We at Mode-AL
recognise that if we all did our bit with regard to recycling,
then the world would be a much better place. We are doing
our bit by recycling all the aluminium scrap from our machining
processes back to our extrusion suppliers so it can be melted
and used again. Below is an extract from Sapa Profiles Ltd
showing the benefits of recycling aluminium from the humble
‘Coke’ can to our furniture. All of it can be
recycled; all you have to do is your bit.
FROM BAUXITE TO RECYCLABLE
There is plenty of raw
material for the production of aluminium. No less than 8%
of the crust of the earth consists of aluminium compounds
in many different forms.
The most important raw
material in the process of making aluminium is bauxite.
If we continue mining bauxite at the same rate as the present
one, the deposits of bauxite will last 200-400 years of
production (this does not include an increase in recycling).
Bauxite, which is created
when certain aluminium bearing rocks decompose, consists
of oxides of aluminium, iron and silicon.
The most important deposits
of bauxite are situated near the Equator. Brazil, Australia
and Jamaica. Surinam are big producers.
At first, the bauxite is
purified into alumina. The process of making bauxite into
alumina is often performed near a bauxite mine. The aluminium
is produced by an electrolysis of molten aloxite, as often
as possible this is done in countries with good access to
power supplies, often from hydroelectric power plants.
The production of 1kg of
aluminium requires approximately 2kg of alumina. The production
of 2kg of alumina requires 4kg of bauxite.
In the melting process,
1kg of metal requires approximately 47 MJ (app. 13kWh).
This is an investment. The use of energy will be justified
many times over when Aluminium is converted into many forms
e.g. When used in automotive application it results in reduced
consumption of fossil fuels.
Used aluminium products
have great importance as a raw material for production.
In principle, all available
aluminium can be recycled.
By sensible sorting, aluminium
scrap can be turned into new products over and over again.
Even though aluminium is used over and over again, its characteristics
never change which is unique in comparison to most other
The recycling process uses
5% of the energy that was used when producing the primary
The re-melting and recycling
of aluminium is becoming more and more important in today's
society of recycling.
EASY TO RECYCLE
Aluminium is the ideal
metal. In the re-melting process, only a few percent is
A better sorting of scrap
results in an increasing recycling percentage. Small quantities
end up in refuse disposal units. The metal is just as valuable
as black coal and carbonised coal regarding the process
of making energy. What is left over, becomes alumina.
All industrial activity
uses up natural resources and has an impact on the environment.
This also happens when producing aluminium. However, production
of aluminium often imposes a positive impact on the environment
compared with the use of alternative materials.
Life cycle analysis is
the only method which can be used to determine the comparative
impact on the environment.
Aluminium that is gathered
for recycling can circulate in an almost never-ending cycle
of operation. The loss of metal die to oxidation in the
melting process is small.
The quantity of the re-melted
material is so high that it can be used for the same product
over and over again.
Repeatable recycling is
possible without lowering the quality and with high yield
1* 1MJ = 0.278 KWH
2* The calculated use of energy asimens the anodised extrusions
have a surface area of 0.3m² / Kg
As mentioned before, the
manufacturing of aluminium from bauxite requires a lot of
energy but the process of turning an aluminium bar into
an extrusion requires relatively little energy. The tables
shows standard production units and embodies the total use
of energy including room hearing, internal transport etc.
If you use scrap as a raw
material, the use of energy does down from 134 to approximately
14 MJ/kg (from app. 37 to app. 4 kWh). At the same time,
a similar reduction in the emissions such as carbon dioxide,
carbon monoxide, nitric oxides, and sulphur oxides
OF EXTRUDING, SURFACE TREATING AND FABRICATING
The punching of extrusions
is the main source of noise in the factories. The noise
can be reduced by a noise reduction system.
By changing lubricants,
the condition of the air in the workshops is improved and
extrusions are cleaner. This reduces the need for cleaning
The dies are hardened by
gas nitriding. This procedure reduces the environmental
damage compared to the previously used procedures.
In mechanical fabrication,
mineral oil based cooling and cutting liquids were used.
These have been replaced by water based products. This resulted
in environmental improvements and a reduction in the demand
for organic solvents for degreasing.
Sapa has completely stopped
using trichloroethylene for degreasing. By degreasing with
water based solvents, droplets of grease and oil in the
shape of semi stable emulsion are produced. When emulsion
separates, the life of the degreasing bath is prolonged.
The etching process in
anodising has been improved by ‘long life’ baths.
This type of bath has a lower demand for chemicals and smaller
waste deposits to manage. Used etching baths are neutralised,
aluminium separating as hydroxide. This hydroxide is turned
into chloride and is used as a flocking chemical in water
Previously when dyeing
anodic oxide films, copper and cobalt oxides were used to
achieve the required colours. Today, tin oxides are used
and have lower toxicity.
With thanks to world-aluminium.org
for pictures and information