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Friday, June 1, 2007

The Blast Furnace:

Blast furnace is a type of metallurgical furnace used for smelting to produce metals, generally iron.

In a blast furnace, fuel and ore are continuously supplied through the top of the furnace, while air (or pure oxygen) is blown into the bottom of the chamber, so that the chemical reactions take place throughout the furnace as the material moves downward. The end products are usually molten metal and slag phases tapped from the bottom, and flue gases exiting from the top of the furnace.

According to this broad definition, bloomeries for iron, blowing houses for tin and smelt mills for lead would be classified as blast furnaces. However, the term has usually been limited to those used for smelting iron ore to produce pig iron, an intermediate material used in the production of commercial iron and steel.

How it works: The Blast Furnace:

The purpose of a blast furnace is to chemically reduce and physically convert iron oxides into liquid iron called "hot metal". The blast furnace is a huge, steel stack lined with refractory brick, where iron ore, coke and limestone are dumped into the top, and preheated air is blown into the bottom. The raw materials require 6 to 8 hours to descend to the bottom of the furnace where they become the final product of liquid slag and liquid iron. These liquid products are drained from the furnace at regular intervals. The hot air that was blown into the bottom of the furnace ascends to the top in 6 to 8 seconds after going through numerous chemical reactions. Once a blast furnace is started it will continuously run for four to ten years with only short stops to perform planned maintenance.

The Process :

Iron oxides can come to the blast furnace plant in the form of raw ore, pellets or sinter. The raw ore is removed from the earth and sized into pieces that range from 0.5 to 1.5 inches. This ore is either Hematite (Fe2O3) or Magnetite (Fe3O4) and the iron content ranges from 50% to 70%. This iron rich ore can be charged directly into a blast furnace without any further processing. Iron ore that contains a lower iron content must be processed or beneficiated to increase its iron content. Pellets are produced from this lower iron content ore. This ore is crushed and ground into a powder so the waste material called gangue can be removed. The remaining iron-rich powder is rolled into balls and fired in a furnace to produce strong, marble-sized pellets that contain 60% to 65% iron. Sinter is produced from fine raw ore, small coke, sand-sized limestone and numerous other steel plant waste materials that contain some iron. These fine materials are proportioned to obtain a desired product chemistry then mixed together. This raw material mix is then placed on a sintering strand, which is similar to a steel conveyor belt, where it is ignited by gas fired furnace and fused by the heat from the coke fines into larger size pieces that are from 0.5 to 2.0 inches. The iron ore, pellets and sinter then become the liquid iron produced in the blast furnace with any of their remaining impurities going to the liquid slag.

The final raw material in the ironmaking process in limestone. The limestone is removed from the earth by blasting with explosives. It is then crushed and screened to a size that ranges from 0.5 inch to 1.5 inch to become blast furnace flux . This flux can be pure high calcium limestone, dolomitic limestone containing magnesia or a blend of the two types of limestone.

Since the limestone is melted to become the slag which removes sulphur and other impurities, the blast furnace operator may blend the different stones to produce the desired slag chemistry to create optimum properties such as has a low melting point and a high fluidity.
All of the raw materials are stored in an ore field and transferred to the stockhouse before charging. Once these materials are charged into the furnace top, they go through numerous chemical and physical reactions while descending to the bottom of the furnace.
The iron ore, pellets and sinter are reduced which simply means the oxygen in the iron oxides is removed by a series of chemical reactions.
At the same time the iron oxides are going through these purifying reactions, they are also beginning to soften then melt and finally trickle as liquid iron through the coke to the bottom of the furnace. The coke descends to the bottom of the furnace to the level where the preheated air or hot blast enters the blast furnace. The coke is ignited by this hot blast and immediately reacts to generate heat.

Since the reaction takes place in the presence of excess carbon at a high temperature the carbon dioxide is reduced to carbon monoxide.
The product of this reaction, carbon monoxide, is necessary to reduce the iron ore as seen in the previous iron oxide reactions.
The limestone descends in the blast furnace and remains a solid while going through it s first reaction.

This reaction requires energy and starts at about 875°C. The CaO formed from this reaction is used to remove sulphur from the iron which is necessary before the hot metal becomes steel.


This article was prepared by John A. Ricketts, Ispat Inland, Inc.

This article is based on proprietary information kindly supplied by:-

ATSI Engineering

415 Commerce

Dr.Amherst NYUSA

Red Hills :Rocks and Minerals

The rugged topography of the Red Hills doesn't fit the stereotypical portrait of the Kansas landscape. Located in southern Kansas, mostly in Clark, Comanche, and Barber counties, the Red Hills are part of the Permian deposits that geologists call red beds. They get their color from iron oxide (rust), which turns bright red when exposed to oxygen.
During the latter part of the Permian Period, about 260 million years ago, several thousand feet of brick-red shales, siltstones, and sandstones--along with interbedded layers of gypsum and dolomite--were deposited in Kansas. These Permian deposits have been exposed by erosion along the southern border of the state, forming a series of relatively flat-topped red hills, capped by light-colored gypsum or dolomite.

