Manganese is a gray-white metal resembling iron. It is a hard metal and is
very brittle, fusible with difficulty, but easily oxidized. Manganese metal and
its common ions are paramagnetic. This means that, while manganese metal does
not form a permanent magnet, it does exhibit strong magnetic properties in the
presence of an external magnetic field.
The most common oxidation states of manganese are +2, +3, +4, +6 and +7,
though oxidation states from +1 to +7 are observed. Mn2+ often
competes with Mg2+ in biological systems, and manganese compounds
where manganese is in oxidation state +7 are powerful oxidizing agents.
Compounds
Methylcyclopentadienyl manganese tricarbonyl is used as an additive in
unleaded gasoline to boost octane rating and reduce engine knocking.
Manganese dioxide is also used as a reagent in organic chemistry for the
oxidation of benzylic alcohols (i.e. adjacent to an aromatic ring).
Manganese(IV) oxide (manganese dioxide, MnO2) is used in dry cells.
Manganese can be used to neutralize the greenish tinge in glass caused by trace
amounts of iron contamination. Manganese compounds in larger amounts can color
glass an amethyst color, and are responsible for the purple color of true
amethyst. MnO2 is also used in the manufacture of oxygen and
chlorine, and in drying black paints. Manganese oxide is a brown pigment that
can be used to make paint and is a constituent of natural umber. Potassium
permanganate, sodium permanganate and barium permanganate are all potent
oxidizers. Potassium permanganate, also called Condy's crystals, is a commonly
used laboratory reagent because of its oxidizing properties and finds use as a
topical medicine (for example, in the treatment of fish diseases). Solutions of
potassium permanganate were among the first stains and fixatives to be used in
the preparation of biological cells and tissues for electron microscopy.
Manganese phosphating is used as a treatment for rust and corrosion
prevention on steel.
Manganese(IV) oxide (manganese dioxide) was used in the original type of dry
cell battery, and is the black material found when opening carbon-zinc type
flashlight cells. The same material also functions in newer alkaline batteries
(usually battery cells), which use the same basic reaction but a different
electrolyte.
The overall level and nature of manganese use in the United States is
expected to remain about the same in the near term. No practical technologies
exist for replacing manganese with other materials or for using domestic
deposits or other accumulations to reduce the complete dependence of the United
States on other countries for manganese ore.
Substitutes: Manganese has no satisfactory substitute in its major
applications, which are related to metallurgical alloy use. 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.
The most stable oxidation state for manganese is +2, and many manganese(II)
compounds are known, such as manganese(II) sulfate (MnSO4) and
manganese(II) chloride (MnCl2). This oxidation state is also seen in
the mineral rhodochrosite, (manganese(II) carbonate). The +3 oxidation state is
also known, in compounds such as manganese(III) acetate, but these are quite
powerful oxidizing agents.
Metal Alloys
Manganese is essential to iron and steel production by virtue of its
sulfur-fixing, deoxidizing, and alloying properties. Steelmaking, including its
ironmaking component, has accounted for most manganese demand, presently in the
range of 85% to 90% of the total demand. Among a variety of other uses,
manganese is a key component of low-cost stainless steel formulations and
certain widely used aluminium alloys.
The metal is very occasionally used in coins; the only United States coins to
use manganese were the "Wartime" nickel from 1942–1945, and, since 2000, dollar
coins. The EU uses manganese in 1 and 2 Euro coins due to greater and cheaper
availability.
Hisory
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 loadstone 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. This mineral is never magnetic (although manganese itself is
paramagnetic). In the 16th century, it was called manganesum by glassmakers,
possibly as a corruption 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). 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.
Manganese compounds were in use in prehistoric times; paints that were
pigmented with manganese dioxide can be traced back 17,000 years. The Egyptians
and Romans used manganese compounds in glass-making, to either remove color from
glass or add color to it. Manganese can be found in the iron ores used by the
Spartans. Some speculate that the exceptional hardness of Spartan steels derives
from the inadvertent production of an iron-manganese alloy. In the 17th century,
German chemist Johann Glauber first produced permanganate, a useful laboratory
reagent (although some people believe that it was discovered by Ignites Kaim in
1770). By the mid-18th century, manganese dioxide was in use in the manufacture
of chlorine (which it produces when mixed with hydrochloric acid, or
commercially with a mixture of dilute sulfuric acid and sodium chloride). The
Swedish chemist Scheele was the first to recognize that manganese was an
element, and his colleague, Johan Gottlieb Gahn, isolated the pure element in
1774 by reduction of the dioxide with carbon. Around the beginning of the 19th
century, scientists began exploring the use of manganese in steelmaking, with
patents being granted for its use at the time. In 1816, it was noted that adding
manganese to iron made it harder, without making it any more brittle. In 1837,
British academic James Couper noted an association between heavy exposure to
manganese in mines with a form of Parkinson's Disease. In 1912, manganese
phosphating electrochemical conversion coatings for protecting firearms against
rust and corrosion were patented in the United States, and have seen widespread
use ever since.
In the 20th century, manganese dioxide has seen wide commercial use as the
chief cathodic material for commercial disposable dry cells and dry batteries of
both the standard (carbon-zinc) and alkaline type.
Isotopes
Naturally occurring manganese is composed of 1 stable isotope;
55Mn. 18 radioisotopes have been characterized with the most stable
being 53Mn with a half-life of 3.7 million years, 54Mn
with a half-life of 312.3 days, and 52Mn with a half-life of 5.591
days. All of the remaining radioactive isotopes have half lives that are less
than 3 hours and the majority of these have half lives that are less than 1
minute. This element also has 3 meta states.
Manganese is part of the iron group of elements which are thought to be
synthesized in large stars shortly before supernova explosion. 53Mn
decays to 53Cr with a half-life of 3.7 million years. Because of its
relatively short half-life, 53Mn is an extinct radionuclide.
Manganese isotopic contents are typically combined with chromium isotopic
contents and have found application in isotope geology and radiometric dating.
Mn-Cr isotopic ratios reinforce the evidence from 26Al and
107Pd for the early history of the solar system. Variations in
53Cr/52Cr and Mn/Cr ratios from several meteorites
indicate an initial 53Mn/55Mn ratio that suggests Mn-Cr
isotopic systematics must result from in-situ decay of 53Mn in
differentiated planetary bodies. Hence 53Mn provides additional
evidence for nucleosynthetic processes immediately before coalescence of the
solar system.
The isotopes of manganese range in atomic weight from 46 u (46Mn)
to 65 u (65Mn). The primary decay mode before the most abundant
stable isotope, 55Mn, is electron capture and the primary mode after
is beta decay.
Occurence
Manganese occurs principally as pyrolusite (MnO2), and to a lesser
extent as rhodochrosite (MnCO3). Land-based resources are large but
irregularly distributed; those of the United States are very low grade and have
potentially high extraction costs. Over 80% of the known world manganese
resources are found in South Africa and Ukraine. Other important manganese
deposits are in China, Australia, Brazil, Gabon, India, and Mexico.
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%.
Manganese is mined in Burkina Faso and Gabon.
Vast quantities of manganese exist in manganese nodules on the ocean floor.
Attempts to find economically viable methods of harvesting manganese nodules
were abandoned in the 1970s.
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