Mobility Of Manganese Research Articles

Enhanced mobility of iron and manganese on Mars: Evidence from kinetic experiments and models

Several missions have reported complex alteration mineralogies on early Mars, which preserve environmental records of multiple water-rock-atmosphere interactions. The MSL and M2020 missions in Gale and Jezero have identified Fe and Mn-bearing secondary phases. These elements are used as tracers for the redox conditions on both Earth and Mars. However, to fully understand the short-lived and local-scale processes observed on Mars, it is necessary to go beyond thermodynamic models and experiments. Enhancing our ability to interpret the redox and hydrological conditions from the observed phase assemblage requires understanding the evolution of Fe and Mn during weathering. This study reports the results of kinetic alteration experiments and geochemical models conducted under Mars-like conditions. We tested variable pO2, pCO2, temperatures, and starting solutions. The results suggest that Fe is more mobile on Mars than on Earth, with a pseudo-equilibrium concentration that is kinetically controlled by dissolution and oxidation rates. Despite some initially modeled siderite precipitation, no siderite precipitation was observed in the altered powder. Solutions with higher acid concentrations were primarily controlled by dissolution kinetics, with both Fe and Mn being mobile, even when a minor amount of P, Fe, and S bearing secondary phases are formed. Based on our experimental results, we updated the model and conducted two large-scale sensitivity tests on our kinetic simulation. We confirmed that our experiments were too high in pO2 for siderite to form; however, we found that over a range of clearly oxidizing conditions from an equilibrium standpoint, Fe and Mn are mostly mobile, and siderite precipitation can occur. We were able to determine the pO2, pCO2 and the temporal space where Fe-oxide or siderite predominate or coexist, constraining the meaning of reducing or oxidizing conditions. Moreover, we also observed that siderite formation would require a much longer water residence time than Fe-oxide to precipitate, interpreted as higher weathering rates, or later evaporation required to effectively precipitate under any conditions. On ancient Mars, both Fe and Mn would be relatively mobile and prone to be leached from their host rock. Observing siderite or oxide would not primarily be a redox marker but would be a clue to a different hydrological regime. At the planetary scale, it would be challenging to form authigenic siderite during alteration. Although siderite would not indicate the presence of a particularly reducing atmosphere and that Mn-oxides are mainly pH controlled and do not require terrestrial-level amounts of oxygen, a collocated precipitation of siderite and Mn-oxides could also provide valuable information to constrain the redox environment of the ancient Mars.

Accumulation of Mn, Cu, and Zn in Flowers and Leaves of Catalpa bignonioides in an Urban Area Under Climate Change Conditions

Abstract Green areas are an important part of the urban landscape. Trees produce oxygen, provide shade, maintain soil moisture, and reduce the amounts of toxic gases and dust in the air. Due to the changing climate, species characteristic of other climatic zones, e.g. Catalpa bignonioides, are planted in urban parks in Poland, mainly due to the attractive appearance of the leaves and flowers. The aim of the study was to assess the content of Mn, Cu, and Zn in flowers and leaves of C. bignonioides in the urban park and to determine the value of bioconcentration coefficients (BCF) of these metals. The obtained results indicate that the flowers and leaves of C. bignonioides accumulate lesser amounts of manganese, copper, and zinc. It is a consequence of the limited bioavailability of these components in soils, due to too high pH values resulting from alkalinization of urban soils. The values of bioconcentration coefficients (BCF <1) confirm the low accumulation of Mn, Cu, and Zn in both leaves and flowers of C. bignonioides, due to the limited mobility of manganese, copper, and zinc compounds in the soils of the urban park and the low impact of falling dusts, which are the carriers of the analyzed components.

MIGRATION OF HEAVY METALS FROM MINE WASTE ROCK DUMP END ENVIRONMENTAL IMPACT ON GROUNDWATERS AND SEDIMENTS

The environmental impact of mine waste rock dump, located in the region of Srednogorie, Bulgaria on groundwaters and sediments was studied. The acid mine drainage with low pH (2.43 - 3.53), high electrical conductivity (1500 - 4400 μS cm-1), content of Fe, Mn, Cu, Zn, Al, As and high concentration of sulfates (540 - 6905 mg L-1) are formed after heavy rainfall. The content of heavy metals, except manganese, in groundwater was significantly lower than that in the acid mine drainage, and the pH was in the range of 5.43 to 6.62. Sediments in the non-consequential vicinity of the mine waste rock dump had a pH in the range of 2.86 - 4.53 and contained heavy metals and As at concentrations higher than those in the mineral waste due to precipitation, co-precipitation and sorption reactions. An increase in the copper and zinc content in the exchangeable and organic matter fractions was found in the sediment sample. A relationship was found between arsenic and iron concentration in the sediments, which was mainly due to the retention of arsenic in the Fe and Mn oxides fraction. The concentration of total Mn in the sediments was lower than that in the mining waste due to the high mobility of manganese.

