Mode-AL and the Environment

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 ALUMINIUM

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.

BAUXITE

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.

ALUMINA (AL²O³)

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.

THE METAL

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.

RECYCLING

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 materials.

The recycling process uses 5% of the energy that was used when producing the primary aluminium.

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 lost.

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.

ENVIRONMENTAL EFFECTS

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.

ABSOLUTE RECYCLING

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 absolute recycling.

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 is achieved.

ENVIRONMENTAL EFFECTS 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 afterwards.

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 treatment plants.

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