HOW OUR ALUMINIUM IS MADE
LEARN HOW OUR ALUMINIUM IS MADE
TIWAI POINT ALUMINIUM
“We turn pure water into pure aluminium. That’s just how we think.”
Tiwai is one of the few smelters in the world producing ultra-high purity aluminium, and the only one making it with a renewable energy source. Learn how an isolated smelter at the bottom of New Zealand makes aluminum that is used all around the world.
Bauxite ore is mined in Australia
Aluminium production begins with bauxite. This sedimentary rock is mined in North Queensland and Western Australia.
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Alumina is shipped to New Zealand
Bauxite is shipped to alumina refineries where it is refined through the Bayer process into alumina (aluminium oxide) – this fine, odourless, crystalline powder is then transported to Tiwai by ship.
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Alumina is converted to aluminium in New Zealand at Tiwai Point
When the alumina arrives at Tiwai wharf, it is transported to the reduction cells where the Hall-Heroult process begins and aluminium, with one of the lowest carbon footprints in the world, is produced.
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One of a kind
While smelting requires large amounts of electricity, Tiwai is the only smelter in the world producing ultra-high purity aluminium from a renewable energy source.
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Power from Manapōuri
Hydroelectricity, generated at Lake Manapōuri powers the electro-chemical reaction that turns alumina into aluminium.
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Powering the reduction cells
At full production Tiwai operates four reduction lines – Lines 1, 2 and 3 each contain 208 individual cells and Line 4 has 48 cells. Cells are connected in an electrical circuit with Lines 1, 2 and 3 operating with a constant electrical current of approximately...
199,000 amps
Lines 1, 2 and 3
232,000 amps
Lines 4
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The chemical reduction of alumina to aluminium
Large carbon blocks are transported via an Anode Transport Vehicle, and suspended into the reduction cells. These cells are lined with refractory bricks and carbon – meaning they can withstand heat and conduct the electrical current required for the smelting process. While much of these carbon blocks are consumed by the process, remnants are recycled and reused.
Alumina is fed into the individual cells at regular intervals, and dissolved in a bath of molten cryolite.
The electrical current passing through the alumina and cryolite solution causes an electro-chemical reaction producing aluminium and oxygen.
Oxygen is attracted to the carbon block (the anode) and the hot, molten aluminium accumulates at the carbon lining (the cathode).
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Emissions are controlled, recycled and cleaned
The individual cells in the reduction lines are fully enclosed to minimise the escape of untreated gases.
The reduction process generates fluoride gas, sulphur dioxide and carbon oxides. These dust particles and gases are drawn from the cells, through a system of ducts to 13 dry scrubbers, where alumina is mixed with the gas stream absorbing the fluorides at more than 99% effectiveness. The fluoride-enriched alumina is returned to the reduction cells while the cleaned gases are released into the atmosphere.
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Around 1.5 tonnes of molten aluminium is produced in each cell every 24 hours
The molten aluminium is collected from the cells and transported in crucibles to furnaces in the cast house. Each crucible holds about five tonnes of molten metal.
1.5t every 24 hrs
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Aluminium taking shape
Before being cast, stacked, weighed and strapped prior to shipment to our customers the metal is tipped into furnaces and cast into ingot, billet, rolling block or T-bar.
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Quality control all the way
Around 70% of the aluminium produced at Tiwai is cast as ingots using automatic casting machines. Billet, rolling block and T-bar are cast using a vertical direct chill casting process, producing products of up to 7 metres in length.
After casting, billet is ultrasonically tested and homogenised to ensure a uniform crystalline structure throughout.
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Transporting the final product
The majority of the aluminium is trucked to the Tiwai wharf and loaded onto a ship for export to Asia, the United States and Europe, with approximately 10% used in the domestic market.
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