Iron ores are rocks & minerals
from which metallic iron can be extracted
types of iron ore
a) oxide ores
Ex : hematite (fe2o3)
fe (t) - 69.9%
magnetite
fe(t)- 74.2%
b) hydroxide ore
Ex :limonite(2fe2o3+3H2O)
c) sulphide ore
Ex : pyrite(fes2)
d) carbonates ores
Ex : siderite (feco3)
Chemical analysis
fe(total) = 67.5-68%
Loi = 0.3 -0.5%
sio2 +al203 = >2%
p = 0.02-0.03%
moisture = 0.2-0.4 %
physical analysis
Tumbular index = 93-94%
screen analysis
+18mm = nill
+15mm = 10-12%
+10 mm = 40-45%
+ 8mm = 10-12%
+ 5mm = 18-20%
- 5mm = 2%
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| MGM VIRGIN IRON ORE |
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| ROM |
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MGM IRON ORE CRUSHING &SCREENING UNIT |
Iron
ore
From Wikipedia, the free
encyclopedia
Iron ores
are rocks and minerals from which metallic iron
can be
economically extracted. The ores are usually rich in
iron
oxides and vary in colour from dark grey, bright
yellow,
deep purple, to rusty red. The iron itself is usually
found in
the form of magnetite (Fe3O4),
hematite (Fe2O3),
goethite,
limonite or siderite. Hematite is also known as
"natural
ore". The name refers to the early years of mining,
when
certain hematite ores contained 66% iron and could be
fed
directly into iron making blast furnaces. Iron ore is the
raw
material used to make pig iron, which is one of the
main raw
materials to make steel. 98% of the mined iron
ore is
used to make steel.[1]
Sources
Pure iron
is virtually unknown on the surface of the Earth except as Fe-Ni alloys from
meteorites and very rare forms of deep mantle xenoliths. Therefore, all sources
of iron used by human industry exploit iron oxide minerals, the primary form
which is used in industry being hematite. However, in some situations, more
inferior iron ore sources have been used by industrialized societies when
access to high-grade hematite ore was not available. This has included
utilisation of taconite in the United States, particularly during World War II,
and goethite or bog ore used during the American Revolution and the Napoleonic
wars. Magnetite is often used because it is magnetic and hence easily
liberated
from the gangue minerals. Inferior sources of iron ore generally require
beneficiation. Due to the high density of hematite relative
Contents
_ 1
Sources
_ 1.1
Magnetite banded iron deposits
_ 1.2
Magmatic magnetite ore deposits
_ 1.3
Hematite ore
_ 2
Production and consumption
_ 3
Depletion
_ 4
Smelting
_ 4.1
Trace Elements:Effects and Remedies
_ 4.1.1
Silicon
_ 4.1.2
Phosphorus
_ 4.1.3
Aluminium
_ 4.1.4
Sulfur
_ 5
References
_ 6
External links
Hematite:
the main iron ore in Brazilian
Mines This
heap of iron ore pellets will be used in
steel
production. Make a donation to Wikipedia and give the gift of knowledge!
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7/6/200 to silicates, beneficiation usually
involves a combination of crushing and milling as well as heavy liquid
separation. This is achieved by passing the finely crushed ore over a bath of
solution containing bentonite or other agent which increases the density of the
solution. When the density of the solution is
properly
calibrated, the hematite will sink and the silicate mineral fragments will
float and can bremoved.
Iron ore
mining methods vary by the type of ore being mined. There are four main types
of iron ore
deposits
worked currently, depending on the mineralogy and geology of the ore deposits.
These are magnetite, titanomagnetite, massive hematite and pisolitic ironstone
deposits.
