Chemistry - Metals From Rocks

Metal are found in rocks, some are quite common, aluminium, some are quite rare, copper. The metals are extremely difficult to extract. Some natural processes concentrate metals in cart rocks making them easy to extract, these are ores.

Open cast mining has the same problems and benefits as limestone quarrying (see rocks and building materials) and tunnelling down is more expensive and difficult. There are more pollution issues as the ores are toxic and only a fraction of the ore is useful so the rest is left in unsightly spoil tips.

To find out whether it is worth it depends on:

How concentrated is the ore.          How easy it is to get the ore from the ground.

How easy it is to extract the metal from the ore.          What financial profits would be made.          The long term environmental costs.

The price of the metal depends on its demand, it may have a high price one day, but then a very low price the next.

To extract the metal there are four stages:

• 1. The ore is mined through open cast mining or tunnelling down.
• 2. The ore is separated from impurities, these impurities are left as spoil tips that and often toxic, dissolves into the soil and kill plants.         
• 3. The ore is converted to the metal, this is usually by heating it with carbon forming carbon dioxide which contributes to global warming.
• 4. The metal is the purified.

Copper or aluminium can be used as useful products, wiring, bikes but when the product is worn out metals can be recycled. 

Recycling; 1. Saves money.     2. Reserve metals in the grounds last longer.     3. Avoids waste and pollution     4. Lessens the effect effects of mining of people and the environment.          5. Saves energy

A metal ore is goes to a concentrated ore with much waste, then made into an impure metal which is made pure and used. Then it is recycled making it an impure metal again.

The reactivity scale is like this, from least reactive to most reactive, Gold, Copper, Tin, Iron, Carbon, Aluminium, Magnesium.

Carbon is more reactive than some metals like iron and copper so it can displace these metals from their ore. When carbon, usually coal, displaces the metal from the ore it is also a redox reaction if the ore is an oxide, which many of them are.

When this reaction is performed in a furnace, carbon dioxide is given off as a gas and pure molten metal will flow out of the bottom.

Aluminium is expensive because it is more reactive than carbon is, therefore is extracted by other means.

These means are when aluminium is heated so it becomes molten and split from its ore through electrolysis.

This is very costly and uses large amounts of energy. 

Iron is the most used metal. We produce 1.5 billion tonnes yearly and is 20 times as much as the production of all metals put together.

This makes it cheap so even though aluminium is more common, iron is cheaper.

Iron is the most used metal but is not as easy to extract as metals like copper. Iron can only react with carbon at 1600 degrees in a blast furnace. The impurities of of the ore will react with limestone producing ****, it is unsightly and dangerous.

Copper is usually in copper sulphide crystals. Copper can be extracted through displacement using carbon, limestone is not needed but this is very expensive. However copper is increasingly difficult to find and inn these there are only 1%.

In one method of extraction, acid is sprayed on the rock, this dissolves the rock and the leachate is collected, the copper is then removed from the leachate through electrolysis. 

New methods that can be used in the future is bioleaching, which is when bacteria eat the copper ions and excrete copper-rich leachate, and phytomining, (see next card).

Mining is also very unethical as mines will be surrounded by waste heaps and will carry toxic metal salt into rivers.

Many metals are running out but most metals can be found in developing countries. We use these countries to extract the metals for low prices which has benefits, but there are many health risks.

Recycling makes our resources last longer and reduces pollution however it costs a lot. Recycling is only worth the money for difficult metals to extract, like aluminium and iron and steel.

We we mine, we contaminated land. Many plants can't grow on this land but brassicas not only thrive but absorb the metals. This has led to phytomining. 

As these plants grow they take in the metals cleaning the land, they are then harvested and burnt forming metal rich ash that can then be extracted.

The properties of metals are:

• Strong, making them good structural materials for machines, frameworks.
• Easy to shape, they can be bent, pressed, drawn and rolled making them good for car body panels.
• Metals have high melting points, engines won't melt when the get hot in use.
• Metals conduct heat and electricity, so can be used for wiring and heat sinks

The transition blocks on the periodic table, like iron and copper, contain every day metals. Iron can be made into hard and touch machinery or into an easily bendable material. It is extremely versatile but corrodes easily.

Copper is a good conductor of electricity, soft and bends. The best saucepans often have copper bottoms. It can also be used for pipes as it does not easily corrode however it is expensive.

Steel is great for cars trains and ships but is useless for air planes because it has too high a density and would take too much energy to get off the ground. Aluminium, however, can be used for planes, if added with 4% copper, to form a steel it will be stronger and is called duralumin. 

However, when aluminium wad used for a fighter jet, the heat could melt the aluminium.

Titanium was then used as a new super metal because it could with stand high temperatures, strong as steel and has a low density. Titanium would be used to replace steel but it is very expensive.

Both titanium and aluminium resist corrosion which is why aluminium foil stays shiny.

Titanium resists corrosion better than aluminium and stainless steel.

When iron comes out of the blast furnace it still has impurities such as carbon, sulphur and phosphorus. This makes the iron brittle and are removed by reacting them with oxygen forming oxides. The iron is then soft and easily shaped.

Most iron is then converted to steel. Steels are alloys. Steel is a mixture of iron, carbon or some other metals. Alloys are harder than iron.Steel is easily shaped and used for wire, nails and car bodies.

Carbon is added in calculations to design specific properties of the strength and hardness. Adding more carbon will make the steel harder and stronger but making it harder makes it harder to shaoe.

Once over 1% of carbon is in the steel, the strength will drop so they can be brittle, these metals are used for cutting tools, drill bits and masonry nails. These nails do not bend as easily as low carbon steel would however can snap if stuck incorrectly.

If nickel is added to steel then it becomes hard and strong and used for machinery, tungsten is added to make it very hard, which is used for cutting tools and adding chromium will make it stainless steel (does not corrode).