Structural characterization of iron oxides and hydroxides in the clay fraction of soils from the Inca civilization Moray terraces
We introduce the structural characterization of the iron oxides and hydroxides in the clay fraction from soil collected in Moray terraces, Peru. It is important since these terraces are considered as a major technological advancement in agriculture in Inca Civilization times. We utilized the following: techniques of selective dissolution by dithionite-citrate-bicarbonate (DCB) and sodium hydroxide (NaOH); analytical techniques of X-ray diffractometry (XRD); and transmission Msbauer spectroscopy (TMS). XRD of the untreated samples showed that all the terraces contain quartz and calcite. After a treatment with NaOH and DCB, the peaks from quartz kept defined; XRD analysis shows a well-crystallized Fe3+ oxide in all the analyzed samples, along with a mixture of quartz, stratified illite-montmorillonite-sanidine clay mineral and muscovite. The main peak of gypsum, observed by XRD in untreated samples, dissolved almost completely. In the TMS analysis it is observed the efficiency of NaOH to concentrate iron; concerning the DCB-treated samples, the area ratio of Msbauer absorption indicates an increase of Fe3+ sites. Besides, DCB treatment, sequentially applied four times, dissolved the poorly crystallized hematite.
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