Manganese Mobility in Gale Crater, Mars: Leached Bedrock and Localized Enrichments

AbstractIn Gale crater on Mars, the rover Curiosity has discovered evidence of fluid mobilization of the redox‐sensitive element manganese. We present results for Mn from Curiosity's Alpha Particle X‐ray Spectrometer (APXS), which show that the average MnO concentration in mudstone‐dominated sedimentary units (0.22 wt%) is about one‐half of the concentration in the average Mars crust (0.44 wt%). Geochemical trends indicate that Mn in the sedimentary bedrock, most of which has a basaltic provenance, was leached by chemical alteration and dissolution. In >350 vertical meters of mudstone‐dominated strata, the apparent leaching of Mn and retention of Fe in Fe‐O‐H phase(s) resulted in the fractionation of Fe and Mn, indicating relatively moderate Eh‐pH fluid conditions that were not highly alkaline, reducing, or oxidizing. Exceptions are fracture‐associated, silica‐rich haloes where both Mn and Fe were leached by low pH fluids. The rover also discovered Mn‐rich veins, nodules, and patchy, dark coatings on rock surfaces, which are variably associated with enrichments in Fe, P, Cl, and/or Zn. These Mn‐rich features represent ∼1% of the 1029 APXS measurements acquired over ∼25 km of rover traverse. A thermochemical model shows that dissolved Mn2+ could have been concentrated via evaporation, sublimation, and/or freezing. Manganese was then likely precipitated in localized features when >99.99% of the Mn2+‐bearing water was removed from the system. These findings indicate that Mn was mobile in Gale crater and therefore bioavailable as a potential energy source for life.

Calcination Temperature Effect in Catalyst Reactivity for the CO SELOX Reaction Using Perovskite-like LaBO3 (B: Mn, Fe, Co, Ni) Oxides

H2 production by conventional processes such as reforming reactions involves formation of some undesired products such as CO. Selective CO oxidation (SELOX) is a good alternative to reduce its concentration because it is a thermodynamically favorable process. Perovskite-like oxides (LaMO3) are used in this work to catalyze the CO-SELOX process and they were synthetized by the self-combustion method. All catalysts were calcined at different temperatures (400 °C–800 °C) to analyze its impact on the material physicochemical properties. Different analytical techniques were used to study changes in structural and chemical properties. Temperature-programmed reaction (TPRe), using CO oxidation and CO-SELOX, was used to measure the catalytic reactivity of perovskite-like oxides. It was found that catalytic activity decreases when calcination temperature (CT) increases and that is correlated with oxygen mobility, surface defects, and surface concentration of manganese or cobalt species. It is also found that there is a crystalline phase change in the solids when the CT increases from 500 to 600 °C. The high catalytic activity observed at low CT remained even if they were calcined below 600 °C, which implies the possibility of amorphous species having catalytic activity that do not require a well-structured perovskite.

Bioavailability and mobility of arsenic, cadmium, and manganese in gold mine tailings amended with rice husk ash and Fe-coated rice husk ash.

This study was conducted to determine the effects of rice husk ash (RHA) and Fe-coated rice husk ash (Fe-RHA) on the bioavailability and mobility of As, Cd, and Mn in mine tailings. The amendments were added to the tailings at 0, 5, 10, or 20% (w/w) and the mixtures were incubated for 0, 7, 15, 30, 45, and 60days. The CaCl2 extractable As, Cd, and Mn in the amended tailings were determined at each interval of incubation period. In addition, the tailings mixture was leached with simulated rain water (SRW) every week from 0day (D 0) until day 60 (D 60). The results showed that both RHA and Fe-RHA application significantly decreased the CaCl2-extractable Cd and Mn but increased that of As in the tailings throughout the incubation period. Consequently, addition of both RHA and Fe-RHA leached out higher amount of As from the tailings but decreased Cd and Mn concentration compared to the controls. The amount of As leached from the Fe-RHA-amended tailings was less than that from RHA-amended tailings. Application of both RHA and Fe-RHA could be an effective way in decreasing the availability of cationic heavy metals (Cd and Mn) in the tailings but these amendments could result in increasing the availability of anionic metalloid (As). Therefore, selection of organic amendments to remediate metal-contaminated tailings must be done with great care because the outcomes might be different among the elements.

