METALLURGY – 2Metals are extracted from their ores. Ores contain all unwanted impurities and a part of required

metal too. Metallurgy is the process of extraction of purest

form of metals which include both physical and chemical process.

But First,Let us go through an interesting statement, Nernst Distribution

Law

A man named NERNST stated a law which helped people to explain this concept easily. His statement was,

“When a solute is dissolved in a mixture of two non mixing solvents, the solute distributes itself in the two solvent so that the ratio of conc. of the solute in the solvents is constant at constant temperature.” This is nothing but distribution co efficient or partition co efficient. If you didn’t understand, replace all solute by salt, all solvents by water and oil and Imagine.

Silver :Parke’s Process

As the diagram indicates, Parke’s process is as simple.

The Argentiferrous lead containing traces of silver is heated to 1073K and melted. It is then mixed with molten zinc. These two liquids do not mix. Hence, the two liquids form two different layers in the container. Since the Silver is 300 times more soluble in Molten zinc, most of Silver moves upwards leaving lead behind. On cooling the mixture of molten zinc and silver, It turns into solid and is skimmed off. The remaining molten lead is added to more zinc and the process is repeated till there is no trace of silver in it. The Zn, Ag alloy is distilled. Zn melts easily and is removed. The remaining Ag contains only lead impurities and can be removed with the process of cupellation.

Ellingham Diagrams

Definition for Ellingham Diagrams

They are the graphs that indicate the variation of Standard free energy changes as function of temperature for the formation of oxides, chlorides or sulphides of various elements.

Now let us learn a bit about its characteristic features. Its just easy to understand but a very too difficult task to memorize…

The graphs for the formation of metal oxides always slope upwards.

There is a sudden change in the slope of the graphs at temperatures like melting points or boiling pints.

For metals like Ag and Hg, the variation of Standard free energy change for the formation of their oxides becomes greater than 0 at higher temperatures.

Any metal oxide with lower standard free energy change is more stable than another metal oxide with higher standard free energy change

In the diagram, the graph for the formation of CO shows negative slopes.

Limitations of Ellingham Diagrams

The reactants and products are considered to be in equilibrium which is not true.

These graphs explain the spontaneity of a reaction but not the rate of a reaction

Extraction of Iron from Its ore

Iron is extracted by a device called blast furnace.

It is usually available in the form of haematite ore. Because It is abundantly found in haematite ore.

Blast furnaceCup and cone arrangement

Tuyers

Blast furnace is a tall cylindricalTower made up of steel platesWith a lining of fire bricks.The widest part of the furnaceIs called Boshes. Hot air isBlasted into the furnace belowThe boshes through water cooledPipes called tuyeres.

400C

600C

900C

1200C

1500C

Process

Haematite ore is crushed and washed with a current of water to remove most gangue. The concentrated ore is then heated in the presence of limited supply of air (calcination). The moisture escapes and C, S, Arsenic etc. form their oxides. Any FeO present in the ore is oxidized to ferric oxide. There will be pores in the ore.

4FeO+O2 2Fe2O3

Smelting

A mixture of haematite ore, Limestone and coke in the ratio 8:1:4 is introduced into a blast furnace at its top by means of cup and double cone arrangement.

Coke burns in air to give CO2. The reaction is exothermic and temperature decreases to 1773K near the boshes. As CO2 rises up, it combines with more coke to give CO.

The reaction is endothermic and the temperature decreases as the gas moves up resulting in a gradual decrease of temperature from 1500C at the boshes to 400C at the top.

At 600C, ferric oxide is reduced by carbon monoxide to give Iron. The spongy Iron moves down through the hotter portions of the furnace. Hence it melts and collects at the bottom. It is known as cast iron which contains 2 to 4.5% carbon.

At 900C, limestone decomposes to give calcium oxide and CO2. CO2 moves up. The remaining calcium oxide combines with

silica impurity to form calcium silicate. Molten calcium silicate is lighter than molten iron. Hence it collects as a different layer.

Molten Iron and calcium silicate are removed through an outlet near the top.

That Is all about metallurgy.

Just leave a comment or suggestions for the hard work done.

Per Quanto Reguarda, Anshuman Rao