Magnetite
banded iron deposits
Banded
iron formations (BIF) are fine grained metamorphosed sedimentary rocks composed
predominantly of magnetite and silica (as quartz). Banded Iron formations are
locally known as taconit within North America. Mining of BIF formations
involves coarse crushing and screening, followed by rough crushing and fine
grinding to comminute the ore to the point where the crystallised magnetite and
quartz are fine enough that the quartz is left behind when the resultant powder
is passed under a magnetic separator. The mining involves moving tremendous
amounts of ore and waste. The waste comes in two forms, bedrock in the mine
(mullock) that isn't ore, and unwanted minerals which are an intrinsic part of
the ore rock itself (gangue). The mullock is mined and piled in waste dumps,
and the gangue is separated during
the
beneficiation process and is removed as tailings. Taconite tailings are mostly
the mineral quartz, which is chemically inert. This material is stored in
large, regulated water settling ponds. The key economic parameters for
magnetite ore being economic are the crystallinity of the magnetite, the grade
of the iron within the BIF host rock, and the contaminant elements which exist
within the magnetite concentrate. The size and strip ratio of most magnetite
resources is irrelevant as BIF formations can be hundreds of metres thick, with
hundreds of kilometres of strike, and can easily come to more than 2,500
million tonnes of contained ore. The typical grade of iron at which a
magnetite-bearing banded iron formation becomes economic is roughly 25% Fe,
which can generally yield a 33% to 40% recovery of magnetite by weight, to
produce a
concentrate
grading in excess of 64% Fe by weight. The typical magnetite iron ore
concentrate has less than 0.1% phosphorus, 3-7% silica and less than 3%
aluminium.
The grain
size of the magnetite and its degree of comingling with the silica groundmass
determine the grind size to which the rock must be comminuted to enable
efficient magnetic separation to provide ahigh purity magnetite concentrate.
This determines the energy inputs required to run a milling operation.
Generally
most magnetite BIF deposits must be ground to between 32 and 45 micrometres in
order to provide a low-silica magnetite concentrate. Magnetite concentrate
grades are generally in excess of 63% Fe by weight and usually are low
phosphorus, low aluminium, low titanium and low silica and demand a
premium
price. Currently magnetite iron ore is mined in Minnesota and Michigan in the
U.S., and Eastern Canada mine taconite. Magnetite bearing BIF is currently
mined extensively in Brazil, which exports significant quantities to Asia, and
there is a nascent and large magnetite iron ore industry in Australia.
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Magmatic
magnetite ore deposits
Occasionally
granite and ultrapotassic igneous rocks segregate magnetite crystals and form
masses of magnetite suitable for economic concentration. A few iron ore
deposits, notably in Chile, are formed from volcanic flows containing
significant accumulations of magnetite phenocrysts. Chilean magnetite iron ore
deposits within the Atacama Desert have also formed alluvial accumulations of
magnetite in streams leading from these volcanic formations. Some magnetite
skarn and hydrothermal deposits have been worked in the past as high-grade iron
ore deposits requiring little beneficiation. There are several
granite-associated deposits of this nature in Malaysia and Indonesia.
Other
sources of magnetite iron ore include metamorphic accumulations of massive
magnetite ore such as at Savage River, Tasmania, formed by shearing of
ophiolite ultramafics. Another, minor, source of iron ores are magmatic
accumulations in ultramafic to mafic layered intrusions which contain a
typically titanium-bearing magnetite crystal rock (magnetitite) often with vanadium.
These ores form a niche market, with specialty smelters used to recover the
iron, titanium and vanadium. These ores are beneficiated essentially similar to
banded iron formation ores, but usually are
more
easily upgraded via crushing and screening. The typical titanomagnetite
concentrate grades 57%
Fe, 12% Ti
and 0.5% V2O5.
Hematite
ore
Hematite
iron ore deposits are currently exploited on all continents, with the largest
intensity in South America, Australia and Asia. Most large hematite iron ore
deposits are sourced from metasomatically altered banded iron formations and
rarely igneous accumulations. Hematite iron is typically rarer than magnetite
bearing BIF or other rocks which form its main source or protolith rock, but it
is considerably cheaper and easier to beneficiate the hematite ores and
requires considerably less energy to crush and grind. Hematite ores however can
contain significantly higher concentrations of penalty elements, typically
being higher in phosphorus, water content (especially
pisolite
sedimentary accumulations) and aluminium (clays within pisolites).
