Simultaneous incorporation of Mn and Al in the goethite structure

Álvarez, Mariana; Rueda, Elsa H.; Sileo, Elsa E.

doi:10.1016/j.gca.2006.11.012

Cited by 86 publications

(89 citation statements)

References 50 publications

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“…Close inspection of the micrographs (in the 1μm range) shows the following morphologies: round rodlike structures for pure goethite and an increase in the length-to-width ratio in crystal growth for Mn-substituted goethite as compared to pure goethite. This result is in agreement with previous studies [34][35][36]. Importantly, EDX measurements on the synthesized minerals showed the presence of manganese, homogeneity in the substitution for iron at the mineral surface to within the resolution of the method, and that the manganese did not exist as discrete phases within the goethite minerals.…”

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confidence: 93%

Molecular interactions of plutonium(VI) with synthetic manganese-substituted goethite

Schwaiger

Booth

et al. 2010

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SummaryPlutonium(VI) sorption on the surface of well-characterized synthetic manganese-substituted goethite minerals (Fe 1-x Mn x OOH) was studied using X-ray absorption spectroscopy. We chose to study the influence of manganese as a minor component in goethite, because goethite rarely exists as a pure phase in nature. Manganese X-ray absorption near-edge structure measurements indicated that essentially all the Mn in the goethite existed as Mn(III), even though Mn was added during mineral synthesis as Mn(II). Importantly, energy dispersive X-ray analysis demonstrated that Mn did not exist as discrete phases and that it was homogeneously mixed into the goethite to within the limit of detection of the method. Furthermore, Mössbauer spectra demonstrated that all Fe existed as Fe(III), with no Fe(II) present. Plutonium(VI) sorption experiments were conducted open to air and no attempt was made to exclude carbonate. The use of X-ray absorption spectroscopy allows us to directly and unambiguously measure the oxidation state of plutonium in situ at the mineral surface. Plutonium X-ray absorption near-edge structure measurements carried out on these samples showed that Pu(VI) was reduced to Pu(IV) upon contact with the mineral. This reduction appears to be strongly correlated with mineral solution pH, coinciding with pH transitions across the point of zero charge of the mineral. Furthermore, extended X-ray absorption fine structure measurements show evidence of direct plutonium binding to the metal surface as an inner-sphere complex. This combination of extensive mineral characterization and advanced spectroscopy suggests that sorption of the plutonium onto the surface of the mineral was followed by reduction of the plutonium at the surface of the mineral to form an inner-sphere complex. Because manganese is often found in the environment as a minor component associated with major mineral components, such as goethite, understanding the molecular-level interactions of plutonium with such substituted-mineral phases is important for risk assessment purposes at radioactively contaminated sites and long-term underground radioactive waste repositories. Previous work by Kaplan et al.[4] using laboratory and lysimeter studies showed that > 95% of plutonium migrating from a purposefully placed solid Pu IV (NO 3 ) 4 source remained within 1.25 cm of the source over an 11 year period under natural environmental conditions at the Department of Energy (DOE) Savannah River Site (SRS).Such work on large-scale environmental systems is an important part in uncovering essential components of the soil and mineral composition that controls plutonium redox chemistry. However, individual sorption and redox processes must also be tested on well-characterized model mineral phases that properly represent individual environmental In nature, manganese is rarely found as a pure mineral phase. It is often found as a minor component associated with major mineral phases, such as goethite. As a model to these environmental minerals, we have synthesiz...

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confidence: 93%

Molecular interactions of plutonium(VI) with synthetic manganese-substituted goethite

Schwaiger

Booth

et al. 2010

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“…These enrichments may reflect the substitution of Fe 2+ by Mn 2+ and Mg 2+ in the crystal structure of vivianite (Dijkstra et al, 2016;Frost et al, 2002;Nakano, 1992). In Fe oxides, the incorporation of cations such as Mn 3+ into the crystal structure affects the mineral stability and can result in higher acid dissolution rates of Fe oxides (Alvarez et al, 2007). At present, it is unknown whether the substitution of Fe 2+ in vivianite crystals by other cations affects the mineral stability and its susceptibility to sulfide dissolution.…”

Section: Introductionmentioning

confidence: 99%

Post-depositional formation of vivianite-type minerals alters sediment phosphorus records

