The Exergy of the Earth and its Mineral Resources - Thanatia: The Destiny of the Earth's Mineral Resources - page 346

The exergy of the mineral reserves and world resources analysed is at least 1.75
and 14.3 Gtoe, respectively (1.9% and 16% of the total available fossil fuels in 2010
- 898 Gtoe). Such figures demonstrate that exergy as a property does not provide
a “fair” value to non-fuel mineral resources. Common sense would assign minerals
a physical value which is at least in the same order of magnitude as fuels. From
Man's perspective, the value of non-fuel minerals is often linked to their extraction
cost. A very abundant and concentrated mineral in the crust, such as iron, has
a high exergy value and a low exergy cost of extraction. On the contrary, a very
dispersed and scarce mineral such as gold, has a low exergy value but a very high
exergy cost of extraction.
This is why exergy replacement cost provides additional information for assign-
ing a physical value to non-fuel minerals. Exergy replacement cost is more closely
related to the market price than exergy alone (see Chap. 12). In fact, it could
be considered as a potentially fundamental ingredient of the final price of non-fuel
minerals.
11.3.3 The exergy of natural resources on Earth
In the previous sections the authors have expressed all mineral resources (both fuels
and non-fuels) with the same units, i.e. exergy. Such results will now be compared
with information on the remaining energy sources 14 provided in Chap. 6.
Table 11.20 summarises the exergy results of the resources that Nature provides,
those which could be potentially obtained using technology into the near future and
those which are used today. This information has been updated from Valero D. et al.
(2010b). All consumption values are correct as of the end of 2010, with the excep-
tion of those for biomass and non-conventional fossil fuels which are from 2005. The
information provided is divided into renewable (RW) and non-renewable resources
(Non-RW). For the group of renewables, the ratio between the current exergy con-
sumption and potential exergy use (RW use %) is given. For non-renewables, the
reserve to production ratio (R/P, yrs) is used as a measure of the depletion degree
of the considered mineral.
14 Note that the exergy of electricity is equivalent to its energy content. Hence, the energy figures
for geothermal, solar, wind, hydro and ocean power are equivalent to their exergy. The remaining
energy sources: nuclear and unconventional fuels were already expressed previously in Table 11.20
through their exergy content.