Introduction
Manganese dioxide is the inorganic compound with the formula MnO
2. This blackish or brown solid occurs naturally as the mineral pyrolusite, which is the main ore of manganese and a component of manganese nodules. The principal use for MnO
2 is for dry-cell batteries, such as the alkaline battery and the zinc–carbon battery.[4] MnO
2 is also used as a pigment and as a precursor to other manganese compounds, such as KMnO
4. It is used as a reagent in organic synthesis, for example, for the oxidation of allylic alcohols. MnO
2 has an α-polymorph that can incorporate a variety of atoms (as well as water molecules) in the “tunnels” or “channels” between the manganese oxide octahedra. There is considerable interest in α-MnO
2 as a possible cathode for lithium-ion batteries. Manganese oxides mainly include manganese monoxide (MnO), manganese dioxide (MnO2), manganese trioxide (Mn2O3), manganese tetroxide (Mn3O4), and so on. Manganese dioxide, an inorganic compound with chemical formula MnO2, is a black amorphous powder or black crystalline powder, which is insoluble in water.
Manganese dioxide is used in the preparation of manganese salt, also used as oxidant, rust remover, and catalyst. Manganese dioxide nanomaterials include a variety of morphologies such as monodisperse nanoparticles, nanoflowers, nanofibers, nanowires, and nanorods. Manganese dioxide has become one of the alternative materials to replace precious metals as the electrode material of supercapacitors due to its cheap, easy to obtain, and environmentally friendly characteristics. Manganese dioxide with a high specific surface area is a novel pseudocapacitor material with a low price and similar electrochemical properties to Ruthenium oxide [1].
1. Structure
Several polymorphs of MnO
2 are claimed, as well as a hydrated form. Like many other dioxides, MnO
2 crystallizes in the rutile crystal structure (this polymorph is called pyrolusite or β-MnO
2), with three-coordinate oxide anions and octahedral metal centres.[4] MnO
2 is characteristically nonstoichiometric, being deficient in oxygen. The complicated solid-state chemistry of this material is relevant to the lore of “freshly prepared” MnO
2 in organic synthesis.[7] The α-polymorph of MnO
2 has a very open structure with “channels”, which can accommodate metal ions such as silver or barium. α-MnO
2 is often called hollandite, after a closely related mineral.
- Production
Naturally occurring manganese dioxide contains impurities and a considerable amount of manganese(III) oxide. Production of batteries and ferrite (two of the primary uses of manganese dioxide) requires high purity manganese dioxide. Batteries require “electrolytic manganese dioxide” while ferrites require “chemical manganese dioxide”
Chemical manganese dioxideOne method starts with natural manganese dioxide and converts it using dinitrogen tetroxide and water to a manganese(II) nitrate solution. Evaporation of the water leaves the crystalline nitrate salt. At temperatures of 400 °C, the salt decomposes, releasing N
2O
4 and leaving a residue of purified manganese dioxide.[8] These two steps can be summarized as:
MnO
2 + N
2O
4 ⇌ Mn(NO
3)
2
In another process, manganese dioxide is carbothermically reduced to manganese(II) oxide which is dissolved in sulfuric acid. The filtered solution is treated with ammonium carbonate to precipitate MnCO
3. The carbonate is calcined in air to give a mixture of manganese(II) and manganese(IV) oxides. To complete the process, a suspension of this material in sulfuric acid is treated with sodium chlorate. Chloric acid, which forms in situ, converts any Mn(III) and Mn(II) oxides to the dioxide, releasing chlorine as a by-product.[8]
Lastly, the action of potassium permanganate over manganese sulfate crystals produces the desired oxide.[9]
2 KMnO
4 + 3 MnSO
4 + 2 H
2O→ 5 MnO
2 + K
2SO
4 + 2 H
2SO
4
3. Electrolytic manganese dioxide
Electrolytic manganese dioxide (EMD) is used in zinc–carbon batteries together with zinc chloride and ammonium chloride. EMD is commonly used in zinc manganese dioxide rechargeable alkaline (Zn RAM) cells also. For these applications, purity is extremely important. EMD is produced in a similar fashion as electrolytic tough pitch (ETP) copper: The manganese dioxide is dissolved in sulfuric acid (sometimes mixed with manganese sulfate) and subjected to a current between two electrodes. The MnO2 dissolves, enters solution as the sulfate, and is deposited on the anode.[10]
4. Primary Batteries – Aqueous Systems | Leclanché And Zinc–Carbon
1. Manganese Dioxide
The type of manganese dioxide (MnO2) and its quantity used in dry cells are mainly responsible for cell capacity. Performance characteristics depend on individual crystal structure, varying degrees of hydration, and the activity of the manganese dioxide. Manganese dioxide potentials are additionally affected by the pH of the electrolyte.