Source:Kansas Geological Survey staff,April 1999

Sunday, May 27, 2007

ITALY’s Red Ochre; Umber, Earthbrown, Brown Ochre

Due to contain iron and manganiferous clay or tone, Umber’s colour is brown. As manganese content increase, brown colouring also increases. This type of Umber brown ochre’s brown ground found in Italy, Cyprus, and flat country Netherlands.

RED PIGMENT : Red Ochre / Red Earths

RED PIGMENT Name : Red Earths / Red Ochre

Composition : Iron(III) oxide chromophore (Fe2O3 + clay + silica)

Band Wavenumbersa / cm-1 and Relative Intensities b: 220vs; 286vs; 402m; 491w; 601w
Excitation Wavelength and Power : 632.8 nm 3 mW
Hematite : Hematite has the formulae Fe2O3.

It has a relative hardness of 7.It is the most abundant and important ore or iron.

OCHRES are the natural mineral pigments occurring in various shades and colours, generally ranging from yellow to red to brown. The colouring power is mainly due to oxides of iron. They are also called 'coloured earths'. Ochre is a colouring mineral. The hydrous iron oxide imparts yellow colour and the unhydrous red colour. The amount of iron oxide (Fe2O3) in ochre is quite variable. It may be as low as about 20%, going up to 70%. The natural mineral pigment dominates in the market because of its cheapness, abundance in occurrence and good pigmentary quality. Depending upon the colour, the ochres are called red ochre, yellow ochre, green earths, sienna, umber etc.

In addition to red ochre, the red oxide of iron, commonly called 'red oxide', is an important natural pigment. It results from the alteration of hematite and ferruginous laterite and consists essentially of Fe2O3 having pigmentary quality.

Red oxide usually contains about 70% Fe2O3 . Sienna is a brownish yellow containing about 60% Fe2O3 with some quantity of manganese oxide. Due to a huge deposit located in Sienna in Italy it is called as Sienna. Sienna is marketed in the raw and burnt (calcined) states. The colour of the latter is brownish red.

Umber is named after A Central Italy based department first tested Red Ochre so it was name in Umber.Umber is a greenish brown containing some 45% Fe2O3 and 15% MnO2. Umber of good quality, called Turkish Umber, is found on the island of Cyprus. Numerous deposits of colouring earths occur in various parts of the world. Preparation of pigments from red oxide requires an elaborate process. Since it is hard, it has to undergo milling and finally separation of the coarse particles by elutriation.

Ochres being friable are crushed and lixivated, just like china-clay, to obtain extremely fine-textured material of uniform colour. Refining by elutriation followed by drying often improves both iron content and colour.

Application or uses of Ochres: Mainly its use is as tinting colours and for colour washes, distemper and oil paints. It is also used in making coloured paper. For this particular use ochre and china-clay or soapstone, after dissolving in water in paste form, are acreened and added in the beater for the preparation of coloured paper pulp. Red oxide pigments are widely used as primers for painting structural steel, automobile bodies, ship bottoms, etc.
Properties of Ochres: The staining power, brilliance and fineness of texture are the main properties by which an ochre is judged for its quality and value in industry. The tint should be wholly of the inorganic ingredient.

Occurrence in Persian Gulf and Spain : The highest red oxides are found along the Persian Gulf and in Spain. The Persian deposit is mined on the Omur island. A brown oxide found in Pennsylvania, USA, is known as 'metallic brown'.

Pigment Information :Ochre is a natural earth containing silica and clay tinted by hydrous forms of iron oxide, such as yellow-brown limonite or brown-yellow to green-yellow goethite, and traces of gypsum or manganese carbonate. Limonite is a general term used to describe all forms of hydrated iron oxide minerals (FeO(OH)) that occur as natural clay or earth.
Limonite includes the minerals goethite, akaganeite and lepidocrocite. To be considered an ochre, the content of iron oxide must not be less than 12%. Depending upon the content of hydrated iron oxide, the color of ochre varies from light yellow to golden to orange.
The higher the content of iron oxide in an ochre the greater its tinting strength and hiding power. Most yellow ochres are normally not calcined as heat does relatively little to alter their color. Like red iron oxides (hematite), they are found around the world and have been used as pigments since prehistory. French ochre, historically one of the best grades of limonite, contains about 20% iron oxide and is high in silica. In Russia, high quality ochres can be obtained from the Izyumskyy deposit in Ukraine, and the Zhuravskoye, Skarnovskoye and Dubovikovskoye deposits in the Voronezh region, and the Lyubytinskoye deposit near Novgorod.

Oil Absorption and Grinding: Ochre absorbs a medium amount of oil. It slows the drying of oil paint, but forms an excellent film.
Toxicity : Ochre is not considered toxic, but care should be used in handling the dry powder pigment to avoid inhaling the dust.Ochre, Gold :Gold ochre is a natural earth containing clay tinted by hydrated iron oxide, such as yellow-brown limonite or brown-yellow to green-yellow goethite. Ochre, Warm Red :Warm red ochre is a natural earth containing clay tinted by hydrated iron oxide that gives an exceptionally warm orange red hue.