Concentrations Of Manganese Oxides Research Articles

Agro waste as a source of bioactive glass for targeted drug delivery and bone implantation

The present work describes the synthesis of biocompatibe alkali-free glasses utilizing the agricultural waste rice husk and eggshells. A series of glasses with basic composition SiO2–P2O5–MgO–CaO has been synthesized using melt-quench technique, where P2O5 is partially replaced by MnO. These glasses are characterized to assess their in-vitro reactivity with the help of X-Ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, fourier transform infrared spectroscopy, and microwave plasma atomic emission spectroscopy techniques before and after soaking in the simulated body fluid solution. Further, drug loading and release studies are carried out with the help of UV–Visible spectrophotometer. Wherefore, a multivariable non-linear regression model has been developed to predict the release rate at different manganese oxide concentrations. The proposed model shows a high Pearson correlation coefficient between the observed and predicted absorbance. These results designate that low-cost agro-waste derived alkali-free glasses have potential in medical applications in drug delivery as well as it helps in environmental pollution management.

Retracted] Effect of Manganese Ions on Spectroscopic and Insulating Properties of Aluminophosphate Glasses

The melt‐quenching technique was used to produce 39CdO–10Al2O3‐(51‐x) P2O5: xMnO glasses (x = 0, 0.1, 0.2, 0.3, and 0.4 wt.%). Various stability factors were calculated and presented from DTA analysis. The stability of the glass network appears to increase with the increase of MnO concentration, according to the findings. IR spectral analysis of these glasses exhibited several symmetrical and asymmetrical bands due to phosphate groups. The observed change in these band intensities with the rise in MnO concentrations, ranging from 0.1 wt.% to 0.4 wt.%, shows an increase in the stability of the glass network. Optical absorption analyses of these glasses revealed an absorption band that shifted from 500 to 488 nm as the concentration of manganese oxide (MnO) increased from 0.1 wt.% to 0.4 wt.%, indicating that Mn2+ ions were gradually converted into Mn3+ ions. EPR spectra of these glasses were characterized by two signals due to Mn2+ and Mn3+ ions. Observations on these signal intensity variations revealed an increase in stability of the glass network with the increase of MnO concentration from 0.1 wt.% to 0.4 wt.%. Parameters, which describe the insulating characteristics, for example, dielectric constant, ε, dielectric loss, tan δ, and AC conductivity σac, were determined in relation to frequency (103 Hz to 105 Hz) and temperature (20°C to 400°C) and presented in the dielectric analysis of these glasses.

Iron and manganese speciation and cycling in glacially influenced high-latitude fjord sediments (West Spitsbergen, Svalbard): Evidence for a benthic recycling-transport mechanism

Glacial environments may provide an important but poorly constrained source of potentially bioavailable iron and manganese phases to the coastal ocean in high-latitude regions. Little is known about the fate and biogeochemical cycling of glacially derived iron and manganese in the coastal marine realm. Sediment and porewater samples were collected along transects from the fjord mouths to the tidewater glaciers at the fjord heads in Smeerenburgfjorden, Kongsfjorden, and Van Keulenfjorden along Western Svalbard. Solid-phase iron and manganese speciation, determined by sequential chemical extraction, could be linked to the compositions of the local bedrock and hydrological/weathering conditions below the local glaciers. The concentration and sulfur isotope composition of chromium reducible sulfur (CRS) in Kongs- and Van Keulenfjorden sediments largely reflect the delivery rate and isotope composition of detrital pyrite originating from adjacent glaciers. The varying input of reducible iron and manganese oxide phases and the input of organic matter of varying reactivity control the pathways of organic carbon mineralization in the sediments of the three fjords. High reducible iron and manganese oxide concentrations and elevated metal accumulation rates coupled to low input of “fresh” organic matter lead to a strong expression of dissimilatory metal oxide reduction evidenced in very high porewater iron (up to 800μM) and manganese (up to 210μM) concentrations in Kongsfjorden and Van Keulenfjorden. Sediment reworking by the benthic macrofauna and physical sediment resuspension via iceberg calving may be additional factors that promote extensive benthic iron and manganese cycling in these fjords. On-going benthic recycling of glacially derived dissolved iron into overlying seawater, where partial re-oxidation and deposition occurs, facilitates the transport of iron across the fjords and potentially into adjacent continental shelf waters. Such iron-dominated fjord sediments are likely to provide significant fluxes of potentially bioavailable iron to coastal waters and beyond. By contrast, low delivery of reducible iron (oxyhydr)oxide phases and elevated organic carbon mineralization rates driven by elevated input of “fresh” marine organic matter allow organoclastic sulfate reduction to dominate carbon remineralization at the outer Smeerenburgfjorden sites, which may limit iron fluxes to the water column.

