Presence Of MnO Research Articles

Pt/C/MnO 2 hybrid electrocatalysts for degradation mitigation in polymer electrolyte fuel cells

Pt/C/MnO 2 hybrid catalysts were prepared by a wet chemical method. Pt/C electrocatalysts were treated with manganese sulfate monohydrate (MnSO 4·H 2O) and sodium persulfate (Na 2S 2O 8) to produce MnO 2. The presence of MnO 2 was confirmed by FTIR spectroscopy. Rotating ring–disk electrode (RRDE) experiments were performed on electrodes prepared using the hybrid electrocatalysts to estimate the amount of hydrogen peroxide (H 2O 2) formed during the oxygen reduction reaction (ORR) as a function of MnO 2 content. Pt/C/MnO 2 (5% by weight of MnO 2) hybrid electrocatalysts produced 50% less hydrogen peroxide than the baseline Pt/C electrocatalyst. The hybrid electrocatalysts were used to prepare membrane electrode assemblies that were tested at 90 °C and 50% RH at open circuit with pure hydrogen as fuel and air as the oxidant. The fluoride ion concentration was measured using an ion selective electrode. The concentration of F − in the anode condensate over 24 h was found to be reduced by a factor of 3–4 when Pt/C/MnO 2 replaced Pt/C as the catalyst. Through cyclic voltammetry and RRDE kinetic studies, the lower ORR activity of the acid treated hybrid electrocatalysts was attributed to catalyst treatment with acid during MnO 2 introduction. The activity of the hybrid catalyst was improved by switching to a water-based synthesis.

Comparative study of ozone and MnO 2/O 3 effects on the elimination of TOC and COD of raw water at the Valmayor station

Two oxidation processes, O 3 and MnO 2/O 3, for the degradation of precursors of trihalomethanes(THMs), humic and fulvic acids, in aqueous solution have been investigated in this paper. Total organic carbon (TOC) and chemical oxygen demand (COD) were the parameters followed to evaluate the performance of both processes of oxidation. Comparison of their effect on the enhancement of the biodegradability was studied. While ozonation was efficient to reduce 73% COD and 67% TOC at [O 3] = 47 mg/l, COD i = 205 mg/l and TOC i = 28 mg/l in 30 minutes, ozone in the presence of MnO 2 was efficient to reduce 89% COD and 79% of TOC in 30 minutes at [O 3] = 47 mg/l, COD 0 = 180 mg/l and TOC i = 38 mg/l.

Isothermal reduction behavior of Fe 2O 3/MnO composite materials with solid carbon

Compacts of pure and 2% MnO doped iron oxide were reduced isothermally at 800–1100 °C by solid carbon. The reduction behavior was investigated using advanced quadrupole mass spectrometer. XRD and SEM analysis were used to characterize the reduced samples. The aim of this work is to clarify the reduction behavior of Fe 2O 3/MnO composite materials with solid carbon. The influence of reduction conditions on the structural characteristics of the products was extensively studied to get clear comprehension of reduction process. It was found that the reduction rate increases with temperature and decreases with the presence of MnO. The experimental measurements were used to elucidate the carbothermic reduction mechanism of iron oxide doped with MnO. The reactions proceeded in a stepwise manner and Boudouard reaction is the rate controlling step. The calculated values of activation energy revealed that solid state diffusion mechanism had a significant role in the reduction process.

MnO 2–Pt/C composite electrodes for preventing voltage reversal effects with polymer electrolyte membrane fuel cells