In
Australia iron ore is won from three main sources: pisolite "channel iron
deposit" ore derived by mechanical erosion of primary banded-iron
formations and accumulated in alluvial channels such as at Pannawonica, Western
Australia; and the dominant metasomatically-altered banded iron formation
related
ores such as at Newman, the Chichester Range, the Hamersley Range and
Koolyanobbing, Western Australia. Other types of ore are coming to the fore
recently, such as oxidised ferruginous hardcaps, for instance laterite iron ore
deposits near Lake Argyle in Western Australia. The total recoverable reserves
of iron ore in India are about 9,602 million tones of hematite and 3,408 million
tones of magnetite. Madhya Pradesh, Karnataka, Bihar, Orissa, Goa, Maharashtra,
Andhra Pradesh, Kerala, Rajasthan and Tamil Nadu are the principal Indian
producers of iron ore.
Production
and consumption
Iron ore -
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Iron is
the world's most commonly used metal. It is used primarily
in
structural engineering applications and in maritime purposes,
automobiles,
and general industrial applications (machinery).
Iron-rich
rocks are common worldwide, but ore-grade commercial
mining
operations are dominated by the countries listed in the table
aside. The
major constraint to economics for iron ore deposits is
not
necessarily the grade or size of the deposits, because it is not
particularly
hard to geologically prove enough tonnage of the rocks
exist. The
main constraint is the position of the iron ore relative to
market,
the cost of rail infrastructure to get it to market and the
energy
cost required to do so.
World
production averages one billion metric tons of raw ore
annually.
The world's largest producer of iron ore is the Brazilian
mining
corporation Vale, followed by Anglo-Australian companies
BHP
Billiton and Rio Tinto Group. A further Australian supplier,
Fortescue
Metals Group Ltd may eventually bring Australia's
production
to second in the world.
World
consumption of iron ore grows 10% per annum on average
with the
main consumers being China, Japan, Korea, the United
States and
the European Union.
China is
currently the largest consumer of iron ore, which translates
to be the
world's largest steel producing country. China is followed
by Japan
and Korea, which consume a significant amount of raw
iron ore
and metallurgical coal. In 2006, China produced 588
million
tons of iron ore, with an annual growth of 38%.
]
Smelting
Iron ore
consists of oxygen and iron atoms bonded together into molecules. To convert it
to metallic iron it must be smelted or sent through a direct reduction process
to remove the oxygen. Oxygen-iron bonds are strong, and to remove the iron from
the oxygen, a stronger elemental bond must be presented to attach to the
oxygen. Carbon is used because the strength of a carbon-oxygen bond is greater
than that of the iron-oxygen bond, at high temperatures. Thus, the iron ore
must be powdered and mixed with coke, to be burnt in the smelting process.
However,
it is not entirely as simple as that; carbon monoxide is the primary ingredient
of chemicall Estimated iron ore
production in million metric tons for 2006
according
to U.S. Geological Survey
[2]
Country
Production
China 520
Brazil 300
Australia 270
India 150
Russia 105
Ukraine 73
United
States 54
South
Africa 40
Canada 33
Sweden 24
Venezuela 20
Iran 20
Kazakhstan
15
Mauritania
11
Other
countries 43
Total
world 1690
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stripping
oxygen from iron. Thus, the iron and carbon smelting must be kept at an oxygen
deficient reduced state to promote burning of carbon to produce CO not CO2.
Air blast
and charcoal (coke): 2C + O2 2CO.
Carbon
monoxide (CO) is the principal reduction agent.