The Impacts of Applying Metal(loid) Enriched Wood Ash to Soils on the Growth and Elemental Accumulation of Rice

The mobility and uptake of phosphorus, manganese, arsenic, copper, zinc and several other heavy metal(loid)s to rice shoots and grains were measured under controlled irrigation [flooded and non-flooded] conditions in a pot experiment. Doses of 0.1–1% (w:w) of a metal(loid)-rich wood ash containing ≤ 13,000 mg kg−1 phosphorus, manganese, arsenic, copper and zinc were applied to a study soil to determine the impacts of the ash on rice grain quality and the fate of metal(loid)s. Pore water and rice shoots and grains were analysed for beneficial and toxic elements derived from the ash, and Food-chain exposure modelling was applied to the experimental data thereafter to predict risk of onward impacts to human health. Concentrations of phosphorus and manganese in pore water increased with ash addition, though this did not enhance grain phosphorus or manganese. Zinc mobility was largely reduced over the course of the experiment, but appeared unrelated to ash dose. Arsenic presented the greatest mobility in pore water of all measured metal(loid)s (~ 2500 µg l−1), with shoot concentrations displaying clear dose and irrigation response. Although rice concentrations of arsenic in grain were the lowest of all measured metal(loid)s, risk-modelling of the data showed that even a 0.1% addition of the study ash to soil could expose a high rice consuming cohort to a vastly increased probability of deleterious health impacts. Whilst it is unlikely that contaminated ash would be knowingly applied to land, this study highlights that even singular applications of metal(loid) rich ash to agricultural soils could have negative effects on crops and forward impacts to human health. Other application scenarios, whereby lesser contaminated ashes are repeatedly applied to soils, warrant further work with regard to potential risks of accumulated metal(loid)s entering the food chain.

Metal Extractability in Binary and Multi-metals Spiked Calcareous Soils

ABSTRACTIn the present study, a laboratory experiment was designed to compare the 0.01 M calcium chloride (CaCl2) and diethylenetriaminepentaacetic acid (DTPA) extraction methods for their ability to predict cadmium (Cd), copper (Cu), iron (Fe), Manganese (Mn), nickel (Ni), and zinc (Zn) availability and mobility in five calcareous soils. The soils were spiked with different amounts of metals (0, 50, 100, 200, and 400 mg kg−1) both in binary (Cu and Zn; Ni and Cd; Fe and Mn) and in multi-systems (Cd, Cu, Fe, Mn, Ni, and Zn) and incubated for 1 months at field capacity. In metal-spiked soils, both extraction methods showed a linear relationship of extractable to total metals for all soils. The fraction of total metals extracted by DTPA was much higher than the fraction extracted by CaCl2, which was attributed to the formation of soluble metal-complexes in the complexing extracts calculated by the Visual Minteq program. DTPA extraction method showed higher selectivity for Cu over other metals both in binary and in multi-systems. Different order of metals extractability was found in binary and multi-systems for both extraction methods. Solid/solution distribution coefficient (Kd) was calculated by the ratio of the solid phase to soil solution concentration of metals extracted by CaCl2 or DTPA extraction methods. Both in binary and in multi-systems, the average Kd (l kg−1) of metals by soils were in the order of Mn (5398) > Fe (4413) > Zn (3376) > Cu (2520) > Ni (969) > Cd (350) in the CaCl2-extractable metals and Fe (35) ≥ Ni (34) > Zn (18) > Mn (11.2) > Cu (6.3) > Cd (4) in the DTPA-extractable metals. Results showed that among the six studied metals, Cd had the lowest Kd, implying a relative higher mobility in these calcareous soils. The Visual Minteq indicated that in the CaCl2-extraction method and in both binary and multi-systems the dominant species for Cu, Mn, Ni, and Zn were Cu2+, Mn2+, Ni2+ and Zn2+, respectively, while for Cd and Fe, the dominant species were CdCl+ and Fe(OH)2+, respectively.

