Metal is an elementary substance, usually lustrous, malleable and ductile, has basic oxides and forms positive ions; is a good conductor of heat and electricity.
All metals can be repeatedly recycled, though some are much more valuable than others!
Recycling other metal items
Scrap metal dealers are listed in the Yellow Pages – they will pay for most clean metals depending on the international markets, and pay less if they collect rather than you deliver.
Mining for metal requires considerable energy use, causes land disturbance and erosion, air and water pollution. The most noticeable damage is land scarring and thereby habitat loss.
Metalworking involves welding, cutting and surface finishing of metals and creates hazards in the form of metal dust, welding fumes, gases containing metal and metal cleaners and degreasers, which usually contain organic solvents.
Closing the loop...steel to steel recycling
Scrap steel is the primary ingredient in steel making today. There are two types of steel making processes: the basic oxygen furnace (BOF) which will consume a minimum of 25% scrap steel to make new steel; and the electric arc furnace, which can use virtually 100% scrap steel. The basic oxygen furnace is used to make steel for cans. The BOF melts the metal to form liquid steel that is cast into slabs and hot strip rolled into coils. The coils are cleaned and cold rolled into sheets that are suitable for applying tin to. The end product is called tin plate, - the tin stops the steel from corroding.
In the recycling process, the cans are put into a huge container with holes in the bottom. This container is immersed in a caustic solution which dissolves the tin from the cans. The steel is washed and sold as high grade steel, while the tin is removed from the caustic soda by electrolysis and made into ingots which are sold to companies needing tin.
The Steel industry globally recovers about 65% of all steel produced. Most existing steel products represent an inventory of resources available for new steel production. There is no limit to the number of times steel can be recycled – today’s food can is tomorrow’s car.
Improved design and technology has seen the amount of metal used in products decrease significantly: aluminium drink cans weigh 40% less than they did a decade ago, and while a certain sized office building may have used 100,000 tonnes of steel 30 years ago, it will now use only 35,000 tonnes.
Aluminium is made from bauxite, a non-renewable resource. Most bauxite is mined from just under the forest floor in tropical and subtropical forests of the world. Mining requires the complete destruction of the forest as the bauxite is found just under the forest floor. This deforestation leads to devastating floods, mud and landslides, as the trees are no longer there to absorb the vast quantities of water in the tropics.
From 1 tonne of bauxite, 500kgs waste and 500kgs of aluminium are produced.
Process: Making aluminium
Bauxite is generally a mixture of aluminium oxides, iron oxides and clay. The first stage is to remove alumina (a white sandy powder consisting of aluminium oxide) from the bauxite by dissolving it in liquid caustic. The residues, which are insoluble in the caustic, are removed and collected. These residues are used as mud brick or as aggregate for road foundations.
The alumina is then removed from the liquid caustic. The solution is cooled until crystals form, the crystals are then washed, dried and sent to smelters. The final stage is smelting the alumina into metal. Smelting is the process of removing oxygen from the alumina to produce pure aluminium. Smelting takes place in furnaces known as reduction cells. The alumina is fed into a reduction cell at high temperatures along with sodium aluminium fluoride, known as cryolite. An electric current is passed through the mixture, splitting the oxygen from the alumina and leaving the molten aluminium metal. Pure molten aluminium is cast into ingots, which can be made into a variety of products.
Making new aluminium from old is known as secondary aluminium production. In this process, recovered aluminium is melted in a furnace and mixed with other material to form an alloy. Primary (virgin) aluminium is also added to meet industry specifications for end use products. After heating, the molten mixture is then cast into ingots, sheets or aluminium products.
Benefits of Recycling Aluminium
- Metal recyclers will pay per kg of aluminium – 1 kg is about 50 cans.
- Recycling aluminium literally saves tropical forests from destruction by mining for bauxite.
- Using old cans to make new saves 95% of the energy needed to make the new can from ore.
- Recycling one can saves enough energy to run a TV or computer for 3 hours.
- Aluminium does not degrade during recycling, so it can be used over and over again.
Way back when...the history of metal
It is thought that metal was discovered when glistening liquid oozed from rocks heated by fire. On cooling, the liquid solidified into metal, and man was quick to discover how useful metals are for tools, weapons and ornaments. Copper was used in the Middle East as early as 4000BC.