Abstract

Rare earth elements (REEs) are currently used in fertilizers, but their behavior in the soil–plant system remains poorly understood. The assessment of the binding of REEs to various organomineral phases of soils remains an important task. Using soddy-podzolic soil and typical chernozem as examples, we performed a comparative study of two procedures of the fractionation of REEs in soils in the dynamic extraction mode. According to a five-stage procedure using a 0.05 M Ca(NO₃)₂ solution, 0.43 M CH₃COOH, a 0.1 M NH₂OH⋅HCl solution (pH 3.6), a 0.1 M K₄P₂O₇ solution (pH 11.0), and a 0.1 M (NH₄)₂C₂O₄ solution (pH 3.2), five extractable fractions were isolated, which can be conventionally named, exchangeable, specifically sorbed, associated with manganese oxides, associated with organic matter, and associated with amorphous and weakly crystallized oxides of iron and aluminum, respectively. A four-stage procedure, using a 0.05 M Ca(NO₃)₂ solution, a 0.1 M citric acid solution, a 0.05 M NH₂OH⋅HCl solution (pH 2.0), and 1.4 M HNO₃, enabled the isolation of exchange ions and fractions bound to carbonates, reducible, and acid-soluble, respectively. The concentration of elements in the initial samples and extracts was determined by atomic emission spectrometry and inductively coupled plasma mass spectrometry. In a five-stage procedure, the main extractable REE species (up to 40% of the total content) is provided by organometallic complexes extracted with a 0.1 M solution of potassium pyrophosphate. Using a four-stage procedure, the main fraction of REEs (up to 30%) is extracted with 1.4 M nitric acid. Using La, Ce, and Nd as examples, two procedures were compared. The concentration of REEs extracted by nitric acid (four-stage procedure) corresponds to the concentration of REEs extracted by pyrophosphate (five-stage procedure). In addition, the use of a 0.05 M NH₂OH⋅HCl solution at pH 2.0 (four-stage procedure) and a 0.1 M (NH₄)₂C₂O₄ solution at pH 3.2 (five-stage procedure) leads to similar results. Thus, both procedures can be used for the dynamic fractionation of REE species in soils. However, the five-stage procedure is preferable, because the reagents used are sufficiently selective with respect to the dissolved organomineral phases of soils, which more clearly reflects the pattern of the distribution of REE species.

中文翻译：

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土壤中稀土元素动态分馏方法的比较研究

摘要

稀土元素 (REE) 目前用于肥料，但它们在土壤 - 植物系统中的行为仍知之甚少。评估 REE 与土壤各种有机矿物相的结合仍然是一项重要任务。以黄腐土和典型黑钙土为例，对两种土壤中稀土元素在动态提取模式下的分馏工艺进行了对比研究。根据使用 0.05 M Ca(NO ₃ ) ₂溶液、0.43 M CH ₃ COOH、0.1 M NH ₂ OH·HCl 溶液 (pH 3.6)、0.1 MK ₄ P ₂ O ₇溶液 (pH 11.0) 和 0.1 M (NH ₄ ) ₂ C ₂O ₄溶液（pH 3.2），分离出五种可萃取的馏分，它们分别可以按惯例命名、可交换、具体吸附、与锰氧化物相关、与有机物相关、以及与铁和铝的无定形和弱结晶氧化物相关。一个四阶段程序，使用 0.05 M Ca(NO ₃ ) ₂溶液、0.1 M 柠檬酸溶液、0.05 M NH ₂ OH⋅HCl 溶液 (pH 2.0) 和 1.4 M HNO ₃，能够分离交换离子和分别与碳酸盐、可还原和酸溶性结合的馏分。通过原子发射光谱法和电感耦合等离子体质谱法测定初始样品和提取物中元素的浓度。在五步程序中，主要可提取的 REE 种类（最多占总含量的 40%）由用 0.1 M 焦磷酸钾溶液提取的有机金属配合物提供。使用四阶段程序，使用 1.4 M 硝酸提取主要部分的 REE（高达 30%）。以 La、Ce 和 Nd 为例，对两种程序进行了比较。硝酸提取的 REE 浓度（四步程序）对应于焦磷酸盐提取的 REE 浓度（五步程序）。此外，使用 0.05 M NHpH 2.0 的₂ OH·HCl 溶液（四阶段程序）和pH 3.2的 0.1 M (NH ₄ ) ₂ C ₂ O ₄溶液（五阶段程序）导致类似的结果。因此，这两种方法都可用于土壤中稀土元素的动态分馏。然而，五阶段程序是优选的，因为所使用的试剂对土壤中溶解的有机矿物相具有足够的选择性，这更清楚地反映了 REE 物种的分布模式。