Stage One:
3Fe2 O3 +
CO 2Fe3 O4
+ CO2
Stage Two:
Fe3 O4 +
CO 3Fe O + CO2
Stage
Three: FeO + CO Fe + CO2
Limestone
fluxing chemistry: CaCO3 CaO + CO2
Trace Elements:Effects and
Remedies
The
inclusion of even small amounts of some elements can have profound effects on
the behavioral characteristics of a batch of iron or the operation of a
smelter. These effects can be both good and bad. Some catastrophically bad.
Some chemicals were deliberately added. The addition of a flux made a blast furnace
more efficient. Others were added because they made the iron more fluid,
harder, or some other desirable quality. The choice of ore, fuel, and flux determined
how the slag behaved and the operational characteristics of the iron produced.
Ideally iron ore contains only iron and oxygen. In nature this is rarely the
case. Typically, iron ore contains a host of elements which are often unwanted
in modern steel.
Silicon
Silica
(SiO2) is almost always present in iron ore. Most of it is slagged off during
the smelting process. But, at temperatures above 1300 °C some will be reduced
and form an alloy with the iron. The hotter the furnace, the more silicon will
be present in the iron. It is not uncommon to find up to 1.5% Si in European
cast iron from the 16th to 18th centuries. The major effect of silicon is to
promote the formation of gray iron. Gray iron is less brittle and easier to
finish than white iron. It was preferred for casting purposes for this reason.
Turner (1900:192-7) reported that silicon also reduced shrinkage and
the
formation of blowholes, lowering the number of bad castings
Phosphorus
Phosphorus
(P) has four major effects on iron: increased hardness and strength, lower
solidus temperature, increased fluidity, and cold shortness. Depending on the
use intended for the iron, these effects are either good or bad. Bog ore often
has a high Phosphorus content (Gordon 1996:57).
The
strength and hardness of iron increases with the concentration of phosphorus.
0.05% phosphorus in wrought iron makes it as hard as medium carbon steel. High
phosphorus iron can also be hardened by cold hammering. The hardening effect is
true for any concentration of phosphorus. The more phosphorus, the harder the
iron becomes and the more it can be hardened by hammering. Modern steel
makers can
increase hardness by as much as 30%, without sacrificing shock resistance by
maintaining phosphorus levels between 0.07 and 0.12%. It also increases the
depth of hardening due to quenching, but at the same time also decreases the
solubility of carbon in iron at high temperatures. This would decrease its
usefulness in making blister steel (cementation), where the speed and amount of
carbon absorption is the overriding consideration.
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The
addition of phosphorus has a down side. At concentrations higher than 0.2% iron
becomes increasingly cold short, or brittle at low temperatures. Cold short is
especially important for bar iron. Although, bar iron is usually worked hot,
its uses often require it to be tough, bendable, and resistant to shock at room
temperature. A nail that shattered when hit with a hammer or a carriage wheel
that broke when it hit a rock would not sell well. High enough concentrations
of phosphorus render any iron unusable (Rostoker and Bronson 1990:22). The
effects of cold shortness are magnified by temperature.
Thus, a piece
of iron that is perfectly serviceable in summer, might become extremely brittle
in winter. There is some evidence that during the Middle Ages the very wealthy
may have had a high phosphorus sword for summer and a low phosphorus sword for
winter (Rostoker and Bronson 1990:22). Careful control of phosphorus can be of
great benefit in casting operations. Phosphorus depresses the liquidus
temperature, allowing the iron to remain molten for longer and increases
fluidity. The addition of 1% can double the distance molten iron will flow
(Rostoker and Bronson 1990:22). The maximum effect, about 500 °C, is achieved
at a concentration of 10.2% (Rostocker and Bronson 1990:194). Forfoundry work
Turner felt the ideal iron had 0.2-0.55% phosphorus. The resulting iron filled
molds with fewer voids and also shrank less. In the 19th century some producers
of decorative cast iron used iron with up to 5% phosphorus. The extreme
fluidity allowed them to make very complex and delicate
castings.
But, they could not be weight bearing, as they had no strength (Turner
1900:202-4).
There are
two remedies for high phosphorus iron. The oldest, and easiest, was avoidance.