Water is produced at the cathode of proton-exchange membrane fuel cells (PEMFC). If water were not being removed effectively, it would accumulate at the cathode of PEMFC causing the electrode flooding. The consequence is oxygen starvation, thus increasing the concentration overpotential of the cathode. In the worst scenarios, a proton (H +) reduction reaction (PRR), instead of the oxygen reduction reaction (ORR), might occur at the cathode. Not only will this cause a cathode potential drop, but the output voltage of a single cell would likely be reversed due to oxygen starvation. This phenomenon is termed the voltage reversal effect (VRE) in this paper. To study and resolve the VRE problem, a MnO 2–Pt/C composite electrode was used to replace the conventional Pt/C electrode. The authors suggest that the electrochemical reduction of MnO 2 in the composite electrode has almost the same Nernstian potential as the ORR, which would serve as a substitute for the ORR in the case of oxygen starvation. Thus, the voltage reversal effect caused by the PRR could be avoided. Two environments, N 2- and O 2-saturated H 2SO 4, were adopted to simulate two cases, i.e., O 2 starvation and O 2 rich. It was found that MnO 2–Pt/C can prevent the voltage reversal effect to a certain extent. In a N 2-saturated 1 M H 2SO 4 solution, the current density of the Pt/C electrode made of 0.6 mg Pt cm −2 was close to 0, while for the MnO 2–Pt/C composite electrode made of 0.4 mg Pt cm −2 and 0.8 mg MnO 2 cm −2, it was as high as 10 mA cm −2. Though the current generated on the MnO 2–Pt/C composite electrode in the case of oxygen starvation is not as great as that in the case when oxygen rich, it might be high enough for some cases, such as powering a radio, hearing-aid and so like miniature devices. In an O 2-saturated 1 M H 2SO 4, the presence of MnO 2 in a MnO 2–Pt/C composite electrode primarily plays a catalytic role in the ORR. It enhances the catalytic behavior of Pt for the ORR. The impedance spectra of MnO 2–Pt/C and Pt/C electrodes were carried out for the two gases in bubbled electrolyte, which further confirmed that MnO 2 in the composite electrode does substitute for oxygen as an electron-acceptor in the case of oxygen starvation. The discharged MnO 2 can then be restored to its initial state, regardless of whether it is in oxygen rich or starved conditions.

Extent of oxidation of Cr(III) to Cr(VI) under various conditions pertaining to natural environment

Calculations show that oxidation of chromium oxide (Cr 2O 3) by oxygen and oxidation of chromium hydroxide (Cr(OH) 3) by manganese dioxide (MnO 2) are thermodynamically feasible in both aerobic and mildly anoxic environments. Experiments were carried out to determine the rate and extent of chromium oxidation under various conditions, i.e., when Cr 2O 3 was heated in the presence of oxygen, when Cr(OH) 3 and MnO 2 mixtures were suspended in aerobic or anoxic aqueous media at various pH values, when Cr(OH) 3 and MnO 2 mixtures interacted in moist aerobic conditions and when chromium assumed to be Cr(OH) 3 and manganese assumed to be MnO 2 interacted in the presence of competing electron donors/acceptors, as is the case in chromium-contaminated sludge. Results indicate that trivalent chromium in Cr 2O 3 could be readily converted to hexavalent chromium at a temperature range of 200–300 °C, with conversion rates of up to 50% in 12 h. In aqueous media, Cr(OH) 3 was slowly converted to dissolved Cr(VI) in the presence of MnO 2, both in aerobic and anoxic conditions, with conversion rates of up to 1% in 60 days. In moist aerobic conditions and in the presence of MnO 2, Cr(OH) 3 slowly converted to hexavalent chromium, with up to 0.05% conversion observed in 90 days. Chromium oxidation also occurred in sludge samples, especially under aerobic conditions. However, such transformation was found to be transitory, with the Cr(VI) formed being ultimately reduced back to Cr(III) due to the presence of various reducing agents in the sludge. Nevertheless since up to 17% conversion of Cr(III) to Cr(VI) occurred in sludge under aerobic conditions by 30 days, there is real danger under field conditions of spreading Cr(VI) pollution due to possible intervening rainfall, runoff and percolation.

Adsorption of REE(III)-humate complexes onto MnO 2: Experimental evidence for cerium anomaly and lanthanide tetrad effect suppression

