Iron Ore Pellets

In order to succesfully be made into steel in a blast furnace, iron ore needs to be in a form that allows the free movement of oxygen around the particles.  One way to achieve this is to agglomorate the ore into pellets, which are round balls of concentrated ore.  I will attempt to describe the iron ore pelletizing process below.

In the palletisation plant, a suitable binder such as Bentonite is added to ground iron ore or iron ore concentrate which is mixed in a high intensity mixer.  In order to harden the pellets, they are heated to temperatures between 1290C to 1340C. This treatment can sometimes cause certain chemical reactions to occur that change pellet’s properties. These reactions can include the dehydration of hematite or the oxidation of magnetite; in many cases “fluxed pellets” are produced by the addition of limestone or dolomite to the balling feed. These additions react with the gangue in the iron ore to enhance the performance of the pellets in certain downstream processing steps.

Iron ore pellets can be made by two different processes, the Straight Grate process and the Grate Kiln process.  The Grate kiln system consists of three machines; a traveling grate, a rotary kiln and an annular cooler which heats, hardens and cools the ore respectively.  These three different machines can be independently controlled, all operating at different speeds etc.  This is not possible in a Straight Gate system as this consists of one continuous conveyor.  This flexibility of the Grate Kiln process means that it can be switched from processing Magnetite to processing Hematite in just a few hours.

The travelling gate is for drying and pre-heating of the balls before they are transferred to the rotary kiln. The balls do not have the physical properties necessary to survive direct feeding to the rotary kiln and must be semi-hardened and to do this, the balls have to be substantially heated and any fluxstone carbonates need to be calcinated by removing any Carbon Dioxide.

The rotary kiln is a downwards-sloping cylinder from the traveling grate to the annular cooler.  The rate of flow through the kiln is controlled by the speed of rotation and while they are traveling through the cylinder, there is a mixing action on the pellets. This action is important because it creates a uniform pellet size and all of the pellets are exposed to the burner flame for an equal amount of time.  At the discharge end of the rotary kiln is a single burner, which uses the hot air from the annular cooler for combustion. Various different fuels such as oil, gas or coal can be used to start the combustion process.

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The annular cooler is similar to the traveling grate.  The hot pellets from the rotary kiln are fed into the annular cooler and air is forced upwards through the conveyors and the bed to avoid exposure of the machine parts to high temperatures.  The pellets are levelled in the cooler to a depth of 660 mm and conveyed over several cooling zones. The various cooling zones are designed in such a way that they will recover the maximum heat from the hot pellets and various ducts carry this hot air to the other parts of the process.   The cooled pellets are finally discharged through the discharge hopper at a controlled rate to a product load-out system.

Limonite Iron Ore

Limonite is another ore of iron, this time with a chemical formula of FeO(OH)·nH2O, although it can be rather variable in compositions so could have other formulas, and is not considered a true mineral because of the variability of structure and is a mixture of other minerals.  A lot of what is considered Limonite is actually Geothite, an iron oxide which is the most common component of iron rust.  It is named after the Greek word for meadow as it is sometimes found in bogs and marshes.  As such is also otherwise known as bog ore.  The ore is quite dense and hardness is within the range of 4 to 5.5, so somewhat lower than Magnetite and the specific gravity is between 2.9 and 4.3, which is slightly higher than average.  It ranges in colour from bright yellow to greyish brown but generally looks brownish on a white background.

The mineral is sometimes formed from the hydration of both Hematite and Magnetite; from the chemical weathering of other minerals rich in iron or from the hydration of iron rich sulphide minerals.   It is always formed due to the alteration or solution of previously existing iron minerals and therefore, it is often found in the run-off streams from iron ore mines. Limonite is very common worldwide with deposits notable in China, Italy, Spain and the US.

Limonite can be used in the production of iron and steel but this is much less common than for both Hematite and Magnetite.  It has been known to contain Nickel, however, and some producers have used the ore to make stainless steel.  It has been used extensively as a pigment in the past, forming yellow to brown hues and can still be used as a colouration in paints of other dyes.  It has also been used for prospecting as it can sometimes signify the presence of gold ore.

