Manganese Oxides In Soils Research Articles

Thallium sorption by soil manganese oxides: Insights from synchrotron X-ray micro-analyses on a naturally thallium-rich soil

Thallium (Tl) is a highly toxic trace metal. It occurs mostly as soluble monovalent Tl(I) and less frequently as poorly soluble trivalent Tl(III). Laboratory studies have shown that vacancy-containing hexagonal birnessites can sorb Tl with a very high affinity via a mechanism that involves the oxidation of Tl(I) to Tl(III) and strong complexation of Tl(III), whereas other manganese (Mn) oxides bind Tl(I) non-oxidatively and with lower sorption affinity. Information on the mode of Tl uptake by natural Mn oxides in soils, on the other hand, is still limited. In this study, we characterized the association of Tl with Mn oxides and Tl (redox) speciation in a naturally Tl-rich soil using micro-focused synchrotron X-ray absorption near edge structure (XANES) spectroscopy and X-ray fluorescence (XRF) chemical imaging. The results show that most soil Tl was Tl(I) associated with micaceous clay minerals in the soil matrix. High levels of Tl in soil Mn concretions, on the other hand, were mostly identified as Tl(III), suggesting that oxidative Tl uptake by vacancy-containing hexagonal birnessite was the main process of Tl accumulation in soil Mn concretions. The spectroscopic results in combination with chemical extractions and published sorption isotherms for Tl on synthetic Mn oxides suggest that the formation and transformation of natural Mn oxides in soils and sorption competition of Tl with major and trace metal cations determine the extent and mode of Tl uptake by soil Mn oxides. Methodologically, this study compares classical micro-XRF element mapping combined with point XANES analyses for spatially-resolved element speciation with high-resolution chemical imaging of entire sample areas, which is of great interest for the geochemical community in light of diffraction-limited storage ring upgrades to many synchrotron lightsources.

Accumulation and dynamics of manganese in raspberry

The aim of this study was to evaluate the dynamics of Mn in ‘soil - raspberry’ system on the area around the manganese ore deposits Radostovo in Bužim municipality. Atomic absorption spectroscopy was used to determine the concentration of Mn in soil and plant samples. Fe, Zn and Cu concentration in soil and raspberry plants was also subject of analysis, since these elements have antagonistic relationship with Mn in soils. The concentration of available Mn in soils was low, although the total Mn in the same soils exceeded the Mn toxic values noted in the scientific literature. The chemical and physical properties of the examined soils characterized by a relatively high pH value and good ability to store root-zone air certainly contributed to the decreasing release of available Mn2+ from manganese oxides in soils as well as Mn2+ oxidation to insoluble Mn3+ or Mn4+ ions, resulting in low uptake of Mn by plant roots. The results of study also showed that the absorbed Mn mostly accumulates in leaves and roots of raspberry, and much less in the stem and fruits. That rule in Mn distribution within raspberry plant is in fact identical to all food crops.

Oxidation of Added Mn(II) in Soils Observed by XANES Spectroscopy and Cr(III) Oxidation

Soil manganese oxides are highly reactive and can strongly influence soil chemical transformations even when present in relatively minor concentrations. The continued reactivity of these oxides is dependent on regeneration, yet the mechanisms of Mn(II) oxidation in soils are not completely understood. We examined oxidation of added Mn(II) in four soils with a reducible Mn content ranging from 9.1 to 319 mmol kg⁻¹ (0.05–1.75%). The Mn in these soils was concentrated in manganiferous oxide coatings or concretions ∼50–100 µm in diameter. The progress of oxidation of Mn(II) was measured by both Mn K-edge XANES spectroscopy and the ability of the soil to oxidize added Cr(III)Cl₃ to Cr(VI) (Standard Net Cr Oxidation Test). Addition of Mn(II) to a soil sample caused an initial decrease in the energy position of the main absorption edge in XANES spectra collected from areas of high Mn concentration, showing sorption of the added Mn(II). Repeated scans over 30–50 h showed movement of the main edge to a higher energy, close to that of the soil before treatment, demonstrating oxidation. Chromium oxidation initially decreased due to blockage of reactive sites by sorbed Mn(II). It then increased linearly over the same time period to values higher than the untreated soil, confirming the oxidation of the added Mn(II) and an increase in overall Mn oxide reactive sites. Oxidation continued even after exposure to strongly ionizing X-rays, suggesting a coupled biotic/abiotic pathway.

