Geology Reference
In-Depth Information
renewable energy technologies, nine times the energy consumption of the entire globe
could be supplied. However, even when the capacity exists, such sources remain
barely exploited, with most of them (excluding hydropower) largely untapped: less
than 10% of geothermal and 5% of biomass, wind, tidal or solar energy potential is
being used. This questions the idea regarding the criticality of energy scarcity. Vast
amounts of energy are available on Earth so it seems that the depletion of fossil
fuels should not present a problem in the medium term. That said, alternative
energy technologies are manufactured with elements that are far from abundant.
Moreover, as the mines with the highest ore grades have been already exhausted, the
remaining ones need exponentially greater inputs of energy which in turn provoke
exponentially greater impacts on the environment. Therefore, in the challenge of
sustainable development one should account for all three aspects that come into
play: energy, materials and the environment.
17.3.2 Mineral endowment exergy replacement costs
Exergy has proved to be a fair indicator if one wants to make comparisons between
commodities. The value Man assigns to them is however very far removed from the
results obtained using exergy alone, especially when considering non-fuel minerals.
This explains why one needs to reassess the Earth's mineral endowment in terms
of exergy replacement costs.
For this endeavour, the authors calculated the exergy replacement costs of the
most important mineral commodities for which data was available. The “ingre-
dients” for such a calculation correspond to the average ore grades in Thanatia
and those in current mines together with the energy consumption associated with
the mining and beneficiation stages of mineral production. The minerals with the
highest exergy replacement costs, according to the authors' calculations, are gold,
tantalum, mercury, silver, cobalt, cadmium and tungsten. A mineral has a high
exergy replacement cost and is thermodynamically rare when 1) the concentration
of the mineral in the crepuscular crust is low and the difference between the ore
grade of the current mines and that in Thanatia is high and/or 2) when the energy
required to extract the mineral and beneficiate it is considerable (due to its physico-
chemical complexity).
When performing an evaluation of mineral endowment in terms of exergy re-
placement costs, one finds that it is around two orders of magnitude greater than
if calculated with exergy, which just goes to highlight how far human technology is
from reversibility. Specifically, the exergy replacement cost of the known non-fuel
mineral resources is over 8,000 Gtoe, whereas that of proved fossil fuels around 900
Gtoe. Aluminium, potash and iron constitute the greatest “exergy bonus” in the
crust, corresponding to 29.9%, 53.6% and 14.5% respectively of the total mineral
wealth. This exergy bonus relates to the considerably larger quantity of reserves for
the aforementioned minerals. An exergy cost analysis differs from a conventional
one in which resources are evaluated in mass terms. An example of this is, even if
 
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