Potential Release of Metals from Tailings and Soil at the Hamekasi Iron Mine, Hamadan, Iran

This study focused on acid neutralization reactions and the effects of water composition on the release and mobility of metals from mine tailings. The aims of this study were to: investigate leaching of metals from neutral mine tailings, determine the factors responsible for metal leaching, and investigate potential metal filtering by the soil. Tailings and soil samples were collected from an iron mine and analyzed. Equilibrium thermodynamic data and metal fractionation were then used to predict precipitation/dissolution of minerals and ion adsorption/desorption. Three column experiments were designed. The first column was filled with tailings, while the second column contained tailings above a layer of soil; both were leached with distilled water as rainfall. The third column was packed with soil and percolated with synthetic groundwater. The results indicated that iron (Fe) and zinc (Zn) mobility are mainly controlled by precipitation–dissolution mechanisms, while sorption onto oxides and carbonates limit the mobility of copper (Cu) and nickel (Ni). Cadmium (Cd) and manganese (Mn) mobility are affected by both mechanisms. Water discharging from column 3 (soil washed with groundwater) contained high concentrations of dissolved metals, indicating that water composition played an important role in metal mobility. Buffering minerals like carbonates and hornblende, chlorite, and albite decreased acid generation.

The mobility of phosphorus, iron, and manganese through the sediment–water continuum of a shallow eutrophic freshwater lake under stratified and mixed water-column conditions

The management of external nutrient inputs to eutrophic systems can be confounded due to a persistent pool of phosphorus (P) in lake sediments. The behaviors of P and trace metals depend largely on the reductive dissolution of amorphous iron (Fe) and manganese (Mn) (oxy)hydroxides in sediments; however, a holistic understanding of these dynamics in relation to the broader ecological and hydrodynamic conditions of the system remains elusive. We used a high-frequency monitoring approach to develop a comprehensive conceptual model of P, Mn, and Fe dynamics across the sediment water continuum of a shallow bay in Lake Champlain (Missisquoi Bay, USA). The greatest release of sediment P, Mn, and Fe occurred under stable hydrodynamic conditions, particularly during the onset of the cyanobacterial bloom and was associated with low available P and the accumulation of soluble Mn and Fe above the sediment–water interface (SWI). During the warmest part of the season, bloom severity and sediment P release was partially regulated by hydrodynamic drivers, which changed on hourly time scales to affect redox conditions at the SWI and bottom water concentrations of soluble P, Mn, and Fe. A geochemically distinct increase in soluble P and Fe concentrations, but not Mn, marked the influence of riverine inputs during a late season storm disturbance. Despite continued depletion of the reactive sediment P and metals pool into the bloom period, declining temperatures and a well-mixed water column resulted in bloom senescence and the return of P, Mn, and Fe to surface sediments. The closed cycling of P and metals in Missisquoi Bay poses a significant challenge for the long-term removal of P from this system. Multiple time-scale measures of physical and biogeochemical changes provide a basis for understanding P and trace metals behavior across sediments and the water column, which shape seasonally variable cyanobacterial blooms in shallow eutrophic systems.

Ugotavljanje vzrokov za pojavljanje amonija in železa v vodnem viru Borovniški vršaj

The article deals with chemical and isotopic properties of Borovnica alluvial fan groundwater. Increased concentrations of ammonium and iron were detected in well VB-3 of the Borovnica alluvial fan pumping Station. On the basis of analyses it was found out that increased concentrations of both elements are linked to the hydrogeological conditions in the aquifer area. In the upper part of the Borovnica alluvial fan aquifer, layers of clay prevent the access of oxygen to groundwater. This fact, together with the presence of organic matter in the aquifer, creates reduction conditions causing the mobility of iron and manganese in groundwater and the transformation of nitrogen from nitrate into ammonium form. Water from the lower aquifer contains more dissolved oxygen, and on the basis of tritium presence it can be concluded that the water is old up to 50 years. Wells VB-5 and VB-6 capture water from the lower pleistocene aquifer, while well VB-3 recharges also with water from the upper holocene aquifer.

Enhanced Dissolution of Manganese Oxide in Ice Compared to Aqueous Phase under Illuminated and Dark Conditions

