Relevant text from the paper:
We see immediately that this reaction is different from Equa-
tion 1. Here, oxygen is formed at the anode, which environmentally
is a highly favorable gas, compared with CO2.
The dream would of course be to have anodes that lasted as
long as the cell life, which now may be up to 5 years or longer.
Anode changes would then not be necessary after the cell has been
started. Nevertheless, it is a chemical fact that all materials have a
ﬁnite solubility in the very corrosive cryolitic melts at about 960◦C,
so a totally inert anode will probably never be found for use in
these electrolytes. Thus, what we really are looking for is a slowly
consumable anode. But how slow a consumption rate can we tolerate?
The potential inert anode material must have low solubility
and low reactivity in the electrolyte and also show good chemical re-
sistance against the anodically produced hot oxygen gas. In addition,
the anode material should be physically stable at the operating tem-
perature, mechanically robust and resistant to thermal shock. There
will be extreme requirements for keeping the wear rates of these
anodes low. A wear rate of the order of 10 mm/y may perhaps be
sufﬁcient, but lower values would certainly be beneﬁcial.
There are two main challenges in the development of inert
anode materials. In addition to the requirement that the anode ma-
terial should survive sufﬁciently long in the electrolyte, the metal
produced must be of adequate purity. The impurity metal content in
the aluminum can indeed be very signiﬁcant for the customers, and
the need for making pure aluminum will become more stringent in
coming years. The corrosion products, caused by the dissolution of
the anode material into the electrolyte, predominantly will end up in
the metal phase and thereby contaminate the aluminum produced.
Hence, the anode corrosion should be low enough to give impu-
rity contents corresponding to the present speciﬁcations for smelter
grade aluminum.
There are three principal potential advantages in favor of de-
veloping a new cell technology with inert anodes:
1. Cost reduction. All costs directly associated with the consumable
carbon anode will then be eliminated, including the capital saving
and raw materials costs by eliminating the need for the carbon
anode fabrication, baking, and also the anode rodding plant. These
cost savings may be signiﬁcant. It has been indicated that there
might be 25% to 30% lower capital costs for a new potline with
inert anode cell technology.3
2. Environmental friendliness. Inert anodes would eliminate all
greenhouse gas generation and emissions from the electrolysis
cells. Smelters would no longer generate CO2, carbon monoxide,
or perﬂuorocarbon gases (CF4and C2F6), because carbon would
no longer be used as anode material. Carbon residues (butts) will
of course disappear. In addition, the ﬂuoride and dust emissions
during anode change will also be eliminated.
3. Improved occupational health issues. Inert anodes would reduce
the work practices associated with the present prebaked carbon
anode change. The frequency of anode changes will certainly be
drastically reduced with inert anodes. Working conditions in the
potrooms would also be improved by avoiding all anode effects.
The outlook of the primary aluminum industry may be sum-
marized as follows: This is now a mature industry, which presently
(2013) suffers severely from low aluminum prices and a very chal-
lenging market situation.
Technologically, the present aluminum production process can
be a close-to-zero greenhouse gas producer. The ﬁrst step, which is
actually ongoing, is to focus on lower speciﬁc energy consumption,
and also to eliminate the occurrence of anode effects. Furthermore,
it is possible to reduce the inherent production of CO2by reducing
the net carbon anode consumption, although this reduction can only
be perhaps 10% or even less with the existing carbon anode tech-
nology. Here, an inert anode, if such a material can be found and
developed for use in industrial aluminum production, would repre-
sent a remarkable technological breakthrough, because then oxygen
is formed at the anodes instead of CO2