Magnetite Iron Ore

Magnetite, otherwise known as Ferrous-Ferric Oxide or Magnetic iron ore is the other main ore of iron, in addition to Hematite, and has a chemical formula of Fe3O4. It was named after the Magnesia region of Thessaly, Greece and the word “magnet” actually comes from the mineral rather than vice versa.  Another story was that Magnes, a Greek shepherd, first discovered the mineral when he noticed that the nails of his shoe stuck to a rock.   It is the most magnetic naturally occurring mineral found on earth and small pieces of the ore can become magnetised naturally and will attract bits of iron which is how magnetism itself was originally discovered.  Small grains of Magnetite are found in most igneous and metamorphic rock and is also, less commonly, present in some sedimentary rock, sometimes in banded iron formations.  In appearance, it is a black, opaque, submetallic to metallic mineral and has a Mohs hardness between 5.5 and 6.5. It is often found in the form of isometric crystals.

The magnetic nature of the ore has led to lodestones, the naturally magnetised version of the mineral, to be used in early compasses.  It has also been useful in helping people understand the conditions under which rocks form and the movement of plate tectonics because the particles that it is made up of orient themselves in the direction of the earth’s magnetic field when magnetite is created in igneous and sedimentary rock so changes in the field over time can be studied by looking at the orientation of magnetic particles over time.  As well as being an ore of iron, it can also be used as an abrasive – Emery is a mix of magnetite and corundum, for example.  The ore is also used in industry, as a catalyst in the industrial synthesis of Ammonia and as a coating for steam boilers due to its stability at high temperatures.  It can also be used as a sorbent to remove Arsenic from drinking water.  Other uses include being used as a toner in electrophotography, as a micronutrient in fertilizers, as a pigment in paints, and as an aggregate in high-density concrete.

Magnetite is a commonly found mineral and in addition to the mineral rock form, it is also found as a black sand when it is eroded by rivers and deposited on a beach.  Black sand is notably present in New Zealand and California.  Magnetite does have a lower iron content than Hematite which means it has to undergo more processing to make it suitable for steel making. The magnetic properties of the ore means that it is particularly suitable for the further processing of iron ore into iron ore pellets or refined into concentrate, however.  While it is generally a lower-grade deposit, it is globally accepted as a viable and high-quality feedstock for the production of premium quality, low impurity steel.  The processing route for the ore requires crushing, screening, grinding, magnetic separation, filtering and drying.  After this processing, however, this ore does end up having a higher iron content than benchmark direct shipping ore  which means that iron ore sellers can recoup some of the extra costs associated with the higher processing required comparative to hematite.

Photo credit to R.Weller/Cochise College.

Hematite Iron Ore

cc hematite 3

There are several types of iron ore.  The most commonly mined type is Hematite, particularly in Brazil, China and Australia, where it makes up 96% of all exports.  The ore itself is a deep, brownish red colour which is where the name comes from (Haima is the Greek word for blood) and has a chemical formula of Fe2O3 and is also known as Ferric Oxide.  Hematite has a very high iron content, which can makes up about 70% of the ore but it can also contain quite a substantial amount of penalty elements such as Phosphorous, Aluminium and Water.  These high grade ores are also known as direct shipping ores because they are mined and extracted with a simple crushing and screening process before being loaded on to a ship for export, in contrast to Magnetite, the other main type of iron ore that has to undergo a further round of processing before it can be used.  This relatively simple extraction process also means that it is more time and cost efficient to mine than other types.

The large deposits of Hematite are extracted from altered banded iron formations and rarely igneous accumulations.  It is typically found in places where there has been standing water or hot springs where it can precipitate out of the water and collect in layers at the bottom of lakes or other slow moving water features.  Small crystals can also occur due to the weathering process of soils.  It is possible for the mineral to occur without the appearance of water, too, usually as a result of volcanic activity.  Interestingly, our planet is not the only one where Hematite has been discovered and two very large deposits have been found at the Terra Meridiani and Aram Chaos on Mars. The discovery was followed up by a Mars Exploration Rover and was found to be in the form of small sperules which analysis showed were concretions formed from a water solution which is clearly a significant discovery that suggest water was present on Mars at one time.

