Distribution of Fe-bearing compounds in an Ultisol as determined with selective chemical dissolution and Mössbauer spectroscopy

On this work, the iron oxide mineralogy of Chilean volcanic ashes derived soils have been reviewed, emphasizing on new finding linked to the application of Mössbauer spectroscopy. It has been established that free iron oxide layer contributes with positive variable surface charge to the clay-size soil particle, at soil pH. However, the importance of such contribution seems to depend on the evolutionary stage of the different volcanic soil orders, which defines the crystalline degree of their iron oxide contents. Mössbauer spectroscopy complemented with different physical, chemical and instrumental techniques revealed key aspects of iron oxide mineralogy on these Chilean volcanic soils. For instance, results for Ultisol revealed that the evolution of the soil particle could be followed just analysing the main component of their iron oxide mineralogy; thus, the iron oxide mineralogy change when passing from the volcanic ashes (magnetite), to sand-size magnetic separates (partially-oxidized magnetite), to silt-size (strongly-oxidized magnetite), and finally to clay-size (maghemite) soil samples. Therefore, it would seem that physical weathering of the Ultisol produces smaller and more oxidized particles. On the other hand, the Andisol samples, a young volcanic soil compared to Ultisol, seems to have a constant iron oxide mineralogy among all its different particle size fractions: paramagnetic Fe 2+ and Fe 3+ species with low crystalline degree, the last one possibly assignable to a ferrihydrite-like mineral. Therefore, on the case of Andisols, it seems that the high contents of organic matter somehow prevent mineral evolution towards higher oxidation and more crystalline levels, in agreement with past studies.

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“…An analogous behaviour is observed for Si and Al extracted by these methods (Pizarro et al, 2008a). (Pizarro et al, 2003).…”

Section: Chemically Treated Silt and Clay Fractionssupporting

confidence: 74%

Iron-bearing minerals from soils developing on volcanic materials from Southern Chile: Mineralogical characterisation supported by Mössbauer spectroscopy

Pizarro¹,

Escudey²,

Gacitúa³

et al. 2017

J. Soil Sci. Plant Nutr.

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“…In contrast, Iron-bearing minerals from soils developing on volcanic materials from Southern Chile analysis of the silt-size fraction from the same Ultisol revealed the dominant iron oxide to be oxidized magnetite (Pizarro et al 2000a and b). Finally, results from Pizarro et al (2008) revealed the presence of maghemite, goethite, and hematite minerals in the clay-size soil fraction from Ultisol. However, similar analysis of Andisol soil samples revealed the persistence of paramagnetic Fe 2+ and Fe 3+ species (the last one possibly assignable as a ferrihydrite-like mineral bonded to aluminosilicate structures) throughout all size fractions (Pizarro et al 2000a and b;2001;2008).…”

Section: Technological Applications Of Natural Iron Oxidesmentioning

confidence: 95%

“…Chilean volcanic Ultisols contain a diverse array of iron oxide minerals with generally higher crystalline order compared to Andisol (Mella and Kuhne 1985;Pizarro et al 2017) and possess different dominant iron oxide forms depending on the soil size-fraction: partially oxidised magnetite in the sand-size fraction, oxidized magnetite in the silt-size fraction, and maghemite in the clay-size fraction (Pizarro et al 2000a(Pizarro et al , 2000b(Pizarro et al , 2001(Pizarro et al , 2005(Pizarro et al , 2017 after the fifth, attributed to aluminium re-precipitation process over the solid particles (Manzo et al 2011). Kwan and Voelker (2003) NaOH treatments are presented on Figure 4 (Adapted from Pizarro et al 2008 andManzo et al 2011). Manzo et al (2011) since no more than 0.02 mg L -1 of soluble iron was quantified during catalysis assays.…”

Section: Fenton Reactionmentioning

confidence: 99%

Iron-bearing minerals from soils developing on volcanic materials from Southern Chile: Application in heterogeneous catalysis