Regional patterns of bioturbation and iron and manganese reduction in the sediments of the southeastern Bering Sea

Regional patterns of iron (Fe) and manganese (Mn) reduction rates across the shelf and slope of the southeastern Bering Sea, as well as the relative importance of these pathways in sedimentary organic matter remineralization, were investigated during the spring and summer of 2009. Reduction rates of Fe and Mn were calculated using depth profiles of solid-phase iron and manganese oxide concentrations and bioturbation coefficients, Db, determined from profiles of excess 234Th. Iron reduction was found to be a significant pathway for carbon mineralization across the shelf, with an average rate of 1.74mmolm−2d−1. However, Fe reduction rates higher than 6mmolm−2d−1 were calculated, and a significant regional pattern was observed, with highest rates found on the northern shelf, and dropping toward the south and offshore. Conversely, Mn oxide reduction was found to be of minor significance, with low reduction rates in all regions, averaging only 0.09mmolm−2d−1 across the shelf, and accounting for no more than 5% of total carbon oxidation in any region. These results indicate that Fe oxide reduction is a significant pathway for carbon remineralization in the northern and middle-shelf regions, where organic matter deposition rates and benthic biomass are high. Additionally, this work provides insight into the potential role of sedimentary iron reduction as a source of bioavailable Fe in this region.

Three manganese oxide-rich marine sediments harbor similar communities of acetate-oxidizing manganese-reducing bacteria

Dissimilatory manganese reduction dominates anaerobic carbon oxidation in marine sediments with high manganese oxide concentrations, but the microorganisms responsible for this process are largely unknown. In this study, the acetate-utilizing manganese-reducing microbiota in geographically well-separated, manganese oxide-rich sediments from Gullmar Fjord (Sweden), Skagerrak (Norway) and Ulleung Basin (Korea) were analyzed by 16S rRNA-stable isotope probing (SIP). Manganese reduction was the prevailing terminal electron-accepting process in anoxic incubations of surface sediments, and even the addition of acetate stimulated neither iron nor sulfate reduction. The three geographically distinct sediments harbored surprisingly similar communities of acetate-utilizing manganese-reducing bacteria: 16S rRNA of members of the genera Colwellia and Arcobacter and of novel genera within the Oceanospirillaceae and Alteromonadales were detected in heavy RNA-SIP fractions from these three sediments. Most probable number (MPN) analysis yielded up to 10(6) acetate-utilizing manganese-reducing cells cm(-3) in Gullmar Fjord sediment. A 16S rRNA gene clone library that was established from the highest MPN dilutions was dominated by sequences of Colwellia and Arcobacter species and members of the Oceanospirillaceae, supporting the obtained RNA-SIP results. In conclusion, these findings strongly suggest that (i) acetate-dependent manganese reduction in manganese oxide-rich sediments is catalyzed by members of taxa (Arcobacter, Colwellia and Oceanospirillaceae) previously not known to possess this physiological function, (ii) similar acetate-utilizing manganese reducers thrive in geographically distinct regions and (iii) the identified manganese reducers differ greatly from the extensively explored iron reducers in marine sediments.

A long-term bench-scale investigation of permanganate consumption by aquifer materials

In situ chemical oxidation (ISCO) applications using permanganate involve the injection or release of permanganate into the subsurface to destroy various target contaminants. Naturally occurring reduced components associated with aquifer materials can exert a significant oxidant demand thereby reducing the amount of permanganate available for the destruction of contaminants as well as reducing the overall rate of oxidation. Quantification of this natural oxidant demand (NOD) is a requirement for site-specific assessment and the design of cost-effective oxidant delivery systems. To further our understanding of the interaction between permanganate and aquifer materials, aerobic and anaerobic aquifer materials from eight representative sites throughout North America were tested in a series of systematic bench-scale experiments. Various permanganate to aquifer solids mass loading ratios at different initial permanganate concentrations in well-mixed batch reactors were monitored for > 300 days. All NOD temporal profiles demonstrated an initial fast consumption rate followed by a persistent slower consumption rate. The data generated show that the mass loading ratio, the initial permanganate concentration, and the nature and quantity of reduced aquifer material species are the main factors controlling permanganate consumption rates. A higher initial permanganate concentration or a larger mass loading ratio produced a larger fast NOD consumption rate and generated a corresponding higher maximum NOD value. Hence, both the NOD temporal profile and the maximum NOD are not single-valued but are heavily dependent on the experimental conditions. Predictive relationships were developed to estimate the maximum NOD and the NOD at 7 days based on aquifer material properties. The concentration of manganese oxides deposited on the aquifer solids was highly correlated with the mass of permanganate consumed suggesting that passivation of NOD reaction sites occurred due to the formation of manganese oxide coating on the grains. A long-term NOD kinetic model was developed assuming a single fast and slow reacting oxidizable aquifer material species, passivation of NOD reaction sites, and the presence of an autocatalytic reaction. The developed model was able to successfully capture the observed NOD temporal profiles, and can be used to estimate in situ NOD behavior using batch reactor experimental data. The use of batch tests to provide data representative of in situ conditions should be used with caution.