If the iron your ore produced was cold
short, you found a new source of ore. The second method involves oxidizing the
phosphorus during the fining process by adding iron oxide. The technique is
usually associated with puddling in the 19th century, and may not have been
understood earlier. For instance Isaac Zane, the owner of Marlboro Iron Works
did not appear to know about it in 1772. Given Zane's
reputation
for keeping abreast of the latest developments, the technique was probably
unknown to the ironmasters of Virginia and Pennsylvania.
Phosphorus
is a deleterious contaminant because it makes steel brittle, even at
concentrations of as little as 0.5%. Phosphorus cannot be easily removed by
fluxing or smelting, and so iron ores must generally below in phosphorus to
begin with. The iron pillar of India which does not rust is protected by a phosphoric
composition. Phosphoric acid is used at a rust converter because phosphoric
iron is less susceptible to oxidation
.
Aluminium
Small
amounts of aluminium (Al) are present in many ores (often as clay) and some
limestone. The former can be removed by washing the ore prior to smelting.
Until the introduction of brick lined furnaces the amounts are small enough
that they do not have an effect on either the iron or slag. However, when brick
is used for hearths and the interior of blast furnaces, the amount of aluminium
increases dramatically. This is due to the erosion of the furnace lining by the
liquid slag, Aluminium is very hard to reduce. As a result aluminium
contamination of the iron is not a problem. However, it does increase the
viscosity of the slag (Kato and Minowa 1969:37 and Rosenqvist 1983:311). This
will have a number of adverse effects on furnace operation. The thicker slag
will slow
the
descent of the charge, prolonging the process. High aluminium will also make it
more difficult to tap off the liquid slag. At the extreme this could lead to a
frozen furnace.
There are
a number of solutions to a high aluminium slag. the first is avoidance, don't
use ore or a lime
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source
with a high aluminium content. Increasing the ratio of lime flux will decrease
the viscosity
(Rosenqvist
1983:311).
Sulfur
Sulfur (S)
is a frequent contaminant in coal. It is also present in small quantities in
many ores, but would be removed by calcining. Sulfur dissolves readily in both
liquid and solid iron at the temperatures present in iron smelting. The effects
of even small amounts of sulfur are immediate and serious. They were one of the
first worked out by iron makers. Sulfur causes iron to be red or hot short
(Gordon 1996:7).
Hot short
iron is brittle when hot. This was a serious problem as most iron used during
the 17th and 18th century was bar or wrought iron. Wrought iron is
shaped by repeated blows with a hammer while hot. A piece of hot short iron
will crack if worked with a hammer. When a piece of hot iron or steel cracks
the exposed surface immediately oxidizes. This layer of oxide prevents the
mending of the crack by welding. Large cracks cause the iron or steel to break
up. Smaller cracks can cause the object to fail during use. The degree of hot
shortness is in direct proportion to the amount of sulfur present. Today iron
with over 0.03% sulfur is avoided.
Hot short
iron can be worked, but it has to be worked at low temperatures. Working at
lower temperatures requires more physical effort from the smith or forgeman.
the metal must be struck more often and harder to achieve the same result. A
mildly sulfur contaminated bar could be worked, but it required a great deal
more time and effort.
In cast
iron sulfur promotes the formation of white iron. As little as 0.5% can
counteract the effects of slow cooling and a high silicon content (Rostoker and
Bronson 1990:21). White cast iron is more brittle, but also harder. It was
generally avoided, because it was difficult to work. Except in China where high
sulfur cast iron, some as high as 0.57%, made with coal and coke, was used to
make bells and chimes
(Rostoker,
Bronson, and Dvorak 1984:760). According to Turner (1900:200), good foundry iron
should
have less
than 0.15% sulfur. In the rest of the world a high sulfur cast iron could be
used for making castings, but would make poor wrought iron.
