Manganese, hydrated oxides

There are approximately 250 known manganese minerals. The primary ores which typically have a Mn content >35%, usually occur as oxides or hydrated oxides, or to a lesser extent as siUcates or carbonates. Table 5 Hsts the manganese-containing minerals of economic significance (10). Battery-grade manganese dioxide ores are composed predominately of nsutite, cryptomelane, and todorokite. 

The Mn ion is so unstable that it scarcely exists in aqueous solution. In acidic aqueous solution, manganic compounds readily disproportionate to form Mn ions and hydrated manganese(IV) oxide, Mn02 2H20 in basic solution these compounds hydroly2e to hydrous manganese(III) oxide, MnO(OH). Sulfuric acid concentrations of about 400 450 g/L are required to stabilize the noncomplexed Mn ion in aqueous solutions. 

Manganese Hydrate. . Manganic Oxide. . Manganoua Oxide. . . ... 

About 90% of manganese ore is used in steel smelting. Although there are more than 300 manganiferous minerals, the common ore minerals are largely mixtures of manganese oxides and hydrated oxides. The usual field terms are psilomelane for a hard massive mixture of oxide minerals, pyrolusite for a soft black earthy mixture, and wad for impure, brown earthy oxides and hydrated oxides. LIBS sorting may be effective in this case (Fig. 8.11). 

After filtration, addition of sodium sulphide to the clear solution effects the precipitation of the three metals, cobalt, nickel, and manganese, as sulphides. Digestion with the calculated quantity of ferric chloride oxidises the manganese sulphide to sulphate, which passes into solution. The residue consists of cobalt and nickel sulphides, which are washed and converted into their soluble sulphates by roasting. The sulphates are extracted with water, and converted into chlorides by addition of calcium chloride solution. Their separation is effected g.s follows The requisite fraction of the chloride solution is precipitated with milk of lime, and the insoluble hydroxides of nickel and cobalt thus obtained are oxidised to the black hydroxides by treatment with chlorine. The. washed precipitate is then introduced into the remainder of the chloride solution, and the whole is well stirred and heated, when the black hydrated oxide of nickel passes, into solution, displacing tlm Remainder of. the cobalt from the solution, into. the precipitate.. The final product is thus a suspension of hydrated peroxide.of cobalt,in p. solution of nickel chloride, from which idle cobalt precipitate is removed by filtration, washed, and ignited, to the black oxide. 

One can see that decomposition temperatures of these compounds are within temperature range 40-600°C. Some compounds, such as monohydrate of lithium hydroxide (40°C), hydrated titanium dioxide (60°C), iron hydroxide (100°C), manganese (145°C) and cobalt (150°C) hydroxides, tungsten acid (180°C), etc., start to release water at relatively low temperatures. Other compounds decompose at a temperature above 200°C. No correlation between formation enthalpy and thermal stability of hydroxides and hydrated oxides is observed. 

Oxidation by potassium permanganate is usually carried out in acetic or sulfuric acid solution. Isolation of the sulfone must include separation from the precipitate of manganese(iv) oxide hydrate, which, in the case of sparingly soluble sulfones, is effected by reduction of this precipitate by just sufficient sodium hydrogen sulfite solution or by sulfur dioxide soluble sulfones can be isolated by addition of water after filtration from the hydrated manganese oxide or by acidification and extraction with ether. 

Oxidation of Mn(II) and Mn(III) up to Mn(IV) accompanied by precipitation of hydrated oxides is an important process in the course of manganese removal from waters. In comparison with Fe(II), Mn(II) is more resistant to oxidation. Oxidation with dissolved oxygen proceeds more markedly only at pH > 9. On the contrary, it is easier to achieve reduction of Mn(III) or Mn(IV) to Mn and thus also dissolution and release of manganese from the sediments into the liquid media under conditions where the reduction of Fe(IIl) to Fe(II) does not yet take place. 

This kinetic equation involves an additive member containing the product of oxidation (in contrast to Fe(II) oxidation). It is an autocatalytic reaction. Therefore, when removing manganese from water, employing so-called manganese filters, it is first necessary to form a layer of higher hydrated oxides of manganese on the carrier, which is usually sand. 

The peptization capabilities of polyphosphates depend on their sorption on aluminosilicates and colloidal particles of hydrated oxides of iron, aluminium and manganese. In practice, this causes problems in water treatment by coagulation when already rather low concentrations of polyphosphates can cause improper agglomeration of colloidal particles into sedimentable floccules. 

The technique for the removal of iron and manganese during water treatment employs the oxidation of bivalent well-soluble forms to multivalent low-soluble hydrated oxides, which can be removed from water either by sedimentation or filtration. Oxidizing agents in this case are atmospheric oxygen, chlorine, potassium permanganate, ozone and chlorine dioxide. 

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