Effectiveness of an Open Limestone Channel in Treating Acid Sulfate Soil Drainage

An open limestone channel (OLC) was constructed within an existing drain to treat the acidic and metal-rich drainage waters generated from an acid sulfate soil (ASS) catchment. The OLC was constructed downstream of a catchment pump and it consisted of a series of ponds and limestone sections. The accumulation of sediment over the limestone, preventing contact of limestone with acidic water, was the greatest problem impacting the OLC in its first year of operation. The continuous or sporadic operation of the catchment pump (at 120 l/s) was not sufficient to flush sediment from the limestone. The accumulation of large amounts of sediment onto the limestone reduced the amount of alkalinity and calcium released into solution. However, if the sediment is removed by agitating the limestone then an equivalent or greater amount of alkalinity may be added to solution and more metals removed from solution compared to fresh limestone. The coating on the limestone had a high concentration of manganese oxides in addition to slightly lower concentrations of aluminium and iron. Removal of these metals from the water was due to the increase in pH produced by limestone dissolution in addition to sorption reactions of the existing coating which had natural microbial activity.

Thermal stability of metal-supported catalysts for reduction of cold-start emissions in a wood-fired domestic boiler

The aim of the present work is to develop a catalyst based on a mixture of manganese oxides and platinum supported on a metallic monolith for abatement of emissions from wood combustion, particularly during the cold-start phase. The activity and the thermal stability of the catalysts have been studied in the laboratory, before performing tests in a wood-stove. The effect of the hydrothermal treatment at 900°C on the adherence of the washcoat onto a metallic substrate was studied using scanning electronic microscope. It revealed well-adhering washcoat onto the metallic support due to the growth of the alumina whiskers during the treatment. The influence of the amount of washcoat, as well as the influence of the concentration of manganese oxides in it (Mn: 5 to 20 mol%/Al 2O 3) on the activity of fresh and hydrothermally-treated catalysts were studied. The activity tests were carried out using a mixture of carbon monoxide, naphthalene and methane in the presence of air, steam and carbon dioxide to resemble the flue gases from wood combustion. On the fresh catalysts, containing the same total amount of manganese, a high concentration of manganese oxides in the washcoat favoured the oxidation of carbon monoxide and naphthalene, whereas a lower concentration of manganese oxides in the washcoat gave higher activity for the oxidation of methane. An increased total amount of manganese oxides in the catalysts, which had the same amount of washcoat, resulted in an increase in activity for the oxidation of the three combustibles. After thermal treatment at 900°C for 270 h in steam, most of the manganese oxide catalysts were activated for the oxidation of carbon monoxide and naphthalene while only being slightly deactivated for the oxidation of methane. The addition of manganese oxides in the washcoat, however, lowers the temperature of the γ- to α-alumina phase transformation. Platinum (0.5 mol%) was added to the manganese oxide (10 mol%) catalyst to improve its activity. A platinum catalyst was also tested for comparison. The platinum and the mixed catalysts showed similar activity for the oxidation of carbon monoxide and naphthalene, while the mixed catalysts were more active for the oxidation of methane. A similarly mixed MnO x –Pt (10–0.5 mol%) catalyst supported on Al 2O 3 stabilised with 3% lanthanum, but at larger scale, was tested in a wood-stove. The possibility of pre-heating the catalyst during the start-up phase was studied. The tests revealed a strong decrease of the carbon monoxide and unburned hydrocarbons emissions during the start-up phase when the catalyst was pre-heated with hot air compared with no pre-heating or no catalyst.

Manganese.