Degradation kinetics and estrogenic activity of 17β-estradiol removal by aqueous manganese dioxide

Natural and synthetic hormones have emerged as a new group of contaminants in soil and water systems. To better understand the processes affecting these compounds in soils and sediments, the kinetics of 17β-estradiol (E2) transformation by hydrous manganese oxide (δ-MnO2 were investigated as a function of reactant concentration, MnO2 concentration, pH and the presence of co-solutes. The reaction of E2 degradation by δ-MnO2 did not exhibit simple pseudo–first-order kinetics, although a good linear fit (R2 = 0.97) was obtained during the first 30 min, which was indicative of pseudo–first-order reaction kinetics in the first stage. The initial reaction rate (rinit) values of E2 degradation were enhanced with increasing E2, MnO2 and H+ concentration. The reaction orders for E2, MnO2 and H+ concentrations were 0.80, 0.72 and 0.07, respectively. The presence of metal ions and carboxylic acids had an inhibitory effect on rinit as a result of the decreased number of active surface sites in the presence of co-solutes. The same inhibitory effect on rinit was also observed in wastewater. Furthermore, the results showed that δ-MnO2 not only degraded E2 but also removed 62% and 48% of the estrogenic activity originating from E2 in ultrapure water and wastewater, respectively. This study demonstrated that natural manganese oxides in soils and sediments are likely to promote appreciable degradation of E2, and that reaction rates are strongly dependent on solution conditions. However, a combination of methods should be adopted in order to completely remove the estrogenic activity of E2.

Abiotic oxidation of 17β-estradiol by soil manganese oxides

The degradation of 17β-estradiol (E2) in sterile soil and Mn-free soil slurries was determined. In 0.075 g ml −1 soil slurry, E2 with an initial concentration of 0.0267 μmol g −1 was rapidly degraded and near equimolar estrone (E1) accumulated. A mass balance involving E2 and E1 existed throughout the reaction. The E2 degradation was thus an oxidation process and E1 was the only product. The concurrent release of Mn(II) during E2 oxidation and a lack of E2 oxidation in Mn-free soil slurry together demonstrated that soil manganese oxides were responsible for E2 oxidation. The degree of E2 oxidation was higher at high pH than at low pH, consistent with the fact that the reaction released protons. This study suggests that manganese oxides may be used as soil amendments to effectively oxidize E2 to less potent E1 in soil.

Kinetics of Oxytetracycline Reaction with a Hydrous Manganese Oxide

Tetracycline antibiotics comprise a class of broad spectrum antimicrobial agents finding application in human therapy, animal husbandry, aquaculture, and fruit crop production. To better understand the processes affecting these antibiotics in soils and sediments, the kinetics of oxytetracycline transformation by a hydrous manganese oxide (MnO2) were investigated as a function of reactant concentration, pH, and temperature. Oxytetracycline was rapidly degraded by MnO2. Initial reaction rates exhibited pronounced pH-dependence, increasing as pH decreased. Reaction of oxytetracycline with MnO2 was accompanied by generation of Mn(II) ions, suggesting oxidative transformation of the antibiotic. At pH 5.6, apparent reaction orders for oxytetracycline and MnO2 were 0.7 and 0.8. Reaction order with respect to H+ was 0.6 between pH 4 and 9. Initial reaction rates increased by a factor of approximately 2.4 for 10 degrees C temperature increases; the apparent activation energy (60 kJ x mol(-1)) was consistent with a surface-controlled reaction. Reactivity of tetracycline antibiotics toward MnO2 increased in the following order: rolitetracyline oxytetracycline < or =tetracycline approximately meclocycline < chlortetracycline. The initial rate of chlortetracycline degradation by MnO2 was substantially larger than that of the other tetracycline antibiotics investigated. MnO2 reactivity toward oxytetracycline decreased with time; a retarded rate equation was used to describe oxytetracycline reaction with MnO2 under declining rate conditions. This study indicates that natural manganese oxides in soils and sediments are likely to promote appreciable degradation of tetracycline antibiotics, and that reaction rates are strongly dependent on reaction time scale and solution conditions.