et al. 2018

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Abstract. Phosphorus (P) concentrations in sediments are frequently used to reconstruct past environmental conditions in freshwater and marine systems, with high values thought to be indicative of a high biological productivity. Recent studies suggest that the post-depositional formation of vivianite, an iron(II)-phosphate mineral, might significantly alter trends in P with sediment depth. To assess its importance, we investigate a sediment record from the Bornholm Basin that was retrieved during the Integrated Ocean Drilling Program (IODP) Baltic Sea Paleoenvironment Expedition 347 in 2013, consisting of lake sediments overlain by brackish-marine deposits. Combining bulk sediment geochemistry with microanalysis using scanning electron microscope energy dispersive spectroscopy (SEM-EDS) and synchrotron-based X-ray absorption spectroscopy (XAS), we demonstrate that vivianite-type minerals rich in manganese and magnesium are present in the lake deposits just below the transition to the brackish-marine sediments (at 11.5 to 12 m sediment depth). In this depth interval, phosphate that diffuses down from the organic-rich, brackish-marine sediments meets porewaters rich in dissolved iron in the lake sediments, resulting in the precipitation of iron(II) phosphate. Results from a reactive transport model suggest that the peak in iron(II) phosphate originally occurred at the lake-marine transition (9 to 10 m) and moved downwards due to changes in the depth of a sulfidization front. However, its current position relative to the lake-marine transition is stable as the vivianite-type minerals and active sulfidization fronts have been spatially separated over time. Experiments in which vivianite was subjected to sulfidic conditions demonstrate that incorporation of manganese or magnesium in vivianite does not affect its susceptibility to sulfide-induced dissolution. Our work highlights that post-depositional formation of iron(II) phosphates such as vivianite has the potential to strongly alter sedimentary P records particularly in systems that are subject to environmental perturbation, such as a change in primary productivity, which can be associated with a lake-marine transition.

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“…2). Individual substitutions of foreign elements in the goethite structure are known to produce different effects on (Alvarez et al 2005(Alvarez et al , 2008Kaur et al 2010), whereas the substitution of Al, Cr and Cd decreased the dissolution rate of goethite (Alvarez et al 2007;Kaur et al 2010). However, the presence of Zn, Pb and Cd in di-and trimetal (Zn-Pb, Zn-Cd and Zn-Pb-Cd) incorporated goethite increased the dissolution rate of goethite (Kaur et al 2010).…”

Section: Dissolution Rate Of Soil Fe Oxides and Synthetic Goethite Atmentioning

confidence: 99%

“…Individual substitution of Al, Cr and Co into goethite structure decreases the dissolution rate of goethite in HCl (Schwertmann 1984;Lim-Nunez and Gilkes 1987;Ruan and Gilkes 1995). By contrast, the incorporation of Mn into goethite accelerated the dissolution rate compared with pure goethite (Lim-Nunez and Gilkes 1987;Schwertmann 1991;Alvarez et al 2007). More recently, Kaur et al (2010) found that the dissolution rate of single-metalsubstituted goethite was in the order: Zn-> Pb(II)-!Pb(IV)-> unsubstituted > Cd-> Cr-goethite.…”

Section: Introductionmentioning

confidence: 99%

Association of trace elements and dissolution rates of soil iron oxides

et al. 2014

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Abstract. In this study, nine Oxisols and five Ultisols from Thailand were used to determine the association of major and trace elements with iron (Fe) oxides. The Fe oxides were concentrated and the association of elements (Al, Ca, Cu, Cr, Mg, Mn, Ni, Pb, P, Si, V, Ti, Zn) with Fe was evaluated using batch dissolution in 1 M HCl at 208C. The dissolution behaviour of Fe oxide concentrates was determined using batch dissolution and flow-through reactors. In addition to Fe, both Al and Ti were present in significant amounts in the Fe oxide concentrates. Manganese was the most abundant trace element, and Cu, Zn, Pb and As concentrations were <250 mg kg -1 in most samples. The dissolution behaviour of Fe-oxide concentrates indicated that Al, Cr and V were mostly substituted for Fe 3+ in the structure of goethite and hematite. A significant proportion of Mn, Ni, Co, Pb and Si was also present within the structure of these minerals. Some Mg, Cu, Zn, Ti and Ca was also associated with Fe oxides. The dissolution kinetics of Fe oxide concentrates was well described by three models, i.e. the cube root law, Avrami-Erofejev equation and Kabai equation, with the dissolution rate constants (10 3 k) corresponding to the three models ranging from 0.44 to 6.11 h -1 , from 1.01 to 4.40 h -1 and from 0.03 to 4.12 h -1 , respectively. The k constants of Fe oxide concentrates in this study were significantly and negatively correlated with the mean crystal dimension derived from [110] and [104] of hematite, the dominant mineral in most samples. The steady-state dissolution rate of a soil Fe-oxide concentrate (sample Kk) was substantially higher than for synthetic goethite under highly acidic conditions; this is possibly due to the greater specific surface area of sample Kk than the synthetic goethite.Additional keywords: acid dissolution, batch method, Fe oxide concentrate, non-stirred flow through reactor method, total element concentration, tropical red soils.

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Simultaneous incorporation of Mn and Al in the goethite structure

Cited by 86 publications

References 50 publications

Molecular interactions of plutonium(VI) with synthetic manganese-substituted goethite

Molecular interactions of plutonium(VI) with synthetic manganese-substituted goethite

Post-depositional formation of vivianite-type minerals alters sediment phosphorus records

Association of trace elements and dissolution rates of soil iron oxides

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