Manganese is a very hard, brittle metal, which is used to increase the strength of steel alloys. Absorption from the gastrointestinal tract occurs in the divalent and tetravalent forms. Permanganates, which are strong oxidizing agents, have a +7 valence. The principal organomanganese compound is the anti-knock additive, methylcyclopentadienyl manganese tricarbonyl. Manganese is a ubiquitous constituent of the environment comprising about 0.1% of the earth's crust. For the general population, food is the most important source of manganese with daily intake ranging from 2-9 mg Mn. Combustion of gasoline containing methylcyclopentadienyl manganese tricarbonyl releases submicron particles of Mn3O4 that are potentially respirable. Biomagnification of manganese in the food chain probably does not occur. The lungs and gastrointestinal tract absorb some manganese, but the relative amounts absorbed from each site are not known. Homeostatic mechanisms limit the absorption of manganese from the gastrointestinal tract. Elimination of manganese occurs primarily by excretion into the bile. Animal studies indicate that manganese is an essential co-factor for enzymes, such as hexokinase, superoxide dismutase, and xanthine oxidase. However, no case of manganese deficiency in humans has been identified. Manganism is a central nervous system disease first described in the 1800s following exposure to high concentrations of manganese oxides. Manganese madness was the term used to describe the initial psychiatric syndrome (compulsive behavior, emotional lability, hallucinations). More commonly, these workers developed a Parkinson's-like syndrome. Currently, the risks of exposure to low concentrations of manganese in the industrial and in the environmental settings (e.g., methylcyclopentadienyl manganese tricarbonyl in gasoline) are being evaluated with regards to the development of subclinical neuropsychological changes. The American Conference of Governmental and Industrial Hygienists recently lowered the TLV-TWA for manganese compounds and inorganic manganese compounds to 0.2 mg Mn/m3.

Impact of manganese oxides on plant growth

Manganese oxides have a strong sorption capacity for metals, effectively binding and reducing bioavailability of essential trace elements to plants. This study was initiated to evaluate the impact varying proportions of manganese oxides in different "soil" media had on plant growth. Manganese oxide-coated sand, described e l sewhere(Eley and Nicholson , 1993), was employed as this was known to have a uniform c o m p o s i t i o n which had ear l ier been well-characterised. Varying proportions of the oxides (0%, 0.5%, 2%, 4%, 6%, 8%, 10% and 50% oxide by volume) were mixed with two growth media: multipurpose compost and vermiculite. Mung beans were grown from seed in each media and their growth rate monitored over 16 weeks. Mung beans were selected for study because of their rapid germination and growth rate. The metal content of the plants and manganese oxides was d e t e r m i n e d by f lame a tomic abso rp t ion spectroscopy. The deve lopment of the plants visually deteriorated with increasing concentrations of manganese oxides in the growth media. Analysis of the p lan ts g rown in the c o m p o s t showed concentrations of Fe, Zn, Mg and Ca were less than in the control samples. Potassium showed a variable b e h a v i o u r but was gene ra l ly at h igher concentrations than in the control, while Mn levels did not display any consistent trend. Plants grown in the vermiculite showed Mn and Fe concentrations greater than the control, but lower concentrations of Zn and Mg. The low levels of magnesium, an order of magnitude less than the control samples, was particularly striking. Potassium and Ca showed a variable behaviour but were generally at levels greater than in the control samples. The variations in element behaviour, with respect to the control, between growth media is in part due to the properties of the medium itself Analysis of the manganese oxides retrieved from the "soils" shows, for example, than the striking loss of Mg from the plants is probably due to take-up of Mg on the vermiculite rather than on the oxides.

ChemInform Abstract: Oxidative Coupling of Methane over Cobalt‐Magnesium and Manganese‐Magnesium Mixed Oxide Catalysts.

Abstract A series of Mn—Mg oxides and Co—Mg oxides were investigated as catalysts for the oxidative coupling of methane in a CH4/O2 co-feed, tubular reactor. The performance of the mixed oxides depended on the preparation procedure and their manganese oxide or cobalt oxide content. Physical mixtures of MnO2/MgO or Co3O4/MgO, calcined at 950°C, were selective to C2's whereas co-precipitated, calcined mixtures were amorphous and non-selective. A maximum in C2-yield of 17% was obtained at 750°C, CH4/O2=2 and 101 kPa for the manganese—magnesium oxide prepared by mixing, at a manganese oxide content equivalent to 0.8 mol-% MnO2 in MgO. The corresponding yield of the cobalt—magnesium oxide was 12% at a cobalt oxide content equivalent to 0.35% CoO in MgO. Comparison of these catalysts with a series of Li/MgO catalysts showed the latter to be unstable at the conditions investigated and the C2-yield to be dependant of the lithium compound, decreasing in the order LiCl> Li2CO3LiOH. The Li2CO3/MgO had a C2-yield of 17%. It is suggested that the C2-yield as a function of manganese or cobalt oxide content reflects the predominance of O2− or O− on the catalyst. At low cobalt or manganese oxide concentrations C2 selectivity is high and O− is expected to be dominant whereas, at higher concentrations, selectivities toward COx are high and O2− is expected to be dominant. The performance of the manganese—magnesium and cobalt—magnesium oxide measured over a range of temperatures (700–800°C), CH4/O2 ratios (1–5) and GHSV (2160–7260 ml/g cat./h) are also discussed in terms of a reaction sequence in which the majority of COx and ethane is produced via two parallel reactions and ethene is the dehydrogenation product of ethane.