Soil Manganese Oxides and Trace Metals

Trace metal accumulation by Mn in synthetic oxides and soil nodules has been attributed to specific adsorption and oxidation at Mn oxide surfaces, yet little is known about trace metal interactions with Mn in bulk soil. We investigated competitive effects of trace metal pretreatment on Cr oxidation in well‐aerated, high‐Mn soils, as well as accumulation of added Pb, Co, and Cu by soil Mn using microfocused synchrotron x‐ray fluorescence (μSXRF). Short‐term equilibrations of divalent Mn, Co, Pb, Cu, and Ni with soil samples weighed to contain equivalent amounts of NH2OH·HCl‐extractable Mn resulted in substantial interference in Cr oxidation, confirming metal interactions with Cr‐oxidizing sites on Mn oxide surfaces. Interference by Cu and Pb was greatest in samples likely to be low in competing sorbents, that is, low‐pH soils and smaller samples of higher Mn soils, respectively. Strongest interference in Cr oxidation resulted from Mn and Co addition, suggesting specific affinity for soil Mn oxide surfaces, and was greatest in high‐pH, high‐Mn‐valence soils previously shown to have the greatest Cr oxidation capacity. Nickel showed the weakest effect. Micro‐SXRF scans revealed substantial spatial correlation of soil Mn with added Co and Pb, but Pb microdistribution was equally correlated with soil Fe. Only modest overlap of soil Mn with added Cu was observed. Our data suggest that specific affinity of Pb, Cu, and Ni for soil Mn oxides was weaker than that of Mn and Co. Higher Mn oxide valence may enhance sorption and subsequent oxidation of these oxidizable metals.

Oxidative transformation of triclosan and chlorophene by manganese oxides.

The antibacterial agents triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol) and chlorophene (4-chloro-2-(phenylmethyl)phenol) show similar susceptibility to rapid oxidation by manganese oxides (delta-MnO2 and MnOOH) yielding Mn(II) ions. Both the initial reaction rate and adsorption of triclosan to oxide surfaces increase as pH decreases. The reactions are first-order with respect to the antibacterial agent and MnO2. The apparent reaction orders to H+ were determined to be 0.46 +/- 0.03 and 0.50 +/- 0.03 for triclosan and chlorophene, respectively. Dissolved metal ions (Mn(II), Zn(II), and Ca(II)) and natural organic matter decrease the reaction rate by competitively adsorbing and reacting with MnO2. Product identification indicates that triclosan and chlorophene oxidation occurs at their phenol moieties and yields primarily coupling and p-(hydro)quinone products. A trace amount of 2,4-dichlorophenol is also produced in triclosan oxidation, suggesting bond-breaking of the ether linkage. The experimental results support the mechanism that after formation of a surface precursor complex of the antibacterial agent and the surface-bound Mn(IV), triclosan and chlorophene are oxidized to phenoxy radicals followed by radical coupling and further oxidation to form the end products. Compared to several structurally related substituted phenols (i.e., 2-methyl-4-chlorophenol, 2,4-dichlorophenol, 3-chlorophenol, and phenol), triclosan and chlorophene exhibit comparable or higher reactivities toward oxidation by manganese oxides. The higher reactivities are likely affected by factors including electronic and steric effects of substituents and compound hydrophobicity. Once released into the environment, partitioning of triclosan and chlorophene to soils and sediments is expected because of their relatively hydrophobic nature. Results of this study indicate that manganese oxides in soils will facilitate transformation of these antibacterial agents.

Oxidation of Chromium(III) to (VI) by Manganese Oxides

Manganese oxides in soils oxidize Cr from a stable form to a more toxic mobile form. The influence of Mn oxide diversity on Cr oxidation is the subject of this report. Oxidation of Cr(III) to Cr(VI) by coarse clay-size natural Mn oxides, birnessite, todorokite, and lithiophorite was studied at pH 4 and 7, and at 200 and 400 μM initial Cr(III) concentrations. The oxidation rate obeyed the first-order rate law at the 400 μM Cr(III) initial concentration; the 200 μM concentration was too low and reverse reactions may have interfered. Rate law is valid only far from equilibrium. The rate of oxidation was greater for todorokite and birnessite that contained the most quadrivalent Mn and least for lithiophorite that contained a greater proportion of trivalent Mn determined by x-ray photoelectron spectroscopy (XPS). The deviation of Mn oxidation state from the frequently assumed quadrivalent form in Mn oxides suggests the need for a thorough assessment of the ion species of Mn in Mn oxides that occur in soils. At 400 μM Cr(III), the rate of Cr oxidation by the pyrolusite sample was intermediate between birnessite and todorokite suggesting that the sample was not pure pyrolusite. Apparently, the synthesis process did not reach equilibrium with pyrolusite. The sample used as a chemical standard was apparently more soluble and more effective in oxidizing Cr(III) than would be expected for the natural mineral pyrolusite.

