The Extraction Of Iron (Page 3 of 4) in pdf

used for things like manhole covers, guttering and drainpipes, cylinder blocks in car engines, Aga-type cookers, and very expensive

and very heavy cookware.

Steel

Most of the molten iron from a Blast Furnace is used to make one of a number of types of steel. There isn't just one substance called

steel - they are a family of alloys of iron with carbon or various metals. More about this later . . .

Steel-making: the basic oxygen process

Impurities in the iron from the Blast Furnace include carbon, sulfur, phosphorus and silicon. These have to be removed.

• Removal of sulfur:

Sulfur has to be removed first in a separate process. Magnesium powder is blown through the molten iron

and the sulphur reacts with it to form magnesium sulfide. This forms a slag on top of the iron and can be removed.

\[ Mg + S \rightarrow MgS \tag{7}\]

• Removal of carbon:

The still impure molten iron is mixed with scrap iron (from recycling) and oxygen is blown on to the mixture.

The oxygen reacts with the remaining impurities to form various oxides. The carbon forms carbon monoxide. Since this is a gas it

removes itself from the iron! This carbon monoxide can be cleaned and used as a fuel gas.

• Removal of other elements:

Elements like phosphorus and silicon react with the oxygen to form acidic oxides. These are

removed using quicklime (calcium oxide) which is added to the furnace during the oxygen blow. They react to form compounds

such as calcium silicate or calcium phosphate which form a slag on top of the iron.

Types of iron and steel

Cast iron has already been mentioned above. This section deals with the types of iron and steel which are produced as a result of the

steel-making process.

• Wrought iron:

If all the carbon is removed from the iron to give high purity iron, it is known as wrought iron. Wrought iron is

quite soft and easily worked and has little structural strength. It was once used to make decorative gates and railings, but these

days mild steel is normally used instead.

• Mild steel:

Mild steel is iron containing up to about 0.25% of carbon. The presence of the carbon makes the steel stronger and

harder than pure iron. The higher the percentage of carbon, the harder the steel becomes. Mild steel is used for lots of things -

nails, wire, car bodies, ship building, girders and bridges amongst others.

•

High carbon steel: High carbon steel contains up to about 1.5% of carbon. The presence of the extra carbon makes it very hard,

but it also makes it more brittle. High carbon steel is used for cutting tools and masonry nails (nails designed to be driven into

concrete blocks or brickwork without bending). You have to be careful with high carbon steel because it tends to fracture rather

than bend if you mistreat it.

•

Special steels

These are iron alloyed with other metals. For example:

iron mixed with

special properties

uses include

cutlery, cooking utensils,

kitchen sinks, industrial

stainless steel

chromium and nickel

resists corrosion

equipment for food and

drink processing

The Extraction Of Iron Page 3

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