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How Aluminium is Made
NEW ZEALAND ALUMINIUM SMELTERS LIMITED
The Process
NZAS uses the Hall-Heroult process to reduce An electric current, o approimately ,
amps
CARBON ANODE alumina to aluminium metal. The basic inputs are or ines , and ,
amps or ine ,
alumina, electricity and carbon. flows into the cells through carbon anodes which
orm the positive electrode and also supply the
OER In this process, alumina undergoes an electro- carbon or the reduction reaction. The current
METAL BAT
NTERACE 2Al O +3C 4Al + 3CO chemical reaction in individual reduction cells.
2 3 2 passing through the aluminabath solution reduces
These cells are long steel shells lined with the alumina to aluminium and oygen. The
reractory brics and carbon and are connected aluminium is deposited at the cathode, while the
ALMNM electrically in series. The carbon lining o the cell oygen is attracted to the carbon anode. The cells
orms the cathode. operate at temperatures o around
°.
Alumina Al is ed into the cells at regular
There are carbon anodes in ines , cells
intervals where it is dissolved in a bath o molten and
carbon anodes in ine cells. Aluminium
cryolite sodium aluminium fluoride . rods are attached to suspend them in the reduction
NZAS has our reduction lines ines , cells. The anodes, which are largely consumed
each containing
individual cells and ine in the reaction, are replaced by rota ater around
containing cells. days in the cell. sed anodes called butts, are
crushed and used in the production o new anodes
which are manuactured using petroleum coe,
The equation for the basic reaction is liuid pitch and the recycled carbon material.
2Al O +3C 4Al + 3CO
2 3 2
olten aluminium, which collects in the bottom
o the cell, is siphoned o and transported to the
cast house. ach cell in ine , produces Tonnes Tonnes Tonne
approimately ,
g o molten aluminium and Bauite Aluina Aluiniu
each cell in ine produces approimately ,
g 4 2
o molten aluminium every hours.
ases generated in the process are collected and
filtered through fluoride scrubbing euipment Metal Castin
beore being released to the atmosphere. olten aluminium is transported to the etal Two ingot casting machines, each capable o
roducts cast house in lined crucibles carried by casting up to . tonnes per hour, cast, stac,
Apart rom alumina, the primary reuirement in special purpose crucible transport vehicles. ach strap and weigh the ingots into one tonne bundles,
the smelting o aluminium is a constant availability crucible holds about five tonnes o molten metal. ready or transport.
o electricity at a competitive price. Around ,
h o electricity, two tonnes o alumina and The metal is tipped into the holding urnaces. illet, rolling bloc and T bar are cast using a
gs o carbon are reuired to produce one The holding urnaces are heated and hold vertical direct chill casting process producing up to
tonne o aluminium. the aluminium at
°, the desired casting seven metre lengths. illet can be cast in a variety
temperature. o diameters. Ater casting, billet is placed in a
homogenising urnace or reheating and cooling
Aluminium is cast as g ingot, rolling bloc under controlled conditions. This ensures a uniorm
and T bar lengths, or alloyed with other metals to crystalline structure throughout.
produce billet.
Raw Materials
auite is the ore rom which aluminium metal 4 The raw materials are mied and ormed into carbon The smelter’s main emission control euipment are
is acuired. auite is mined at eipa on ape or anodes weighing approimately , g or all ines. the ry Scrubbers, where dust particles and fluoride
eninsula in north ueensland. It is shipped to ¡io Tinto They are then baed at temperatures o up to ,
° or gases are removed rom cell emissions. There are dry
Alcan arwun and ueensland Alumina imited, in up to days. This baing process improves the strength scrubbers at NZAS which collect more than per cent
ladstone on the central ueensland coast or refining. and conductivity o the anode. itch volatiles are released o the fluoride gases rom process emissions.
2 and burnt to provide etra heat.
The fine white alumina powder Al is transported hemical reduction o alumina to aluminium taes
by ship to NZAS rom the alumina refineries. ¢our The carbon anodes are attached to aluminium rods place in individual reduction cells connected in an
tonnes o bauite produce two tonnes o alumina, which using molten cast iron to enable them to be suspended electrical circuit. The smelter has our reduction lines.
produces one tonne o aluminium. rom cell superstructures. They are then sprayed with ¡eduction ines , are housed in buildings
3 approimately g o molten aluminium to reduce metres long and all contain
reduction cells. ines ,
The electrical current reuired or the smelting airburn in the cell. They are distributed by an overhead are ¥aiser technology.
process flows in the reduction cell through carbon blocs conveyor to a distribution point where they are truced to
anodes to the cathodes in the bottom o the reduction the cells via an Anode Transport £ehicle AT£ . ¡eduction ine comprises more recent
cells. The anodes are made rom petroleum coe, liuid technology and is
metres in length, connected in an
pitch and recycled carbon anodes which are returned electric circuit. ine contains reduction cells.
rom the reduction process.
2 3 4
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