Oxidation of Chromium(III) to (VI) by Manganese Oxides

Manganese oxides in soils oxidize Cr from a stable form to a more toxic mobile form. The influence of Mn oxide diversity on Cr oxidation is the subject of this report. Oxidation of Cr(III) to Cr(VI) by coarse clay‐size natural Mn oxides, birnessite, todorokite, and lithiophorite was studied at pH 4 and 7, and at 200 and 400 μM initial Cr(III) concentrations. The oxidation rate obeyed the first‐order rate law at the 400 μM Cr(III) initial concentration; the 200 μM concentration was too low and reverse reactions may have interfered. Rate law is valid only far from equilibrium. The rate of oxidation was greater for todorokite and birnessite that contained the most quadrivalent Mn and least for lithiophorite that contained a greater proportion of trivalent Mn determined by x‐ray photoelectron spectroscopy (XPS). The deviation of Mn oxidation state from the frequently assumed quadrivalent form in Mn oxides suggests the need for a thorough assessment of the ion species of Mn in Mn oxides that occur in soils. At 400 μM Cr(III), the rate of Cr oxidation by the pyrolusite sample was intermediate between birnessite and todorokite suggesting that the sample was not pure pyrolusite. Apparently, the synthesis process did not reach equilibrium with pyrolusite. The sample used as a chemical standard was apparently more soluble and more effective in oxidizing Cr(III) than would be expected for the natural mineral pyrolusite.

Sensitivity of Soil Manganese Oxides

Effects of sample treatment must be well understood to avoid artifacts during analysis. The effect of drying and storage was examined on nine medium‐ to high‐Mn aerobic soils using extractable Mn(II), the Cr Oxidation Test, estimated soluble C, and XANES spectroscopy. Long‐term storage (430 d) at 3°C had little effect on the Cr test. Air drying at room temperature (25°C ± 3°C) caused a drop in the Cr test within 24 h, with a further decline to as low as 45% of the original after 72 h, and less than 2% after 264 d. Extractability of Mn with pH 4.8 NH4OAc increased nearly linearly over the same time period from 0.2 mmol kg−1 to as high as 2.3 mmol kg−1 Increases in the absorbance of the extract at 360 nm, an estimate of soluble C, were well correlated within each soil with the increase in Mn(II). Pre‐treatments to remove soluble organics did not cause any increases in the Cr test of dried samples. Therefore, the loss of Cr oxidizing ability appears to be due to reduction of the oxides, not because of increased reduction of the Cr(VI) formed. No changes in XANES spectra were found after short‐term air drying at room temperature, but in the three samples examined after 428 d of drying, the main‐edge position had a downward shift of about 1.5 eV, indicating reduction. These results confirm previous findings that studies on the reactivity of soil Mn oxides need to avoid sample drying.

Sensitivity of Soil Manganese Oxides

The examination of soils by x‐ray absorption near‐edge structure (XANES) spectroscopy can provide valuable clues for determining the structure and composition of Mn oxides. XANES experiments can be conducted at ambient temperatures using field‐moist samples. This feature is attractive in the study of soil Mn because of the well‐documented effects of sample drying on reactivity. The present study was undertaken to determine whether the analysis of field‐moist soils by XANES spectroscopy has an effect on the oxidation state of the Mn. Repeated scans were taken on the same spot using seven medium‐ to high‐Mn soils. In all 10 experiments with untreated soils, the main absorption edge dropped in relative energy in successive scans, indicating reduction of Mn. The change in eV was as high as 1.7 eV after 150 min of exposure time. After a series of scans showing reduction, small movement of the sample in the x‐ray beam and reexamination showed no reduction, indicating that the effect was limited to the x‐ray spot. Modeling the change with Mn(II) was successful and showed increases in reduced Mn between 6 and 20% after three to five repeated scans. The slopes of eV change vs. exposure time were remarkably similar in most experiments, even with large differences in the density of photons between runs. Comparisons of initial moist scans with those of recently air‐dried samples found little difference, suggesting minimal reduction in a single XANES scan under our experimental conditions.