Pizarro

Escudey

Gacitúa

et al. 2018

J. Soil Sci. Plant Nutr.

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Chilean soils derived from volcanic ashes are a natural source of iron oxides. Due to their properties, mineralogy, and surface characteristics, iron oxides from Chilean soils are potential candidates for technological applications such as heterogeneous catalysis. However, before a direct application in catalysis, pre-treatment methods are necessary to concentrate iron oxides from bulk volcanic soils. Here, we provide a comprehensive review of pre-treatment strategies for iron oxide concentration including physical separation and selective chemical dissolutive methods for application in catalytic processes, such as the water gas shift (WGS) and Fenton reactions. For preparation of WGS catalyst from volcanic soils, thermal treatment has been demonstrated to be effective, yielding enhanced results for Andisols compared to Ultisols. Based on mineralogical characterisation, it seems that WGS reaction efficiency depends on mineralogical phase shift and the changes of Fe 2+ /Fe 3+ ratio, produced through heating. In addition, Ultisols have shown as efficient catalysts in Fenton and Fenton-like processes, after application of physical and chemical pre-treatments to different size-fractions of the soil sample, improving the yield performance of catalysts. Magnetic separates from the Ultisol sand fraction (compared to the silt+clay fractions) demonstrate the best catalytic performance as Fenton reagent due to their natural magnetite and titanomagnetite content. Application of NaOH selective dissolutive treatment to silt+clay fraction of volcanic soils also produces Fenton and Fenton-like catalyst with improved performance. Our review indicates that catalytic performance can be explained not only by the iron oxide mineral content but also by their characteristics and magnetic properties.The application of the appropriate physical and chemical pre-treatment methods can modulate and enhance the catalytic capabilities of iron oxides from volcanic soils.

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“…The presence of crystalline minerals, such as kaolinite, halloysite, and Al/Fe oxides will be significant in the IPD mechanism in ultisols [5,35]. The way minerals, present on VADS, are interrelated or chemically spatially distributed, either being freely distributed throughout the soil mass or coating silt and clay grains, is determinant on their chemical role in the whole ion adsorption-desorption mechanisms [7]. The different mineral composition of VADS will have an impact on their different physical behavior, influencing the INIH adsorption rate, the adsorption mechanism involved, and the INIH adsorption capacity.…”

Section: Figure 3 (A) Pso Model For Adsorption Kinetics Of Gps On Ulmentioning

confidence: 99%

“…Allophane plays a key role in surface reactivity in andisols determining the availability of nutrients and controlling soil contaminant behavior [6]. Ultisols have a low amount of OM, relatively high amounts of Fe oxides in different degrees of crystallinity, low base saturation (<30%), high bulk density (0.8-1.1 Mg m −3 ), and high clay content (>40%) [2,7]. This last component provides a finer texture that allows a greater cohesion with respect to andisols [2,8].…”

Section: Introductionmentioning

confidence: 99%

Herbicides Mechanisms Involved in the Sorption Kinetic of Ionisable and Non Ionisable Herbicides: Impact of Physical/Chemical Properties of Soils and Experimental Conditions

Cáceres-Jensen¹,

Neira-Albornoz²,

Escudey³

2019

Kinetic Modeling for Environmental Systems

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Volcanic ash-derived soils (VADS, variable-charge soils) are predominant in some regions of the world, being of great importance in the agricultural economy of several emerging countries. Their amphoteric surface charge characteristics confer physical/chemical properties different to constant surface charge-soils, showing a particular behavior in relation to the herbicide adsorption kinetics. Volcanic soils represent an environmental substrate that may become polluted over time due to intensive agronomic uses. Solute transport models have contributed to a better understanding of herbicide behavior on variable-and constant-charge soils, being also necessary to evaluate the fate of herbicides and to prevent potential contamination of water resources. The following chapter is divided into four sections: physical/chemical properties of variable and constant-charge soils, kinetic adsorption models frequently used to obtain kinetic parameters of herbicides on soils, solute transport models to describe herbicide adsorption on VADS, and impact of experimental conditions of kinetic batch studies on solute transport mechanisms.

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Distribution of Fe-bearing compounds in an Ultisol as determined with selective chemical dissolution and Mössbauer spectroscopy

Cited by 3 publications

References 2 publications

Iron-bearing minerals from soils developing on volcanic materials from Southern Chile: Mineralogical characterisation supported by Mössbauer spectroscopy

Iron-bearing minerals from soils developing on volcanic materials from Southern Chile: Mineralogical characterisation supported by Mössbauer spectroscopy

Iron-bearing minerals from soils developing on volcanic materials from Southern Chile: Application in heterogeneous catalysis

Herbicides Mechanisms Involved in the Sorption Kinetic of Ionisable and Non Ionisable Herbicides: Impact of Physical/Chemical Properties of Soils and Experimental Conditions

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