Most zinc–carbon batteries are cathode limited.
Four different types of manganese dioxide are applied in dry cells: (NMD alpha- and beta-structure), activated manganese dioxide (AMD), chemically synthesized manganese dioxide (CMD, delta-structure), and electrolytic manganese dioxide (EMD, gamma-structure). Activated manganese dioxide is prepared by chemical treatment of natural ore (roasting, sulfuric acid treatment).
The CMD type may be obtained either as a by-product of an oxidation process with potassium permanganate or by thermal decomposition of other manganese compounds followed by oxidation. Electrolytic manganese dioxide is obtained by anodic oxidation of manganese sulfate in hot sulfuric acid. Although more expensive, EMD has the advantage of yielding higher cell capacity with improved rate capability (for heavy or industrial applications) and its polarization is significantly lower compared to other types.
2. Oxidation
Oxidation with Manganese Dioxide
Although manganese dioxide (MnO2) is a common form of Mn(IV), it is rather insoluble in most organic solvents. Manganese dioxide is the usual end-product of permanganate oxidations in basic solution (sec. 3.5.A). The reduction potential of MnO2 is 1.208 volts for the following reaction.17
MnO2+4H++2e-→Mn2++2H2O1.208V
Manganese dioxide is capable of oxidizing alcohols to ketones or aldehydes, and the reaction proceeds via a radical intermediate (see below), producing MnO (which is Mn2+) as the by- product. Manganese dioxide oxidizes primary and secondary alcohols to the aldehyde or ketone, respectively, in neutral media.156 Ball, et al discovered this reaction, by precipitating manganese dioxide and then converting vitamin A (104) to retinal (105) in 80% yield.157
5. Manganese oxide minerals: Crystal structures and economic and environmental significance
1. Abstract
Manganese oxide minerals have been used for thousands of years—by the ancients for pigments and to clarify glass, and today as ores of Mn metal, catalysts, and battery material. More than 30 Mn oxide minerals occur in a wide variety of geological settings. They are major components of Mn nodules that pave huge areas of the ocean floor and bottoms of many fresh-water lakes. Mn oxide minerals are ubiquitous in soils and sediments and participate in a variety of chemical reactions that affect groundwater and bulk soil composition.
Their typical occurrence as fine-grained mixtures makes it difficult to study their atomic structures and crystal chemistries. In recent years, however, investigations using transmission electron microscopy and powder x-ray and neutron diffraction methods have provided important new insights into the structures and properties of these materials. The crystal structures for todorokite and birnessite, two of the more common Mn oxide minerals in terrestrial deposits and ocean nodules, were determined by using powder x-ray diffraction data and the Rietveld refinement method.
Because of the large tunnels in todorokite and related structures there is considerable interest in the use of these materials and synthetic analogues as catalysts and cation exchange agents. Birnessite-group minerals have layer structures and readily undergo oxidation reduction and cation-exchange reactions and play a major role in controlling groundwater chemistry.
2. Ocean Mn Nodules
The most extensive deposition of Mn oxides today occurs in the oceans as nodules, microconcretions, coatings, and crusts (7). Marine Mn nodules were first discovered in 1873 during the voyage of the HMS Challenger (8). Since then, Mn nodules have been found at almost all depths and latitudes in all of the world’s oceans and seas (7); it has been estimated, for example, that they cover about 10–30% of the deep Pacific floor (9). Ocean Mn nodules typically are brown-black and subspherical-botroyoidal and consist of concentric layers of primarily Mn and iron oxide minerals. Other minerals commonly found in the nodules include: clay minerals, quartz, apatite, biotite, and feldspars (10). Most Mn nodules have formed around central nuclei that may be carbonate mineral fragments, pumice shards, animal remains, coral fragments, etc. (11).
The nodules range from 0.5 to 25 cm in diameter, with an ocean-wide average of about 4 cm (11). Marine Mn oxide crusts and nodules concentrate at the sediment-water interface (12) but locally are distributed to a depth of 3 or 4 m (13). The nodules are most abundant in oxygenated environments with low sedimentation rates and reach their greatest concentration in deep-water at or below the calcium carbonate compensation depth (11). Accumulation rates range from 0.3 to 1,000 mm/yr in near-shore environments to about 1 cm/million yr in the deep ocean (14, 15). The source of the Mn is thought to be continental runoff and hydrothermal and volcanic activity at midocean spreading centers (16, 17).
Research on the complex mineralogy of the Fe and Mn oxides in ocean Mn nodules has been hampered by the fact that the minerals typically occur as thin layers of fine-grained, poorly crystalline mixtures. Previous studies of the mineralogy of ocean nodules concluded that the dominant Mn oxide phases are birnessite (7 Å manganate), todorokite (10 Å manganate), and δ-MnO2 or vernadite (18). Both birnessite and todorokite commonly are found in the same nodule, but birnessite tends to predominate in nodules from topographic highs such as seamounts and ridges, and todorokite is more common in slightly more reducing near-shore and abyssal environments (19, 20).
