HOW IS ALUMINIUM MADE?

Step 1: Mining Bauxite

The journey begins with bauxite, an ore that contains a high percentage of aluminium hydroxide. Bauxite is primarily found in tropical and subtropical regions, with major deposits located in Australia, Guinea, Brazil, and Jamaica.

Mining bauxite involves several steps:

Exploration and mine development: Geologists identify bauxite deposits through various techniques, including aerial surveys and drilling. Once a viable deposit is located, mining operations are set up.

Extraction: The topsoil and overburden are removed to expose the bauxite ore. The ore is then extracted using methods such as open-pit mining or strip mining.

Crushing and washing: The extracted bauxite is crushed into smaller pieces and washed to remove impurities like silica, clay, and iron oxides.

Step 2: Refining Bauxite to Alumina

Once mined, bauxite is transported to refineries where it undergoes the Bayer Process to convert it into ‘alumina’ (aluminium oxide), which is the primary raw material for aluminium production and then the following processes are applied:

Crushing and grinding: The bauxite is further crushed and ground into a fine powder to increase the surface area for the chemical reaction.

Digestion: The powdered bauxite is mixed with a hot solution of sodium hydroxide. This caustic soda solution dissolves the aluminium hydroxide in the bauxite, forming a sodium aluminate solution.

Clarification: The solution is allowed to settle, and the undissolved impurities, known as red mud, are removed. The clear sodium aluminate solution is then decanted.

Precipitation: The sodium aluminate solution is cooled and seeded with aluminium hydroxide crystals. This induces the precipitation of aluminium hydroxide from the solution.

Calcination: The aluminium hydroxide precipitate is filtered, washed, and heated in rotary kilns or fluidized bed calciners at temperatures around 1000°C to remove water molecules, resulting in anhydrous alumina.

Step 3: Smelting Alumina to Produce Aluminium

Smelting simply means extracting metal from its ore by a process involving heating and melting. This is accomplished through the Hall-Héroult process (named after its inventors, Charles Martin Hall and Paul Héroult) which is an industrial method for extracting aluminium by electrolyzing molten aluminium oxide (alumina) dissolved in molten cryolite. This can be further explained through the following steps:

Electrolytic cells: The alumina is dissolved in molten cryolite (a sodium-aluminium fluoride compound) inside electrolytic cells or pots. These cells are lined with carbon, which serves as the cathode.

Electrolysis: A powerful electric current is passed through the cell. The electrical energy causes the alumina to dissociate into aluminium and oxygen ions. The aluminium ions migrate to the cathode, where they gain electrons and form molten aluminium.

Collection: The molten aluminium, being denser than the electrolyte, sinks to the bottom of the cell. It is periodically siphoned off and cast into moulds.

Step 4: Casting and Fabrication

The extracted molten aluminium is cast into various forms depending on its intended use. Common forms include ingots, billets, and slabs.

Primary casting: The molten aluminium is poured into moulds to form ingots, which are large blocks of aluminium. Ingots are further processed into different shapes and sizes.

Secondary processing: The ingots are heated and rolled into sheets, extruded into profiles, or drawn into wires. These processes involve a combination of mechanical and thermal treatments to achieve the desired physical properties.

Alloying: To enhance specific properties, pure aluminium is often alloyed with other elements such as copper, magnesium, manganese, silicon, and zinc. These alloys improve strength, durability, and other characteristics.

Step 5: Finishing and Recycling

The final stage in aluminium production involves fabrication, finishing treatments and recycling.

Fabrication: Aluminium sheets, profiles, and wires are fabricated into finished products through cutting, bending, welding, and assembly processes.

Surface treatments: Depending on the application, aluminium products may undergo surface treatments such as powder coating to enhance corrosion resistance, appearance, and other properties.

Recycling: Aluminium is highly recyclable, and recycling aluminium consumes only about 5% of the energy required to produce primary aluminium. Scrap aluminium is collected, melted, and cast into new products, contributing to a sustainable production cycle.

We hope our blog has given you a deeper insight into the journey of aluminium - from bauxite ore to finished product – and a deeper appreciation for the complex and energy-intensive process, involving multiple stages of extraction, refining, smelting, casting, and fabrication!

Each step is crucial in transforming raw materials into the versatile metal that is integral to modern industry and everyday life. As technology advances and the demand for sustainable practices grows, we’ll continue to innovate, striving for more efficient and environmentally friendly production methods in our facility.

For more information on how our fabrication service and how we can meet your aluminium extrusion needs, please contact us. We look forward to hearing from you.