Selective dissolution of magnetic iron oxides in the acid-ammonium oxalate/ferrous iron extraction method-I. Synthetic samples
Selective dissolution of magnetic iron oxides in the acid-ammonium oxalate/ferrous iron extraction method-I. Synthetic samples
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酸性草酸铵/亚铁提取法选择性溶解磁性氧化铁-I．
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发表时间：
2001
期刊：
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通讯作者：
M. Dekkers
中科院分区：
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作者：
I. V. Oorschot;M. Dekkers
摘要在土壤磁性中，单独的磁性参数并不总是足以区分成岩磁性组分和成壤磁性组分。因此，顺序提取技术已被纳入磁性研究，以限制环境的解释。在这里，我们报告了酸性草酸铵法中磁铁矿和磁赤铁矿的溶解行为，以确定该方法是否适用于土壤和沉积物中磁性矿物的特定溶解。为了防止实验期间浸提机制发生变化（见附录A），我们使用了改良版的草酸铵（AAO）法，其中在实验前将Fe 2+加入浸提溶液中[AAO-Fe（II）法]。将该程序分为几个30 min浸提步骤，以检查溶出进度。用AAO-Fe（II）方法提取了含有0.1%（重量）氧化铁的石英基质的合成样品。氧化铁由粒度<0.5 mm（细粒或SD/PSD）和<5 mm（粗粒或MD/PSD）的磁铁矿或磁赤铁矿组成，或由两种矿物的1：1混合物组成。因为只有磁铁矿和磁赤铁矿进行了研究，磁特性的变化可以监测后，每个提取步骤的体积磁化率和磁滞参数在室温下测量的分析。AAO-Fe（II）法优先溶解样品中较小的铁氧化物。对于含有粗粒度氧化铁的样品，磁赤铁矿比磁铁矿更易溶解。含有两种不同粒度或不同矿物学的混合物的样品的提取表明，该方法优先溶解较小的颗粒，然后攻击样品中的粗颗粒。
SUMMARY In soil magnetism, the magnetic parameters alone are not always sufficient to distinguish the lithogenic from the pedogenic magnetic fractions. Sequential extraction techniques have therefore been incorporated into magnetic studies to constrain the environmental interpretation. Here we report on the dissolution behaviour of magnetite and maghemite in the acid‐ammonium oxalate method to see whether the method is suitable for specific dissolution of magnetic minerals from soils and sediments. To prevent changes in the extraction mechanism during the experiments (see Appendix A), we used an adapted version of the acid‐ammonium oxalate (AAO) method, in which Fe 2+ is added to the extraction solution prior to the experiment [the AAO-Fe(II) method]. The procedure was divided into several 30 min extraction steps to check the dissolution progress. Synthetic samples containing a quartz matrix with 0.1 wt per cent of iron oxides were extracted with the AAO-Fe(II) method. The iron oxides consisted of either magnetite or maghemite with grain sizes of <0.5 mm (fine grained or SD/PSD) and <5 mm (coarse grained or MD/PSD), or a 1 : 1 mixture of both minerals. Because only magnetite and maghemite were studied, the changes in magnetic characteristics could be monitored after each extraction step by analysis of the bulk susceptibility and hysteresis parameters measured at room temperature. The AAO-Fe(II) method preferentially dissolved the smaller iron oxides from the samples. For samples containing iron oxides with coarse grain size there is a preference for dissolving maghemite rather than magnetite. Extractions of the samples containing mixtures of two different grain sizes or with different mineralogy show that the method preferentially dissolves the smaller grains before attacking the coarse grains in the sample.