Selective dissolution of magnetic iron oxides in the acid-ammonium oxalate/ferrous iron extraction method-I. Synthetic samples

Abstract

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 Fe2+ 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 µm (fine grained or SD/PSD) and < 5 µm (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.

Novel hybrid nanostructured materials of magnetite nanoparticles and pectin

“…On the other hand, lower pH (e.g., pH $ 2) tends to reduce the zeta potential of pectin [6] and hence may not be suitable for chemical cross-linking with Ca 2 + ions. Besides, lower pH would favor dissolution of the MNPs encapsulated in the hybrid nanostructures of MCPs due to weakening of the Fe-O bond by protonation mechanism [31] and might lead towards loss of its magnetic property. As a compromise, pH $ 4 was chosen optimum for synthesis of MCPs which offered suitably high zeta potential of pectin (z ¼ À35.7 mV, Table 1).…”

Selective dissolution of magnetic iron oxides with the acid-ammonium-oxalate/ferrous-iron extraction technique-II. Natural loess and palaeosol samples

“…By dissolving the small particles, chemical extraction techniques may offer supplementary information on the changes that have taken place in the lithogenic fraction during the formation of the palaeosols. The acid-ammonium-oxalate/ferrous-iron (AAO-Fe 2+ ) extraction technique has yielded promising results in synthetic samples ( van Oorschot & Dekkers 2001). The acid-ammonium-oxalate/ferrous-iron (AAO-Fe 2+ ) extraction technique has yielded promising results in synthetic samples ( van Oorschot & Dekkers 2001).…”

“…Here, we aim to compare the results of the AAO-Fe 2+ extraction method for natural samples with a directly related study into the dissolution behaviour of synthetic samples ( van Oorschot & Dekkers 2001), to see whether these behave in a similar way. The dissolution behaviour of magnetic minerals from a loess-palaeosol sequence from South Moravia (Czech Republic) during treatment with the AAO-Fe 2+ extraction method will be discussed.…”

Stabilization of Organic Carbon via Chemical Interactions with Fe and Al Oxides in Gley Soils

“…Extraction with dithionite-citrate-bicarbonate (DCB) disrupts Al 3+ and Fe 3+ bonds between minerals and SOM by reductive dissolution and concurrently releases SOM from both weakly and strongly crystalline Al 3+ and Fe 3+ oxides into solution (von Lützow et al, 2007). To isolate oxalate-soluble Al, Fe, and bound OM, 0.02 M ammonium oxalate (pH 3) (Schwertmann, 1964;van Oorschot and Dekkers, 2001) was used in preference to 0.2 M ammonium oxalate to minimize oxalate contamination of extracted OM and remaining soil residues. In this study, weakly and then strongly crystalline Fe/Al oxides, along with the respective associated OM fractions, were extracted from soil subsamples for each replicate at each depth within each soil pit by sequential selective extraction using oxalate and then DCB.…”