Manganese is one of the common elements in the Earth's crust and an essential micronutrient for all living things. The reductive dissolution of particulate manganese oxide is a dominant process to enhance mobility and bioavailability of manganese for the use of living organisms. In this work, we investigated the reductive dissolution of manganese oxides trapped in ice (at -20 °C) under dark and light irradiation (visible: λ > 400 nm and UV: λ > 300 nm) in comparison with their counterparts in aqueous solution (at 25 °C). The reductive dissolution of synthetic MnO₂, which took place slowly in aqueous solution, was significantly accelerated in ice phase both in the presence and absence of light: about 5 times more dissolution in ice phase than in liquid water after 6 h UV irradiation in the presence of formic acid. The enhanced dissolution in ice was observed under both UV and visible irradiation although the rate was much slower in the latter condition. The reductive dissolution rate of Mn(II)(aq) (under both irradiation and dark conditions) gradually increased with decreasing pH below 6 in both aqueous and ice phases, and the dissolution rates were consistently faster in ice under all tested conditions. The enhanced generation of Mn(II)(aq) in ice can be mainly explained in terms of freeze concentration of electron donors, protons, and MnO₂ in liquid-like ice grain boundaries. The outdoor solar experiment conducted in Arctic region (Ny-Ålesund, Svalbard, 78°55'N) also showed that the photoreductive dissolution of manganese oxide is enhanced in ice. The present results imply that the dissolution of natural minerals like manganese oxides can be enhanced in icy environments such as polar region, upper atmosphere, and frozen soil.

Manganese mobility in soils under the impact of alkaline dust emission

Manganese mobility in soils under the impact of alkaline dust emission

Evolution of sediment metal concentrations in a tidal marsh restoration project

The combination of flood prevention and tidal marsh restoration will be implemented on a large scale in the Schelde estuary (Belgium). Densely populated and industrialized, this estuary was found to be severely contaminated with trace metals. In this study we evaluated the effect of tidal restoration on sediment trace metal concentrations. To asses historical contamination of embanked-, a restored- and natural tidal areas, deep sediment cores were sampled while the evolution of metal concentrations was determined by means of superficial samples taken during 10 sampling campaigns spread over the first 3years of the restoration project. Metal concentrations in the natural tidal marsh reflected the estuaries' contamination history. Fertilization by irrigation caused high metal concentrations in superficial soil layers of some embanked areas. However, reintroduction of the tide resulted in deposition of a new sediment layer with lower metal concentrations, comparable to the natural tidal marsh. Despite diagenetic mobility of manganese no diagenetic movements of the trace metals were observed during these first three years. Removal of metals from the estuary and burial of contaminated sediments in the restored site emphasize the potential of these restoration projects to decrease metal contamination risks. However, more research under field conditions on the effects of changes in land use and inundation related changes in metal bioavailability is needed to draw clear conclusions on the environmental consequences.

Mobility of Manganese in a Compacted Residual Gneissic Soil Under Laboratory Conditions

Given the shortage of information available in the literature on transport parameters of heavy metals in Brazilian tropical soils, the mobility of manganese (Mn2+) in a residual gneissic compacted soil is studied in this work. Manganese can be found in toxic concentrations in landfill leachate, besides being one of the main contaminants from acid mine drainage. Column tests were performed in two groups of compacted soil samples to determine the manganese retardation factor. The sample groups presented slightly different soil compaction degrees and water contents. Soil samples were initially saturated by upward percolation of distilled water without applied counter pressure. A multi-species contaminant solution was then percolated through the soil columns. A different behavior of the hydraulic conductivity along time was observed between the two groups, during water as well as solution percolation. Manganese mobility was observed to be independent of soil hydraulic conductivity, k, for the range of k-values attained in this investigation, emphasizing the importance in evaluating the mobility of this metal in compacted soil barriers. Even when these barriers present low hydraulic conductivity values, this cation high mobility may cause it to reach soil layers below the compacted layer resulting in groundwater contamination.

Controlled variation of redox conditions in a floodplain soil: Impact on metal mobilization and biomethylation of arsenic and antimony

An automated biogeochemical microcosm system allowing the control of redox potential (E H) in soil suspensions was used to assess the effect of E H on the mobility of cadmium (Cd), copper (Cu), nickel (Ni), zinc (Zn), iron (Fe), and manganese (Mn) as well as on the methylation of arsenic (As) and antimony (Sb) in a contaminated and slightly acidic floodplain soil. The experiment was conducted under stepwise variation from reducing (approximately −300 mV at pH 5) to oxidizing (+ 600 mV at pH 5) conditions. The E H was found to be an important factor controlling the dynamics of studied compounds and elements. Concentrations of Cd, Cu, Mn, Ni, and Zn in solution were low at low E H and increased with rising E H what might be attributed to the interaction with dissolved organic carbon (DOC), Mn, and precipitation as sulphides. Redox potential and pH correlate significantly with Cd, Ni, Cu, Zn, and Mn. Total Fe concentrations in solution were high at low E H and dropped sharply at E H > 350 mV at pH 5 to lower values due to the formation of Fe (hydr)oxides. Other metals did not adsorb to or co-precipitate with Fe, which may be attributed to the low pH (between 4.4 and 5.3) amongst other factors. Concentrations of inorganic arsenic (As i) and antimony (Sb i), momomethyl arsenic (MMAs), monomethyl antimony (MMSb), and dimethyl arsenic (DMAs) in solution decreased significantly with rising E H, indicating that low E H promotes the mobility of these compounds.