How ocean Mn nodules grow is a subject of intensive research and some debate. Nodules apparently grow principally by direct precipitation of Mn from seawater, but the types of reactions that occur in the water and at the precipitation surface are poorly known (2, 17). It also has been suggested that some Mn and Fe is supplied by upward diffusion through underlying reducing sediments (2). One scenario suggests that Mn oxide phases in ocean nodule form by catalytic oxidation and adsorption of Mn(II) on suitable substrates, such as mineral and rock fragments and fine-grained MnO2 and Fe(OH)3. Once initiated nodule formation is self-perpetuating because Fe and Mn are autocatalytically precipitated on the surface (2).
Indeed Mn oxides, and Mn nodules themselves, have been recommended as oxidation catalysts for automobile exhaust systems (21) and for the reduction of nitric acid pollutants (22). It also has been proposed that in some environments bacteria might be the dominant catalysts for Mn oxide precipitation (7). For example, Mn-oxidizing and Mn-reducing bacteria isolated from deep-sea nodules have been shown to increase experimental deposition of Mn onto pulverized nodules (23). More recent studies (summarized in ref. 24) indicate that microorganisms can accelerate the rate of Mn(II) oxidation by up to five orders of magnitude over abiotic oxidation, and thus are likely responsible for much natural Mn(II) oxidation.
Ocean nodules are of potential commercial interest because in addition to Mn they also contain significant amounts (several tenths to more than one weight percent) of Cu, Ni, Co, and other strategic metals (e.g., ref. 25). Laboratory experiments have shown that the sorption capacity of freshly precipitated Mn oxides is extremely high for a variety of metal cations (26–28). Thus in seawater, adsorption by Mn oxide deposits may be the most important mechanism for controlling the concentration of heavy metals (27). The relatively slow accretion rates for deep-sea nodules provide ample opportunity for adsorption of heavy metals and is consistent with observations that more rapidly growing nodules tend to have lower trace metal concentrations (17). It is unclear how the heavy metals are bound in the nodule Mn oxide minerals, or even in which phases they are concentrated. Experiments have demonstrated that adsorption of heavy metals by hydrous Mn oxides is accompanied by release of protons (H+), suggesting that the cations are bound into the Mn oxides’ atomic structures (27). Additional insights into the nature of the heavy metals likely await a more detailed understanding of the atomic structures and crystal chemistries of Mn oxide minerals in ocean nodules.
1. Mn Oxide Minerals and the Environment
The unusually high adsorption capacities and scavenging capabilities of Mn oxide/hydroxide minerals provides one of the primary controls of heavy metals and other trace elements in soils and aquatic sediments (28, 29). Understanding such controls is important for maintaining and improving fertility of soil, mitigating health affects in humans and animals, and for treatment of water for consumption and industrial use.
Because Mn oxide minerals commonly occur as coatings and fine-grained aggregates with large surface areas, they exert chemical influences far out of proportion to their concentrations (28). The presence of only tiny amounts (e.g., a fraction of a weight percent of soil or sediment) of Mn oxide minerals might be adequate to control distribution of heavy metals between earth materials and associated aqueous systems (28). Additionally, Mn oxides can act as important adsorbents of phosphate in natural waters and surface sediments (30).
Two useful applications of the scavenging ability of Mn oxide minerals are as geochemical exploration tools (25, 31, 32) and purification agents for drinking water (33). Recent studies also indicate that Mn oxide minerals in soils and stream sediments and as coatings on stream pebbles and boulders might serve as natural traps for heavy metals in contaminated waters from mines and other industrial operations (32, 34, 35). Similarly, Mn oxide absorbers effectively recover Ra, Pb, and Po from seawater (36), and it has been shown that the geochemical distribution of several naturally occurring radionuclides (234Th, 228Th, 228Ra, and 226Ra) is controlled by Fe and Mn oxides (37, 38).
Hydrous oxides of Mn occur in most soils as discrete particles and as coatings on other mineral grains. Mn is highly mobile in acid, organic soils of the temperate and subarctic zones, but in the more alkaline tropical soils Mn might concentrate with residual laterites (2). It has been noted that frequently observed influences of pH, organic matter, lime, and phosphate on heavy metal availability in soils are understood principally in terms of their influence on the chemistries of hydrous oxides of Mn and Fe (28).
The major Mn minerals reported in soils are lithiophorite, hollandite, and birnessite (39, 40); it is more typically the case, however, that because the Mn oxides are fine-grained and poorly crystalline (commonly referred to as amorphous) that no attempt is made to assign mineral designations.
