Manganese (pronounced /ˈmæŋɡəniːz/, MANG-gən-neez) is a chemical element, designated by the symbol Mn.
It has the atomic number 25. It is found as a free
element in nature (often in combination with iron), and in many minerals.
As a free element, manganese is a metal with important industrial metal alloy
uses, particularly in stainless steels.
Detailed description:
Manganese phosphating is used as a
treatment for rust and corrosion prevention on steel. Depending on their
oxidation state, manganese ions have various colors and are used industrially
as pigments.
The permanganates
of alkali
and alkaline earth metals are powerful oxidizers.
Manganese dioxide is used as the cathode (electron acceptor) material in
standard and alkaline disposable dry cells and batteries.
Manganese(II)
ions function as cofactors for a number of enzymes in higher
organisms, where they are essential in detoxification of superoxide
free radicals. The element is a required trace mineral for all known living
organisms. In larger amounts, and apparently with far greater activity by
inhalation, manganese can cause a poisoning
syndrome in mammals, with neurological damage which is sometimes
irreversible.
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Characteristics
Physical properties
Manganese
is a silvery-gray metal
resembling iron. It is hard and very brittle, difficult to fuse, but easy to
oxidize.[1]
Manganese metal and its common ions are paramagnetic.[2]
The
origin of the name manganese is complex. In ancient times, two black minerals
from Magnesia
in what is now modern Greece were both called magnes, but were thought
to differ in gender. The male magnes attracted iron, and was the iron
ore we now know as lodestone or magnetite,
and which probably gave us the term magnet. The female magnes
ore did not attract iron, but was used to decolorize glass. This feminine magnes
was later called magnesia, known now in modern times as pyrolusite
or manganese dioxide. Neither this mineral nor
manganese itself is magnetic. In the 16th century, manganese dioxide was called
manganesum (note the two n's instead of one) by glassmakers, possibly as a
corruption and concatenation of two words, since alchemists and glassmakers
eventually had to differentiate a magnesia
negra (the black ore) from magnesia alba (a white ore,
also from Magnesia, also useful in glassmaking). Michele
Mercati called magnesia negra Manganesa, and finally the metal
isolated from it became known as manganese (German: Mangan). The name magnesia
eventually was then used to refer only to the white magnesia alba (magnesium
oxide), which provided the name magnesium for that free element, when it was eventually
isolated, much later.[9]
Occurrence and production
Manganese
makes up about 1000 ppm (0.1%) of the Earth's
crust, making it the 12th most abundant element there.[19]
Soil contains 7–9000 ppm of manganese with an average of 440 ppm.[19]
Seawater has only 10 ppm manganese and the atmosphere
contains 0.01 µg/m3.[19]
Manganese occurs principally as pyrolusite
(MnO2), braunite, (Mn2+Mn3+6)(SiO12),[20]
psilomelane
(Ba,H2O)2Mn5O10, and to a lesser
extent as rhodochrosite (MnCO3).
The
most important manganese ore is pyrolusite (MnO2). Other economically important
manganese ores usually show a close spatial relation to the iron ores.[1]
Land-based resources are large but irregularly distributed. Over 80% of the
known world manganese resources are found in South
Africa and Ukraine,
other important manganese deposits are in Australia, India, China, Gabon and Brazil.[21]
In 1978 it was estimated that 500 billion tons of manganese
nodules exist on the ocean floor.[22]
Attempts to find economically viable methods of harvesting manganese nodules
were abandoned in the 1970s.[23]
Manganese
is mined in South Africa, Australia, China, Brazil, Gabon, Ukraine, India and
Ghana and Kazakhstan.
US Import Sources (1998–2001): Manganese ore: Gabon, 70%; South Africa, 10%;
Australia, 9%; Mexico, 5%; and other, 6%. Ferromanganese: South Africa, 47%;
France, 22%; Mexico, 8%; Australia, 8%; and other, 15%. Manganese contained in
all manganese imports: South Africa, 31%; Gabon, 21%; Australia, 13%; Mexico,
8%; and other, 27%.[21][24]
For
the production of ferromanganese, the manganese ore are mixed with iron
ore and carbon and then reduced either in a blast furnace or in an electric arc
furnace.[25]
The resulting ferromanganese has a manganese content of 30 to 80%.[1]
Pure manganese used for the production of non-iron alloys is produced by leaching manganese ore with sulfuric
acid and a subsequent electrowinning process.[26]
Applications
Manganese
has no satisfactory substitute in its major applications, which are related to
metallurgical alloy use.[21]
In minor applications, (e.g., manganese phosphating), zinc and sometimes vanadium are
viable substitutes. In disposable battery manufacture, standard and alkaline
cells using manganese will probably eventually be mostly replaced with lithium
battery technology.
