Náttúrufræðingurinn - 1998, Page 69

llie calhode, and oxygen reacting with carbon
anodes which are dipped into the melt, thereby
forrning carbon dioxide which is then emitted.
The carbon anodes contain some sulphur leading
to emission of sulphur dioxide. A large amount
of electricity is necessary, both to keep the melt
liquid and to reduce the aluminium oxide to alu-
minium.
When the ISAL smelter was started in 1969
there where no hoods on the pots, but after the
pots were hooded and a modern technique of
transporting and charging the alumina to the
pots was introduced, it was possible to collect
the pot fumes in dry adsorption stations. Fluo-
rides and dust are removed from the gas by injec-
tion of alumina into the gas stream, whereby
fluorides and dust mix and react with the
alumina. The alumina is then recovered with bag
filters and finally used on the pots as secondary
alumina.
Perfluorocarbons, which are very stable non-
toxic but effective greenhouse gases, are emitted
during the so-called anode effect, which is a sud-
den voltage increase under the anodes if the
alumina concentration gets below a certain Iimit.
Through improved technique it has been possi-
ble to reduce the number of anode effects,
thereby reducing the emission of perfluoro-
carbons. Perfluorocarbons are not ozone-deplet-
ing.
PÓSTFANG HÖFUNDAR/AuTHORSADDRESS
Jón Hjaltalín Stefánsson
íslenska álfélagið hf.
Pósthólf 244/Box 244
IS-222 Hafnarfírði
Netfang/E-mail
jhs@isal.is
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