Zinc Sorption by Manganese‐Oxide‐Coated Sand as a Function of pH

AbstractManganese oxides in soils may be sites for sorption of heavy‐metal cations, but the roles of pH‐dependent charge and oxide mineralogy remain unclear as controls on exchangeability of the metals. A model soil‐oxide system tested the effect of pH on the amount and form of Zn retained in exchangeable or nonexchangeable fractions on birnessite‐hausmannite‐coated sand or pyrolusite‐coated sand. Two Zn treatments, 250 and 2500 µmol/kg sand, were used to determine the effect of Zn concentration on the form of Zn retained. Surface charge for the birnessite‐hausmannite‐coated sand and pyrolusite‐coated sand increased across the pH range from 4 to 7.6, but surface charge was found to be a poor predictor of the amount and form of Zn retained even though the oxides increased Zn sorption by the sand. The distribution between the exchangeable and nonexchangeable Zn fractions changed from predominantly exchangeable to predominantly nonexchangeable Zn due to the oxide coatings and higher pHs. The difference in the exchangeable and nonexchangeable Zn retention by the two sands was attributed to mineralogical constraints on the type of surface functional groups. The mechanisms proposed to account for the nonexchangeable retention of Zn on both oxide‐coated sand surfaces were hydrolysis of the Zn followed by chemisorption to the oxide surface.

Roles of clays in soils

In soil science, the term clay refers to all particles less than 2 μm in diameter. Thus it includes layer silicates, oxides and other minerals. Clays are the source of many of the chemical and physical properties of soils that make them a useful medium for the growth of plants and for the less common uses such as a medium for the disposal of wastes. Clays add much of the diversity found in soils. The minerals in soil clays frequently differ from their counterparts in commercial deposits. Also, the behavior of soil clays is influenced by the associated minerals in the coarser fractions. Organic matter is an important reactant with clays of some soils, but it is beyond the scope of this review. The cation exchange properties of clays are among their most important properties in retaining plant nutrient ions (e.g., NH 4 +, K +, Ca 2+, Mg 2+, etc.). Cation selectivity of clays influences soils as a plant growth medium and as a disposal medium for wastes (e.g., radioactive and toxic metal ions). Native K in layer silicates of soils is the most important element provided to plants by illites and other micas. Clays contribute to the formation of soil structure by undergoing seasonal shrinking and swelling. Also, they are transported and form clay films that coat natural aggregates that characterize many friable soils. The dispersion and flocculation of clays are important reactions in the physical behavior of soils which in turn influence friability, water infiltration rate, erodibility and other behavioral properties. Vermiculite and smectite in soils frequently have Al 3+ or polymeric Al on the cation exchange sites. Thus the behavior of these minerals is different from structurally similar minerals in natural deposits. The Fe oxides in soils occur largely as goethite and hematite. Yet they contain Al substituted in their structures, consequently the crystals are smaller and less soluble than their ideal counterparts. Iron oxides contribute to the color, aggregation, and adsorptive properties of soils. Manganese oxides in soils contribute to the retention of trace metals (Co, Zn, Ba, Ni, etc.) and to the oxidation of Fe. Lithiophorite forms in acid soils thus marking another group of minerals that occurs in soils and that is influenced by Al in the structure or in interlayer positions as a result of weathering.

Iron and manganese oxide minerals in soils

ABSTRACTAccurate identification of iron and manganese oxides in soils presents great difficulty because, not only are they always in admixture, but the poor crystallinity of the species present leads to difficulties in interpretation of diffraction patterns. A method involving the combined use of electron microscopy, selected area electron diffraction and electron probe microanalysis on the same crystals gives unambiguous identification. Its application is described in relation to the various iron and manganese oxides found in a set of soils from all parts of the world. The occurrence of hausmannite in soils has been definitely established.

The adsorption of lead and other heavy metals on oxides of manganese and iron

Measurements were made of the adsorption of cobalt, copper, manganese, nickel, lead, and zinc on nine synthetic manganese oxides and three synthetic iron oxides, to determine the mechanism by which lead accumulates in the manganese oxides in soils. Adsorption of lead by the manganese oxides was up to 40 times greater than that by the iron oxides, and lead was adsorbed more strongly than any of the other ions studied by all of the oxides except goethite. This is considered to be the reason for the accumulation of lead in the manganese oxides in soils. No evidence was found for the oxidation of lead, nor for the formation of specific lead-manganese minerals.

The Manganese Oxides in Soils—A Review

Zeitschrift für Pflanzenernährung und BodenkundeVolume 131, Issue 3 p. 221-242 Originalarbeiten The Manganese Oxides in Soils—A Review R. M. McKenzie, R. M. McKenzie C.S.I.R.O., Division of Soils, Glen Osmond, S.A., 5064 AustraliaSearch for more papers by this author R. M. McKenzie, R. M. McKenzie C.S.I.R.O., Division of Soils, Glen Osmond, S.A., 5064 AustraliaSearch for more papers by this author First published: 1972 https://doi.org/10.1002/jpln.19721310302Citations: 30AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume131, Issue31972Pages 221-242 RelatedInformation