Pyrolusite, reduction

Manganese is the third most abundant transition metal, and is widely distributed in the earth s crust. The most important ore is pyrolusite, manganese(IV) oxide. Reduction of this ore by heating with aluminium gives an explosive reaction, and the oxide Mn304 must be used to obtain the metal. The latter is purified by distillation in vacuo just above its melting point (1517 K) the pure metal can also he obtained by electrolysis of aqueous manganese(II) sulphate. 

Most manganese today is obtained from ores found in Russia, Brazil, Australia, Republic of S. Africa, Gabon, and India. Pyrolusite and rhodochrosite are among the most common manganese minerals. The metal is obtained by reduction of the oxide with sodium, magnesium, aluminum, or by elctrolysis. 

Manganese Mn, at wt 54.94, brittle, silvery metal, mp 1245°, bp 2097°, d 7,44g/cc, Mohs hardness 5 decomps in w, readily dissolved in dil mineral acids. Usually associated with Fe ores in sub-marginal concns. Important ores of Mn are pyrolusite, manganite, psilomelane rhodochrosite. Prepd by reduction of the oxide with Al or C. Pure Mn is obtained electrolyti-cally from sulfate or chloride sain. It is used, in powd form, in the manuf of delay powds and in some pyrotechnic mixts. The requirements of the USA Armed Forces are covered by... 

Place 100 g. of finely powdered pyrolusite, Mn02, in a Hessian crucible and heat it in a gas furnace to convert it into Mn304 (the reaction with Mn02 is too violent). Weigh the Mn304 thus obtained and mix it with a little less than the weight of granulated aluminum required for its reduction ... 

Manganese Pyrolusite (Mn02) Reduction of oxide by carbon or aluminum Manufacturing alloys with iron and other metals... 

Manganese dioxide, a grey to black solid, occurs in ores such as pyrolusite, where it is usually nonstoichiometric. When made by the action of 02 on Mn at a high temperature, it has the rutile structure found for many other oxides M02 (e.g., those of Ru, Mo, W, Re, Os, Ir, and Rh). However, as normally made by heating Mn(N03)2-6H20 in air ( 530°C), it is nonstoichiometric. A hydrated form is obtained by reduction of aqueous KMn04 in basic solution. Manganese(IV) occurs in a number of mixed oxides. 

Lovley and Phillips, 1986). Minerals such as ferrihydrite and lepidocrocite (y-FeOOH) are generally reduced more rapidly than relatively stable minerals such as goethite and hematite (Postma, 1993). Amorphous manganese oxides such as vernadite are more easily reduced than strongly crystalline forms such as pyrolusite, but the overall influence of crystallinity on reduction kinetics appears to be weaker for manganese and iron oxides (Burdige et ai, 1992). 

Manganese(Il) oxide is manufactured by the reduction of naturally occurring mangane.se(lV) oxide-containing ttres (e.g. pyrolusite) with carbon or methane ... 

The Mn ion in pyrolusite (Mn02) is rather inert in oxidation reactions, evidently because the one-electron Mn — Mn reduction step is not a very favorable reaction. 

Manganese is produced by carbon reduction of pyrolusite, Mn02, which occurs in two stages Mn02—>MnO—>Mn. Determine the lowest practicable temperature for the second stage of the process. Is the product easily separable from the reaction mixture ... 

A 0.200-g sample of pyrolusite is analyzed for manganese content as follows. Add 50.0 mL of a 0.100 M solution of ferrous ammonium sulfate to reduce the Mn02 to Mn. After reduction is complete, the excess ferrous ion is titrated in acid solution with 0.0200 M KMn04, requiring 15.0 mL. Calculate the percent manganese in the sample as Mn304 (only part or none of the manganese may exist in this form, but we can make the calculations on the assumption that it does). 

Occurs chiefly in pyrolusite, MnOi, hausmanite, MnsO<, brau-nite, MnsOs, and manganite, MnjOs, HjO. A hard, grayish, brittle metal fusible with difficulty obtained by reduction of its oxids by C at a white heat. It is not readily oxidized by cold, dry air but is superficially oxidized when heated. It decomposes HsO, liberating H and dissolves in dilute acids. 

Surface passivating layers are further discussed by White and Peterson (55) in the oxidation of magnetite by Cr and by Fendorf (29) in the reduction of pyrolusite by Co -EDTA complexes. In both cases, surface passivation removes the bulk mineral from further reaction with the solution and significantly reduces the redox capacity of the mineral. 

Our objectives for this research were to (1) use XANES spectroscopy to quantify subtle changes in solid-state geochemistry after hydrodynamic flow (2) determine if geochemical reduction of structural Mn(IV) or Fe(III) in oxide minerals occurred by surface-associated Co(II)EDTA (3) identify the source of Co(II) oxidation inhibition in pyrolusite and ferrihydrite media. 

---