Mn oxides in soils and sediments readily participate in a wide variety of oxidation-reduction and cation-exchange reactions.
They exhibit large surface areas and can be very chemically active. Birnessite directly oxidizes Se(IV) to Se(VI) via a surface mechanism (41), Cr(III) to Cr(VI) (42), and As(III) to As(V) (43). Certain Mn oxide minerals easily oxidize arsenate (III), the more toxic form of inorganic As, to arsenate(V), which can more effectively be removed from drinking water by existing water treatment procedures (44). Mn oxide minerals such as birnessite and todorokite readily undergo cation-exchange reactions (45), and studies have shown that the cation exchange capacity of Mn dioxide at pH 8.3 (about that of seawater) exceeds that of montmorillanite (46). Clearly, these kinds of reactions profoundly affect the chemistries of soils and associated aqueous solutions.
2. Mn Oxide Minerals
What accounts for the complexity and impressive variety of Mn oxide minerals? Mn occurs in natural systems in three different oxidation states: +2, +3, and +4, giving rise to a range of multivalent phases. Mn oxides also display a remarkable diversity of atomic architectures, many of which easily accommodate a wide assortment of other metal cations. Finally, Mn is abundant in most geological systems and forms minerals under a wide range of chemical and temperature conditions, and through biological interactions.
Most Mn oxide minerals are brown-black and typically occur as intimately intermixed, fine-grained, poorly crystalline masses or coatings. Not surprisingly, identifying the particular mineral(s) in a Mn oxide specimen can pose quite a challenge. Hence many scientists report simply “Mn oxide,” rather than a particular mineral phase. Geologists have attempted to avoid the problem by simply referring to all soft (i.e., it blackens your fingers), brown-black, fine-grained specimens that were assumed to be Mn oxides as “wad.” Similarly, hard (does not blacken your fingers), gray-black, botroyoidal, massive specimens were called “psilomelane.” Recent studies have shown that most so-called psilomelane specimens are predominantly the mineral romanechite (Ba.66Mn5O10⋅1.34H2O). There is no comparable correlation between specimens labeled wad and any particular Mn oxide mineral.
Even today identification of the minerals in many Mn oxide samples is not straightforward. In general, powder x-ray diffraction is diagnostic for well-crystallized, monophasic samples. Unfortunately, the crystal structures, and consequently, the powder diffraction patterns are similar for many of the Mn oxide minerals. In many cases, it is necessary to supplement powder x-ray diffraction studies with other techniques, such as transmission electron microscopy (TEM), IR spectroscopy, and electron microprobe analysis.
Despite the fact that Mn oxides have been extensively studied for the past several decades, the details of many of their atomic structures are poorly understood, and there are several phases for which even the basic crystal structures are not known. This paucity of crystallographic data has greatly hindered research on the fundamental geochemical behaviors of common Mn oxide minerals. In most cases the major limiting factor is the lack of crystals suitable for single-crystal x-ray or neutron diffraction experiments.
In the past few years, however, other techniques such as TEM (high-resolution imaging and electron diffraction) and Rietveld refinements using powder x-ray and neutron diffraction data have provided important new insights into the atomic structures of Mn oxide minerals. The Rietveld method (see review in ref. 47) has made it possible to partially solve and refine structures from data collected from even relatively poorly crystalline samples (e.g., refs. 48 and 49).
Question
1. What is the importance of manganese dioxide?
What are the uses of manganese dioxide? MnO2 is primarily used as a part of dry cell batteries: alkaline batteries and the so-called Leclanché cell, or zinc–carbon batteries. For this application, approximately 500,000 tons are consumed annually.
2. What is the basic information of manganese?
It is gray-white, resembling iron, but is harder and very brittle. The metal is reactive chemically and decomposes slowly in cold water. Manganese is used to form many important alloys. Manganese improves rolling and forging qualities in steel, along with adding strength, stiffness, wear resistance, hardness.
3. What are the functions of manganese dioxide?
(in 2016) determined that the manganese dioxide lowers the combustion temperatures for wood from above 350°C (662°F) to 250°C (482°F), making fire making much easier and this is likely to be the purpose of the blocks.
4. What is manganese oxide used for?
Manganese oxide minerals have been used for thousands of years—by the ancients for pigments and to clarify glass, and today as ores of Mn metal, catalysts, and battery material. More than 30 Mn oxide minerals occur in a wide variety of geological settings.
5. What are the effects of manganese dioxide?
Inhalation exposure to high concentrations of manganese dusts (specifically manganese dioxide [MnO2] and manganese tetroxide [Mn3O4]) can cause an inflammatory response in the lung, which, over time, can result in impaired lung function.