Extraction of Iron Ore

Extraction of Iron-ore :

Before many ancient civilizations began to transition from their bronze age to an iron age, some toolmakers were already creating iron implements from a cosmic source: meteorites. Called 'black copper" by the Egyptians, meteoric iron isn't the sort of substance one finds in huge, consolidated locations. Rather, craftsmen found bits and pieces of it spread across great distances. As such, this heavenly me

tal was mostly used in jewelry and ornamentation. While blacksmiths occasionally used meteoric iron to craft swords, these prized weapons were usually relegated to men of great power, such as the seventh century Caliphs, whose blades were said to have been forged from the same material as the Holy Black Stone of Mecca.

The majority of Earth's iron, however, exists in iron ore. Mined right out of the ground, raw ore is mix of ore proper and loose earth called gangue. The ore prop

er can usually be separated by crushing the raw ore and simply washing away the lighter soil. Breaking down the ore proper is more difficult, however, as it is a chemical compound of carbonates, hydrates, oxides, silicates, sulfides and various impurities.

To get to the bits of iron in the ore, you have to smelt it out. Smelting involves heating up ore until the metal becomes spongy and the chemical compounds in the ore begin to break down. Most important, it releases oxygen from the iron ore, which makes up a high percentage of common iron ores.

The most primitive facility used to smelt iron is a bloomery. There, a blacksmith burns charcoal with iron ore and a good supply of oxygen (provided by a bellows or blower). Charcoal is essentially pure carbon. The carbon combines with oxygen to create carbon dioxide and carbon monoxide (releasing lots of heat in the process). Carbon and carbon monoxide combine with the oxygen in the iron ore and carry it away, leaving iron metal.

In a bloomery, the fire doesn't get hot enough to melt the iron completely. Instead, the iron heats up into a spongy mass containing iron an

d silicates from the ore. Heating and hammering this mass (called the bloom) forces impurities out and mixes the glassy silicates into the iron metal to create wrought iron. Wrought iron is hardy and easy to work, making it perfect for creating tools.

Tool and weapon makers learned to smelt copper long before iron became the dominant metal. Archeological evidence suggests that blacksmiths in the Middle East were smelting iron as early as 2500 B.C., though it would be more than a thousand years before iron became the dominant metal in the region.

To create higher qualities of iron, blacksmiths would require better furnaces. The technology gradually developed over the centuries. By the mid-1300s, taller furnaces and manually operated bellows allowed European furnaces to burn hot enough to not just soften iron, but actually melt it.

Processing of steel :

The more advanced way to smelt iron is in a blast furnace. A blast furnace is charged with iron ore, charcoal or coke (coke is charcoal made from coal) and limestone (CaCO3 ). Huge quantities of air blast in at the bottom of the furnace, and the calcium in the limestone combines with the silicates to form slag. Liquid iron collects at the bottom of the blast furnace, underneath a layer of slag. The blacksmith periodically lets the liquid iron flow out and cool.

At this point, the liquid iron typically flows through a channel and into a bed of sand. Once it cools, this metal is known as pig iron. To create a ton of pig iron, you start with 2 tons (1.8 metric tons) of ore, 1 ton of coke (0.9 metric tons) and a half ton (0.45 metric tons) of limestone. The fire consumes 5 tons (4.5 metric tons) of air. The temperature at the core of the blast furnace reaches nearly 3,000 degrees F (about 1,600 degrees C).

Iron Advantage

Between the 15th and 20th centuries, some countries had an industrial leg up on the competition due to the availability of iron ore deposits. For example, China, India, England, the United States, France, Germany, Spain and Russia all have substantial iron ore deposits. When you think of the historical importance of all of these countries, you can see the correlation!

Pig iron contains 4 to 5 percent carbon and is so hard and brittle that it's almost useless. If you want to do anything with it, you have three options. First, you can melt it, mix it with slag and hammer it out to eliminate most of the carbon (down to 0.3 percent) and create strong, malleable wrought iron. The second option is to melt the pig iron and combine it with scrap iron, smelt out impurities and add alloys to form cast iron. This metal contains 2 to 4 percent carbon, along with quantities of silicon, manganese and trace impurities. Cast iron, as the name implies, is typically cast into molds to form a wide variety of parts and products.