Experiments were conducted to evaluate the impact of organic complexation on the development of Ce anomalies and the lanthanide tetrad effect during the adsorption of rare-earth elements (REE) onto MnO 2. Two types of aqueous solutions—NaCl and NaNO 3—were tested at pH 5 and 7.5. Time-series experiments indicate that a steady-state is reached within less than 10 h when REE occur as free inorganic species, whereas steady state is not reached before 10 d when REE occur as REE-humate complexes. The distribution coefficients (K d REE) between suspended MnO 2 and solution show no or only very weak positive Ce anomaly or lanthanide tetrad effect when REE occur as humate complexes, unlike the results obtained in experiments with REE occurring as free inorganic species. Monitoring of dissolved organic carbon (DOC) concentrations show that log K d REE organic /K d DOC ratios are close to 1.0, implying that the REE and humate remain bound to each other upon adsorption. Most likely, the Ce anomaly reduction/suppression in the organic experiments arises from a combination of two processes: (i) inability of MnO 2 to oxidize Ce(III) because of shielding of MnO 2 surfaces by humate molecules and (ii) Ce(IV) cannot be preferentially removed from solution due to quantitative complexation of the REE by organic matter. We suggest that the lack of lanthanide tetrad effect arises because the adsorption of REE-humate complexes onto MnO 2 occurs dominantly via the humate side of the complexes (anionic adsorption), thereby preventing expression of the differences in Racah parameters for 4f electron repulsion between REE and the oxide surface. The results presented here explain why, despite the development of strongly oxidizing conditions and the presence of MnO 2 in the aquifer, no (or insignificant) negative Ce anomalies are observed in organic-rich waters. The present study demonstrates experimentally that the Ce anomaly cannot be used as a reliable proxy of redox conditions in organic-rich waters or in precipitates formed at equilibrium with organic-rich waters.

Effect of pH on MnOx/GAC catalyzed ozonation for degradation of nitrobenzene

The effect of pH on MnO(x)/GAC heterogeneous catalytic ozonation was investigated. Nitrobenzene was used as a model refractory organic pollutant. It was found that in MnO(x)/GAC catalytic ozonation, the degradation efficiency of nitrobenzene was higher under low pH conditions (pH 2.74-3.52) than that under high pH conditions (pH 6.72-9.61). This result was different from the case of ozonation alone, in which higher pH had positive effect on the degradation of nitrobenzene due to the formation of hydroxyl radical. In the presence of MnO(x)/GAC catalyst, ozone decomposition was accelerated, and higher pH condition favored ozone decomposition. It was assumed that hydroxyl radicals might not be the dominating active species in the catalytic oxidation, for the presence of t-butanol did not have any influence on MnO(x)/GAC heterogeneous catalytic ozonation. Adsorption of organic micropollutants on MnO(x)/GAC catalyst was an important step and would have direct influence on the effectiveness of catalytic oxidation. It was assumed that the organic pollutants might be further decomposed on the surface of catalyst.

Synthesis of Biologically Active 5‐Benzopyranylpyridines and Triazolopyridines.

AbstractFor Abstract see ChemInform Abstract in Full Text.

γ-Radiolytic desulphurisation of some high-sulphur Indian coals catalytically accelerated by MnO 2

γ-Radiolysis of acidic aqueous coal slurries is a novel and effective method for the simultaneous oxidative desulphurisation and demineralisation of high-sulphur coals. This method is capable to selectively remove the inorganic and organic forms of sulphur simultaneously through the in situ-generated H 2O 2 and other radiolytic products. In effect, there is neither any appreciable degradation of coal matrix nor any loss in the caking property and volatile matter content of the coals after the removal of sulphur. However, significant removals of sulphur and mineral matter are effected at rather high γ-dose (175×10 4 Gy or so). Therefore, for the process to be economically viable and commercially adaptable, the applied γ-dose needs to be somehow substantially brought down, at which the same level of desulphurisation could be achieved. Catalytically, accelerating the radiolysis process is one such possibility to effect the desulphurisation step at a low γ-dose. Reported in this paper are the results of investigations on the desulphurisation and demineralisation of high-sulphur (sulphur content in the range 3–5.5%) Churphy, Chalang and Bapung coals of Meghalaya by γ-radiolytic process catalysed by MnO 2. The maximum removal of total sulphur (15.6%, 30.0% and 29.8%) at 30×10 4 Gy in the presence of MnO 2 and the simultaneous removal of mineral matter (20.0% and 18.5% from Churphy and Chalang coals at 30×10 4 Gy and 12.0% from Bapung coal at 45×10 4 Gy) are at par with removals at 175×10 4 Gy without MnO 2, which has been attributed to MnO 2 catalytically accelerating the radiolytic process via the formation of highly reactive MnO under the action of γ-rays. All the other features of non-catalysed radiolytic desulphurisation such as stabilisation of the slurry and coal not becoming radioactive during irradiation, increase in the heating value, improvement in the caking property, no appreciable degradation of coal matrix after removal of sulphur from the coals remain the same.

