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Chemical criticality or rarity, meanwhile, relates to whether a metal is found
with others of similar chemical characteristics. The resulting cost of separation
can be expensive because of the fine chemistry and enormous quantities of energy
required. Recycling is then essentially undertaken to save energy and keep the metal
isolated from ones of a similar nature, throughout its entire life cycle.
The third category is that of absolute scarcity. Unsurprisingly, recycling here is
the most critical of all as a failure to do so will result in the irreversible dispersion
of a given element, leaving future generations to live practically without it. The
global objective, rather than energy quantities that can be saved, thus relates to
the need to conserve the element in the technosphere.
For all three, the entropic phenomenon of separation explained in Sec. 9.3 plays a
central role. To take an example, the element lithium may enter in the first scarcity
definition. This is because whilst there is a lot of lithium in the ocean, its extraction
is too costly. Scarcity pressures are then likely to be connected to the few land-
based concentrations such as the local salars of Bolivia, Argentina and Chile, or the
spodumene mines (those of lithium, aluminium and inosilicate). The rare earths,
meanwhile are affected by two of the scarcity criteria, in that they are not actually
geologically scarce but rather widely dispersed and always found together due to
their extremely similar chemical properties, which make their separation techni-
cally challenging and energy intensive. In such cases, supply depends primarily on
the new opening of mines, something which currently occurs almost exclusively in
China and secondly, on e
cient chemical separation and refining technologies. The
greatest criticality level is shown in the precious metals, for instance gold, which
apart from being found in dilute concentrations is geologically scarce.
Worth noting is the fact that although “entropic criticality” is comprehensively
examined by the authors, it is by no means the only way to examine the concept
of criticality. This is because it is also important to take into account the socioeco-
nomic, technological and environmental aspects of mining and metallurgy. Environ-
mental aspects could comprise, for example, ecological and water footprints. The
former can be effectively limited to the number of hectares of land, energy, time and
money required for the regeneration of the affected ecosystems affected. Equally
the water footprint can be reduced to the kJ needed to desalinate and transport
water from its natural location to where it is mass consumed.
That said, if one simply reduces the footprints to a number it would only impov-
erish the multidimensional message of mining's impact on society. For this reason,
the approach put forward by the authors centres on the thermodynamic aspects
i.e. on energy and entropy. It is however not exclusive and could incorporate
complementary forms of analysis.
14.3 Materials recycling: A global view
To really understand material recycling as a concept, a precise definition of what
is meant by it should be provided. Firstly, according to the International Resource
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