Investigation on bioavailability of some essential and toxic elements in medicinal herbs

Trace and major elements were determined in medicinal herbs (Cynara scolymus, Matricaria chamomilla, Artemisia absinthium L., Achillea millefolium, and Inula britannica) as well as in rhizosphere soil samples. Based on the results obtained after microwave-acid-assisted digestion (nitric acid + hydrogen peroxide) and single-step extraction (ammonium acetate), the real and potential acidity and redox potential of the soils, uptake, mobility, and bioavailability of potassium, calcium, magnesium, iron, manganese, copper, zinc, nickel, chromium, lead, and cadmium are discussed. By calculating the bioconcentration factors and their deviation from the recommended values, elevated concentrations, were explained in terms of contamination and pollution. The concentrations measured in both plants and soil samples were below maximum allowable concentration ranges considered for the European Union.

Mobility of Iron and Manganese within Two Citrus Genotypes after Foliar Applications of Iron Sulfate and Manganese Sulfate

ABSTRACT Seedlings of sour orange (Citrus aurantium L.) and Carrizo citrange (C. sinensis L. cv. Washington navel x Poncirus trifoliata)] were grown in plastic pots containing a sand: perlite mixture and watered with a modified Hoagland No 2 nutrient solution throughout the experiment. Three-months-old plants were divided in three groups and sprayed with 0.018 M iron sulfate (FeSO4 .7H2O), 0.018 M manganese sulfate (MnSO4 .H2O), or deionized water. Two months later, plants were harvested and divided into top leaves that grown after the treatments, basal leaves that existed prior to the treatments, stems that partially came in contact with the spray, and roots. The manganese (Mn) spray resulted in a significant increase of Mn concentrations in top leaves, basal leaves, stems and roots of sour orange, and in top leaves, basal leaves, and stems of Carrizo citrange. The iron (Fe) spray significantly increased the concentrations of Fe in the stems and basal leaves of both genotypes. For both genotypes, transport of Mn from basal (sprayed) leaves to top (unsprayed) ones was found. However, the results of this experiment did not give any evidence neither for Mn translocation from sprayed tissues to roots nor for Fe transport from sprayed tissues to unsprayed ones (top leaves, roots). Mn and Fe were found to be relatively mobile and strictly immobile nutrients, respectively, within citrus plants after their foliar application as sulfate salts.

Distribution and mobility of manganese in the hyperaccumulator plant Phytolacca acinosa Roxb. (Phytolaccaceae)

The distribution and mobility of manganese (Mn) in the hyperaccumulator plant species Phytolacca acinosa Roxb. (Phytolaccaceae) were investigated in a hydroponic system. The plants were exposed to 2 or 5 mM Mn for up to 28 days. For any given plant, the Mn content in the mature leaves (nos. 5–9) was always higher than that in the old (nos. 1–4) and young leaves (nos. 10–14). Within the different parts of a leaf, Mn was preferentially accumulated in the leaf marginal area, where the observed level was threefold higher than that in the midrib. Cross-sectional analysis of the leaf revealed that the concentration of Mn was higher in the leaf epidermis than in the mesophyll. Cell fractionation analysis with P. acinosa leaves showed that most of the Mn (78.4%) was present in the final supernatant fraction (following centrifugation at 20,000 g for 45 min). The distribution of Mn in the leaves of P. acinosa was controlled mainly by the transpiration rate. Our investigation demonstrated that Mn was readily transported from the roots to shoots of P. acinosa but that it could not be remobilized readily after it reached leaves.

Molecular Dynamics Simulations of Lix Mn2O4 Spinel Solid Solutions with Simple Potential Models

Molecular dynamics simulations of Li x Mn2O4 (0 < x ≤ 1) spinel solid solutions were carried out with the use of simple pair potentials available in the literature. The results demonstrate that computer simulations using the existing potentials with an exponential repulsion term fail to adequately reproduce appreciable Li+ mobility in a stable (near-zero mobility of the manganese and oxygen ions) crystalline phase. Lennard-Jones potentials make it possible to simulate such a phase at high temperatures (on the order of 1000 K).