Anaerobic sulfide oxidation and stable isotope fractionation associated with bacterial sulfur disproportionation in the presence of MnO 2

The sulfur and oxygen isotope effects associated with anaerobic bacterial disproportionation of elemental sulfur by a pure culture ( Desulfocapsa thiozymogenes) and an enrichment culture were investigated experimentally in the presence of synthetic Mn(IV)oxides. During bacterial disproportionation, 34S/ 32S were fractionated in dissolved sulfate compared to elemental sulfur by −0.6 to +2.0‰ ( D. thiozymogenes) and −0.2 to +1.1‰ (enrichment culture) at cellular sulfur disproportionation rates of 10 −16 mol S°/cell/h and 10 −17 mol S°/cell/h, respectively. The measured sulfur isotope effects are much smaller than those observed previously for the same cultures in the presence of Fe(III) and Fe(II) compounds, indicating that microbial isotope fractionation was superimposed by the chemical re-oxidation of hydrogen sulfide by MnO 2 to sulfate. Significant re-oxidation of H 2S to sulfate was additionally confirmed by the oxygen isotopic composition of sulfate, which was enriched in 18O compared to water by +8 to +12‰. These new experimental results imply that the overall influence of bacterial disproportionation on stable isotope partitioning in natural surface sediments depends on the proportion and relative recycling rates of reactive Fe(III) to Mn(IV)(oxyhydr)oxides.

Oxidation of pyrite and iron sulfide by manganese dioxide in marine sediments

Oxidation of pyrite (FeS 2) under anaerobic conditions in marine sediments is experimentally shown for the first time. In slurry experiments with 55FeS 2 and a MnO 2 rich marine sediment an oxidation of 55FeS 2 was detected which decreased with depth and decreasing concentration of MnO 2 in the sediment. FeS 2 and iron sulfide (FeS) were oxidized chemically at pH 8 by MnO 2 but not by nitrate or amorphic Fe(III) oxide. Elemental sulfur and sulfate were the only products of FeS oxidation, whereas FeS 2 was oxidized to a variety of sulfur compounds, mainly sulfate plus intermediates such as thiosulfate, trithionate, tetrathionate, and pentathionate. Thiosulfate was oxidized by MnO 2 to tetrathionate while other intermediates were oxidized to sulfate. The reaction products indicate that FeS 2 was oxidized via the “Thiosulfate-mechanism” and FeS via the “Polysulfide-mechanism” (Schippers and Sand, 1999). The processes are summarized by the overall equations: (1) FeS 2+7.5 MnO 2+11 H +→Fe(OH) 3+2 SO 4 2−+7.5 Mn 2++4 H 2O (2) FeS+1.5 MnO 2+3 H +→Fe(OH) 3+S O+1.5 Mn 2+ For FeS 2 oxidation the reaction rates related to the mineral surface area were 1.02 and 1.12 nmol m −2 s −1 for total dissolved S and total dissolved Fe, respectively. Since these values are in the same range as previously published rates for the oxidation of FeS 2 by Fe(III), and since Fe(III) is a well-known oxidant for FeS 2 even at circumneutral pH, Fe(III) is assumed also to be the oxidant for FeS and FeS 2 in the presence of MnO 2. At the iron sulfide surface, Fe(III) is reduced to Fe(II) which is reoxidized to Fe(III) by MnO 2. Thus, an Fe(II)/Fe(III) shuttle should transport electrons between the surfaces of the two solid compounds.

Kinetics of the arsenite oxidation in seepage water from a tin mill tailings pond

The kinetic of the oxidation of trivalent arsenic was investigated in synthetic as well as in natural samples of a tin mill seepage water. The influence of ferric ions and solid MnO 2 on the process was studied. To determine the time dependence of the concentrations of the arsenic species, a series of samples were taken sequentially and analysed by coupling of ionchromatographic separation and ICP-MS detection. To investigate the naturally occurring oxidation reaction, original seepage water samples were filtered and spiked with As(III) (1 mg l −1) and Fe(II) (10 mg l −1) and shaken providing intensive contact with the air. Additional synthetic samples buffered with carbonate were used in similar experiments to simplify the system. The reaction was incomplete in the presence of excess of iron for both types of samples. The oxidation of As(III) was complete within 8 h in the presence of MnO 2 (10 mg), but there was a difference in oxidation rates between the natural and the synthetic samples. The results are discussed with respect to the redox potentials and equilibrium constants.

