Extraction and Uses of Metals

Very few metals exist as elements in nature. Most metals are combined with other elements and exist in the form of compounds known as metal ores.

A metal ore is a rock containing a mineral from which a useful metal is extracted. Metal ores in the form of sand/rock are frequently found. Only metals low in the reactivity series (e.g. silver and gold) are found in an uncombined state.

The lower the position of the metal in the reactivity series, the easier it is to extract from its ore.

There are two main methods to extract a metal from its ore: Electrolysis Chemical reduction, using carbon

Very reactive metals are most difficult to extract and cannot be reduced by carbon. Extracted by electrolysis of their molten ore as electricity is used to break up the strong bonds found in the compounds.

Moderately reactive metals are easier to extract. Middle of reactivity series and thus their oxides can be extracted by heating with carbon in a blast furnace.

The least reactive metals are the easiest to extract and are already found in the forms of elements

Metals are finite resources and can be rapidly depleted after continuous extraction. Thus there is a need to recycle metals or use other materials as substitutes.

Advantages of Recycling Metals Allows conservation of valuable metals such as gold and platinum. Cost of extracting metals are saved. Prevents waste of metals that cause land pollution and environmental problems.

Disadvantages of Recycling MetalsToo costly to recycle metals and thus is rarely carried out for most metals. Too difficult and costly to separate metals in alloys for recycling. Other metals such as lead are too expensive to extract and can cause pollution to damage the environment.

a) Extraction of Iron An important ore containing iron (III) oxide, Fe2O3, is hematite. Iron is extracted from hematite by reduction with carbon monoxide in a blast furnace.

Reactions taking place in the blast furnace. Iron ore and coke are fed into the blast furnace. Limestone (CaCO3) is also added to impurities like silicon dioxide. Blasts of hot air are sent in at the bottom of the furnace. First, coke burns in the presence of air to form carbon dioxide. (The heat produced helps to maintain the temperature of the furnace.) Carbon dioxide rises up to the furnace and reacts with more coke to form carbon monoxide. Note: Carbon Monoxide is the reducing agent which reduces hematite to iron. Hematite is reduced by carbon monoxide to form molten iron and carbon dioxide. The molten iron then sinks to the bottom of the furnace and tapped off at intervals. Iron produced is impure and contains mainly sand (silicon dioxide) which is removed by the addition of limestone to the furnace. Limestone decomposes by heat to form calcium oxide and carbon dioxide. Calcium oxide combines with the sand to form calcium silicate (slag). Molten iron and molten slag sink to the bottom of the furnace with the slag floating on top. Slag and iron rapped off separately and allowed to solidify.

b) Steel - an alloy of iron and carbon Is the most widely used alloy of iron and contains iron and carbon as well as other other metals. Steel is sturdier than aluminum alloys but its main disadvantage is that it is harder to separate.

High Carbon Steel: 0.6-.1.5% carbon Very strong, tough and hard, but brittle Used for springs,cutlery, tools

Medium Steel: 0.2-0.6% carbon Tough and hard Rails, girders

Mild Steel: Softer and more easily shaped, malleable and ductile Car bodies, cables, machinery, nails and chains

Stainless

Stainless Steel: Contains chromium, nickel  in addition to iron & carbon Does not rust or react with acids Very hard and heat resistant

High speed steel: Contains tungsten and vanadium in addition to iron & carbon Very hard & heat resistant High-speed drills

Extraction of Metals from Ores

Recycling of Metals

Iron