There are
a number of remedies for sulfur contamination. The first, and the one most used
in historic and prehistoric operations, was avoidance. Coal was not used in
Europe (unlike China) as a fuel for smelting because it contained sulfur and
caused hot short iron. If an ore resulted in hot short metal, ironmasters
found
another ore. When mineral coal was first used in European blast furnaces in
1709 (or perhaps
earlier),
it was coked. Only with the introduction of hot blast from 1829 was raw coal used. Sulfur can be removed from
ores by roasting and washing. Roasting oxidizes sulfur to form sulfur dioxide
which either escapes into the atmosphere or can be washed out. In warm climates
it was possible to leave pyritic ore out in the rain. The combined action of
rain, bacteria, and heat oxidize the sulfides to sulfates, which are water
soluble (Turner 1900:77). However, historically (at least) iron sulfide (iron
pyrite,
FeS2), though a common iron mineral has not
been used an ore for the production of metal. Natural weathering was also used
in Sweden. The same process, at geological speed, results in the gossan
limonite ores.
The
importance attached to low sulfur iron is demonstrated by the consistently
higher prices paid for the iron of Sweden, Russia, and Spain from the 16th to
18th centuries. Today sulfur is no longer a problem. The modern remedy is the
addition of manganese. But, the operator must know how much sulfur is in
Iron ore -
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_ This
page was last modified on 25 June 2008, at 16:29.
_ All
text is available under the terms of the GNU Free
Documentation
License. (See Copyrights for details.)
Wikipedia®
is a registered trademark of the Wikimedia
Foundation,
Inc., a U.S. registered 501(c)(3) tax-deductible
nonprofit
charity.
the iron
because at least five times as much manganese must be added to neutralize it.
Some historic irons display manganese
levels, but most are well below the level needed to neutralize sulfur (Rostoker
and Bronson 1990:21).
References
1. ^ IRON ORE - Hematite,
Magnetite & Taconite (http://www.mii.org/Minerals/photoiron.html). Mineral
Information Institute.
Retrieved on 2006-04-07.
2. ^ U.S. Geological Survey
(http://minerals.usgs.gov/minerals/pubs/commodity/iron_ore/). Retrieved on
2008-
01-29.
3. ^ Brown, Lester Plan B
2.0, New York: W.W. Norton, 2006. p. 109
_ Gordon,
Robert B. (1996). American Iron 1607-1900. The Johns Hopkins University Press.
_ Rostoker,
William and Bennet Bronson (1990). Pre-Industrial Iron: Its Technology and
Ethnology.
Archeomaterials Monograph No. 1.
_ Turner,
Thomas (1900). The Metallurgy of Iron. 2nd Edition. Charles Griffin &
Company,
Limited.
_ Kato,
Makoto and Susumu Minowa (1969). 'Viscosity Measurement of Molten Slag-
Properties of
Slag at
Elevated Temperature (Part 1)'. Transactions of the Iron and Steel Institute of
Japan Vol.
9:31-38.
Nihon Tekko Kyokai, Tokyo.
_ Rosenqvist,
Terkel (1983). Principles of Extractive Metallurgy. McGraw-Hill Book Company.
_ Rostoker,
William, Bennet Bronson, and James Dvorak (1984). 'The Cast-Iron Bells of
China'.
Technology
and Culture 25(4):750-67. The Society for the History of Technology.
External
links
_ History
of the Iron Ore Trade on the Great Lakes
(http://web.ulib.csuohio.edu/SpecColl/glihc/articles/carrhist.html)
_ United
States Colonial Iron Ore Industry
(http://www.lastgreatplaces.org/berkshire/history/art6162.html)
_ "Pioneers
of the Cleveland iron trade" by J. S. Jeans 1875
(http://www.archive.org/details/pioneersofclevel00jeaniala)
_ Iron
Mines of NY/NJ (http://www.abandonedmines.net/)
Retrieved
from "http://en.wikipedia.org/wiki/Iron_ore"
Categories:
Economic geology | Iron | Mining | Resource extraction
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MGM STEELS
ODISHA