Charpy V-notch properties and microstructures of narrow gap ferritic welds of a quenched and tempered steel plate

Multipass welds of quenched and tempered 50-mm-thick steel plate have been deposited by a single wire narrow gap process using both gas metal arc welding (GMAW) and submerged arc welding (SAW). Of the five welds, two reported much lower Charpy V-notch (CVN) values when tested at −20 °C. The CVN toughness did not correlate with either the welding process or whether the power source was pulsed or nonpulsed. The only difference in the ferritic microstructure between the two welds of low Charpy values and the three of high values was the percentage of acicular ferrite. There was no effect of the percentage of as-deposited reheated zones intersected by the Charpy notch or the microhardness of the intercellular-dendritic regions. In all welds, austenite was the microconstituent between the ferrite laths. The percentage of acicular ferrite correlated with the presence of MnO, TiO2, γ Al2O3, or MnO. Al2O3 as the predominant crystalline compound in the oxide inclusions. In turn, the crystalline compound depended on the aluminum-to-titanium ratio in both the weld deposits and the oxide inclusions. In addition to the presence of less acicular ferrite, the two welds that showed lower Charpy values also reported more oxide inclusions greater than 1 µm in diameter. The combination of more oxide inclusions greater than 1 µm and less acicular ferrite is considered to be the explanation for the lower Charpy values.

Novel Visible and Ultraviolet Light Photogeneration of Hydroxyl Radicals by 2‐Methyl‐4‐nitro‐quinoline‐N‐oxide (MNO) and 4, 4′‐Dinitro‐(2, 2′) bipyridinyl‐N, N′‐dioxide (DBD)

Chemicals that upon absorption of light generate hydroxyl radicals (.OH), free of other damaging species under physiological conditions, are useful tools for the study of the biological effects of .OH radical and for its utilization for analytical purposes. We report the novel property of 2-methyl-4-nitro-quinoline-N-oxide (MNO) and 4,4'-dinitro-(2,2')bipyridinyl-N,N'-dioxide (DBD) to act as photogenerators of .OH with UV and visible light. Upon irradiation with 360-400 nm light MNO and DBD generate free radicals that convert coumarin carboxylic acid (CCA) to fluorescent 7-OH-CCA; the .OH radical scavengers dimethylsulfoxide (DMSO) and ethanol eliminate the induction of 7-OH-CCA fluorescence. Upon 400 nm illumination in the presence of MNO, supercoiled plasmid DNA is converted to circular and strand breakage is significantly reduced in the presence of DMSO and completely absent in the absence of MNO. The conversion of CCA to 7-OH-CCA and of supercoiled plasmid to circular DNA are also observed in the absence of oxygen. Taken together, these data indicate that MNO and DBD constitute novel .OH-generating compounds. Because currently known .OH-photogenerating compounds require UV illumination (< 360 nm) that also damages DNA and cells directly, the property of MNO to generate .OH upon 400 nm illumination is advantageous when studies on cells, DNA and other biomolecules are conducted.

Electronic and steric effects of various silyl groups in radical addition reactions

Abstract The ligands on a silicon atom in allylsilanes were found to influence the efficiency of their reaction with ketones in the presence of MnO 2 . An electron-donating group on silicon provided a promoting effect, yet the steric effect of a bulky silyl group retarded the addition process.

A Novel Concept for the Mechanism of Higher Oxygenate Formation from Synthesis Gas over MnO-Promoted Rhodium Catalysts

Based on data from zeolite-supported catalysts, a new model is proposed for the formation of higher oxygenates from syngas over MnO-promoted Rh. Oxygenate precursors, CxHyOz, are formed at MnO sites in close proximity to the Rh-MnO interface. The role of Rh is the formation and delivery of CHxgroups and H atoms. FTIR indicates that theCxHyOz complex is probably a surface acetate. Results from ethylene hydroformylation tests at relatively low temperatures, where CO dissociation does not occur, show that the presence of MnO in the catalyst does not enhance the abilityof Rh to catalyze CO insertion. At higher temperatures though, where CO dissociation occurs, higher oxygenates are formed only in negligible amounts over unpromoted Rh. The role of MnO in enhancing the formation of higher oxygenates was tested using CHCl3 as a source ofCHx groups instead of Rh. Formation of the oxygenate precursor CxHyOz from the surface reaction between CHCl3, CO, and H2 is detected by FTIR on MnOin the absence of Rh. The same complex is formed from the same reaction over cosupported Rh/MnO and the physical mixture Rh + MnO. However, its hydrogenation to higher oxygenates, occursonly over Rh/MnO, where Rh and MnO particles are in close contact. Furthermore, this hydrogenation is apparently confined to those acetate groups located on MnO sitesat the Rh-MnO interface. Summarizing, the MnO promoter basically behaves as a cocatalyst; the formation of higher oxygenates from syngas is another example of bifunctional catalysis with essential steps taking place at the interface of both catalytic functions.