Steel
Manganese
is essential to iron and steel production by virtue of its sulfur-fixing, deoxidizing,
and alloying
properties. Steelmaking,[27]
including its ironmaking component, has accounted for most manganese demand,
presently in the range of 85% to 90% of the total demand.[26]
Among a variety of other uses, manganese is a key component of low-cost stainless
steel formulations.[24][28]
editAluminium alloys
Main article: Aluminium alloy
The
second large application for manganese is as alloying agent for aluminium.
Aluminium with a manganese content of roughly 1.5% has an increased resistance
against corrosion due to the formation of grains absorbing impurities which
would lead to galvanic corrosion.[32]
The corrosion resistant aluminium alloy 3004 and 3104 with a
manganese content of 0.8 to 1.5% are the alloy used for most of the beverage
cans.[33]
Before year 2000, in excess of 1.6 million metric tons have been used of those
alloys, with a content of 1% of manganese this amount would need 16,000 metric
tons of manganese.[33]
Other uses
Manganese(IV) oxide (manganese dioxide, MnO2)
is used as a reagent in organic chemistry for the oxidation of
benzylic alcohols
(i.e. adjacent to an aromatic ring). Manganese dioxide has been used since antiquity
to oxidatively neutralize the greenish tinge in glass caused by trace amounts
of iron contamination.[13]
MnO2 is also used in the manufacture of oxygen and chlorine, and in
drying black paints. Manganese(IV) oxide was used in the original
type of dry cell battery as an electron acceptor from zinc,
and is the blackish material found when opening carbon–zinc type flashlight
cells. The manganese dioxide is reduced to the manganese oxide-hydroxide
MnO(OH) during discharging, preventing the formation of hydrogen at the anode
of the battery.[35]
MnO2 + H2O +
e− → MnO(OH) + OH−
The
same material also functions in newer alkaline batteries (usually battery
cells), which use the same basic reaction, but a different electrolyte mixture.
In 2002 more than 230,000 tons of manganese dioxide was used for this
purpose.[18][35]
The
metal is very occasionally used in coins; until 2000 the only United States
coin to use manganese was the "wartime" nickel from
1942–1945.[36]
An alloy of 75% copper and 25% nickel was traditionally used for the production
of nickel coins. However, because of shortage of nickel metal during the war,
it was substituted by more available silver and manganese, thus resulting in an
alloy of 56% copper, 35% silver and 9% manganese.
Biological role
Manganese
is an essential trace nutrient in all forms of life.[19]
The classes of enzymes that have manganese cofactors are very broad and include oxidoreductases,
transferases,
hydrolases,
lyases, isomerases,
ligases, lectins, and integrins.
The reverse transcriptases of many retroviruses
(though not lentiviruses
such as HIV) contain
manganese. The best known manganese-containing polypeptides
may be arginase,
the diphtheria toxin, and Mn-containing superoxide dismutase (Mn-SOD).[39]
Mn-SOD
is the type of SOD present in eukaryotic mitochondria, and also in most
bacteria (this fact is in keeping with the bacterial-origin theory of
mitochondria). The Mn-SOD enzyme is probably one of the most ancient, for
nearly all organisms living in the presence of oxygen use it to deal with the
toxic effects of superoxide, formed from the 1-electron reduction of
dioxygen. Exceptions include a few kinds of bacteria such as Lactobacillus plantarum and related lactobacilli,
which use a different non-enzymatic mechanism, involving manganese (Mn2+)
ions complexed with polyphosphate directly for this task, indicating how this
function possibly evolved in aerobic life.
The
human body contains about 10 mg of manganese, which is stored mainly in
the liver and kidneys. In the human brain the manganese is bound to manganese metalloproteins
most notably glutamine synthetase in astrocytes.
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