Oxidative coupling of methane over cobalt—magnesium and manganese—magnesium mixed oxide catalysts

A series of Mn—Mg oxides and Co—Mg oxides were investigated as catalysts for the oxidative coupling of methane in a CH 4/O 2 co-feed, tubular reactor. The performance of the mixed oxides depended on the preparation procedure and their manganese oxide or cobalt oxide content. Physical mixtures of MnO 2/MgO or Co 3O 4/MgO, calcined at 950°C, were selective to C 2's whereas co-precipitated, calcined mixtures were amorphous and non-selective. A maximum in C 2-yield of 17% was obtained at 750°C, CH 4/O 2=2 and 101 kPa for the manganese—magnesium oxide prepared by mixing, at a manganese oxide content equivalent to 0.8 mol-% MnO 2 in MgO. The corresponding yield of the cobalt—magnesium oxide was 12% at a cobalt oxide content equivalent to 0.35% CoO in MgO. Comparison of these catalysts with a series of Li/MgO catalysts showed the latter to be unstable at the conditions investigated and the C 2-yield to be dependant of the lithium compound, decreasing in the order LiCl> Li 2CO 3LiOH. The Li 2CO 3/MgO had a C 2-yield of 17%. It is suggested that the C 2-yield as a function of manganese or cobalt oxide content reflects the predominance of O 2− or O − on the catalyst. At low cobalt or manganese oxide concentrations C 2 selectivity is high and O − is expected to be dominant whereas, at higher concentrations, selectivities toward CO x are high and O 2− is expected to be dominant. The performance of the manganese—magnesium and cobalt—magnesium oxide measured over a range of temperatures (700–800°C), CH 4/O 2 ratios (1–5) and GHSV (2160–7260 ml/g cat./h) are also discussed in terms of a reaction sequence in which the majority of CO x and ethane is produced via two parallel reactions and ethene is the dehydrogenation product of ethane.

Effect of sunlight on redox cycles of manganese in the southwestern Sargasso Sea

The cycling of manganese between soluble Mn(II) and particulate manganese oxides was investigated in the upper 750 m at a station in the southwestern Sargasso Sea. Dissolved manganese was present at a maximum concentration (4.3 ± 0.6 nM) in the surface mixed layer (0–40 m) and decreased to 0.67 ± 0.19 nM at depths of 400–750 m. Particulate manganese, on the other hand, occurred at a minimum concentration (0.034 ± 0.012 nM) in the mixed layer and increased to a maximum of 0.41–0.48 nM at depths of 120–250 m. All of the increase in particulate manganese with depth occurred within the fraction that could be reductively dissolved by 0.3 mM ascorbic acid at ambient seawater pH, indicating that the rise resulted from an increase in the concentration of manganese oxides. Oxides were undetectable in the mixed layer, but a mean of 94% of the particulate manganese appeared to be associated with oxides at depths of 80–250 m. Radiotracer ( 54MnCl 2) measurements of particulate formation rates and concomitant steady-state calculations of particulate turnover rates indicate that the low near-surface concentrations of particulate manganese resulted from both low formation rates and high turnover rates of particulate manganese. The formation of particulate manganese was sharply inhibited by sunlight, consistent with photoinhibition of manganese oxidizing microorganisms. Likewise, sunlight caused a 12-fold increase in the dissolution rate of 54Mn-labeled particulate manganese, which we attribute to photoreduction of manganese oxides. Both photo-effects appear to be important in sharply reducing the concentration of particulate manganese in near-surface seawater, and thereby minimizing the removal of manganese via particulate sinking. The resulting reduction in removal rates should be a major factor contributing to the surface maximum in manganese concentrations, which is a prominent feature of manganese profiles in much of the worlds ocean.