Magnetic properties of Cr and Mn powders (abstract)

Mn and Cr powders were produced from electrolytic Mn and Cr by ball milling in a stainless steel container with carbon steel balls. The milling time, t, varied from 5 min to 8 h. Structures were investigated by x-ray and electron microscopy. Chemical compositions of samples were checked by flame atomic absorption spectrometry. The magnetization was measured by induction method in a pulsed magnetic field up to 10 T. The main part of Mn and Cr powder volume was occupied by α-Mn and b.c.c. Cr, respectively. Diffraction peaks became vaster and more asymmetric with increasing t due to the onset of defects of the structure. The presence of MnO was observed in the Mn sample after 8 h of milling. The size of Mn and Cr particles over same critical t (for chromium t=100 min) was no more than 1 mm. A noticeable Fe content, which increases at higher t, was observed. The Mössbauer spectra of Cr and Mn samples showed the lines of α-Fe and γ-Fe. High values of saturation magnetization, σ, up to 5.4 emu/g, and susceptibility and existence of the hysteresis in low fields at temperatures up to 360 K, indicate ferromagnetic ordering of the samples. Within the range of 78–360 K σ only slightly depends on temperature, but noticeably grows with increasing t at fixed temperature in Cr powders, remaining practically constant in Mn powders. No correlation could be observed between Fe content and σ : the latter remained the same in Mn with Fe concentration increasing, but in Cr, as Fe concentration increased sevenfold, it grew by four times. Spontaneous magnetization per mass unit of Fe, σ, was sufficiently lower than that of pure α-Fe (220 emu/g). The obtained values of σ correspond neither to Fe solid solution nor to pure Cr or Mn. Elucidation of the obtained results can be done both by the presence of α-Fe particles and by variation of exchange interactions caused by sample defects. A noticeable difference of σ values from those properties of bulk α-Fe can be explained by γ-Fe availability and grinding of particles being smaller than single domain sizes.

A new route to 6-substituted 2,3-diaminopyridines

2,3-Diaminopyridine reacts with cyclohexanone to form dihydro-4-azabenzimidazole-2-spirocyclohexane. Reaction of this intermediate with a variety of nucleophiles (e.g., water, phenylmercaptan, ethanol, dimethylamine, and diethylmalonate) in the presence of MnO 2 results in addition to the 5-position. Subsequent acidic hydrogenation affords 6-substituted-2,3-diaminopyridines, key synthons for the synthesis of bicyclic heterocycles.

A derivatographic study of the thermal degradation of tetrabutyl ammonium perchlorate

This article presents the results of non-isothermal analysis, under static air and dynamic argon atmospheres, of tetrabutyl ammonium perchlorate (TBAP), alone and in the presence of MnO 2 as a thermal catalyst. Thermogastitrimetry and mass spectrometry were used to identify some of the gaseous products. The effects of the four butyl groups on the thermally excited ammonium nitrogen atom are discussed. The thermal stabilities of TBAP and the parent molecule, ammonium perchlorate, are compared. The effects of using different sample weights, atmospheres and crucible materials were tested.

DTA studies on preparation of MnSO4 by reacting pyrite and pyrolusite at high temperatures

The preparation of MnSO4 by reacting pyrolusite at high temperatures with SO2 generated from pyrite was followed by DTA, and the process conditions were optimized to fix the minimum time and temperature of reaction required to obtain the maximum yield of pure MnSO4 from stoichiometric amounts of reactants in a natural draught of air. The presence of MnO and Fe3O4 in the reaction products, detected by DTA, indicates that the SO2 is initially oxidized to SO3 by reducing MnO2, Mn2O3 and Fe2O3 to MnO and Fe3O4. SO3 finally attacks MnO to form MnSO4. When an intimate stoichiometric blend of pyrite and pyrolusite is heated at temperatures ranging from 873 K to 973 K for 3 hrs, about 93% of the Mn is converted to ironfree MnSO4.