Obviously as an ore of iron, Hematite is mostly used in the production of iron and then used in the steel industry.  There are other uses for the mineral, however, and Ochre is often made up of between 20% and 70% Hematite.  Ochre has been used for many thousands of years as a dye and pigment.  Indeed much of the old cave paintings use Ochre as colouration and mines have been found going back some 7,000 years.  The mineral can also be used as jewelry and was probably at the height of its popularity in Victorian era Europe but there has recently been a bit of a resurgence in use as jewelry in the United States.  It has even been thought to possess healing powers and some people use it in Feng Shui and it is also used as a paint pigment.

Australia Iron Ore Exports Q1 to Q3 2012

 

The largest Iron Ore exporter in the world continues to provide a greater tonnage year on year for the first 9 months of 2012.

1 CHINA 270.5 MT +18%
2 JAPAN 60.5 MT 0%
3 SOUTH KOREA 37.3 MT +2%
4 TAIWAN 9.6 MT -3%
5 NETHERLANDS 0.5 MT -24%
6 INDIA 0.3 MT NEW
7 GERMANY 0.2 MT NEW
8 UTD ARAB EMIRATES 0.1 MT NEW
TOTAL 379.1 MT +13%

We can see that this growth is mainly driven by increased exports to China and this is by far the largest destination for Australian ore.  Deliveries to the other large Asian steel producers are fairly stable and a reduction in shipments to Rotterdam is counteracted by some new destinations.

Brazil Exports of Iron Ore – Q1 2012

The first quarter of 2012 has seen quite a dip in the exports of Iron Ore from Brazil.  In total, 68.4MT were exported, which is 26.9% lower than in the last quarter of 2011.  The largest destinations were:

1 CHINA 35.9 MT -24.8%
2 JAPAN 6.1 MT -47.7%
3 SOUTH KOREA 2.9 MT -37.3%
4 NETHERLANDS 2.5 MT -37.2%
5 GERMANY 2.3 MT -36.3%
6 ITALY 1.9 MT -40.9%
7 PHILIPPINES 1.8 MT 75.7%
8 OMAN 1.7 MT -6.3%
9 TAIWAN 1.6 MT 7.3%
10 ARGENTINA 1.5 MT -24.1%

So, almost all markets have reduced, with only the Philippines and Taiwan up on last quarter. A lot of the tonnage to Oman is for the large DRI plant located there.

Chinese Imports of Iron Ore – Q1 2012

Chinese imports of iron ore for the first quarter of 2012 were 187 MT, which is a record high for the largest importer in the world and is 5% up from the last quarter.  The top 10 origin countries were:

1 AUSTRALIA 83.0 MT +1.1%
2 BRAZIL 41.6 MT +9.3%
3 INDIA 14.1 MT +21.6%
4 SOUTH AFRICA 10.2 MT +4.4%
5 CANADA 5.5 MT +42.9%
6 UKRAINE 4.0 MT +19.3%
7 INDONESIA 3.9 MT +20.7%
8 IRAN 3.9 MT +7.4%
9 RUSSIA 3.3 MT -10.1%
10 PERU 1.9 MT -21.1%

Those percentages are compared to the last quarter (Q4 2011), when compared the the start of 2011 the imports from India have fallen 47% with the slack taken up predominantly by imports from Australia.  Imports from Iran, Russia and Peru also fell when compared to the same quarter of 2011.

Iron Ore Prices & News – 17 Apr 2012

The latest recorded Chinese spot prices of iron ore are as follows:

  • Aus Pilbara Fines   $148/tonne
  • Yandi Fines  $135/tonne
  • Indian Fines   $151/tonne
  • Iron Ore benchmark  $149.30/tonne

These prices remain historically high, and the benchmark price is the highest since mid October.  There is a general weakening of the spot price, however due to concerns over the slowdown of the Chinese economy which is growing at its slowest rate in recent times.  There is also a sign that steel makers are looking to run down some of their stocks and that the current spot price is considered rather high.  There is currently 97.6MT of stockpiled iron ore at Chinese ports.

The price for Indian ore remains high because of the perceived risk of disruption from the impending monsoon season.  The level of exports to the biggest market from India has dropped in the first part of 2012, however.