属含量的贡献也是可变的。从与Al结合物中提取的SOM将用光谱方法和热方法进行表征。这些结果预计也会有所不同，这取决于成土环境，例如，与含有更多芳香族SOM的安土相比，灰土中低分子质量有机酸的比例更大。该项目不仅是为了开发和应用土壤中有机结合物中Al和Fe的选择性提取，而且是为了表征尚未选择性获得的SOM分数。因此，除了推进土壤化学分析之外，该项目还将提供基本的成土数据，如果研究更大的样本集，这些数据可能会被应用到土壤有机碳储存控制模型中。