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is at each successive step, more di
cult to salvage. In other words, if no care
is taken, the recycling of one metal could prevent the recycling of others in the
recyclate. This effect is what the authors coined Entropic Backfire. Enhancing
physical separation processes prior to “waste metallurgy” notably reduces entropic
backfire. Even more does an adequately design of products that avoid complex and
heterogeneous mixtures of elements. The consequences of not doing this are obvious:
if society chooses to extract a desired material via the processes of material recovery
and recycling (either in the BoL from waste rock or in the EoL from recyclates),
society somewhat ironically could accelerate the evolution of final residues towards
Thanatia.
If by way of contrast, nothing is separated, then no further entropy is created.
The Second Law does not place limits on what is recyclable and what can ultimately
be recycled, this is instead left to what can be regarded as common (economic) sense.
Between the two extremes of complete or no separation, the optimum economic
point can be found whereby entropy is generated in both the reagents and the
waste recyclate.This is because as in all separation processes, there is an economic
threshold which hinders its “completion”.
14.8 Conventional vs urban mining
Minor metals are dominated by their entropic complexity given that their natural
concentration is low and that they are typically associated with a base metal that
constitutes the principal objective of mineral production.
As aforementioned, due to the disincentives associated with low grade mineral
extraction, minor metals often remain mixed in with waste rock or tailings, becom-
ing steadily diluted, compared to their unexcavated state in the mine. This dilution,
at the point closest to the y axis in Fig. 14.5, can be approximated to the concen-
trations present in Thanatia. At such concentrations a comparatively substantial
input of energy is needed for any beneficiation process. Furthermore, the condition
of the minor metal byproducts implies considerable energy consumption for their
metallurgical beneficiation, processing and refining from the base metal from which
they proceed.
In contrast to conventional mining, urban mining may be more complex as
previously explained. This depends on the final uses of the metal. Particularly, the
life of minor metals, except for the case of precious ones used in jewellery or coinage,
typically involves being alloyed, welded, chemically altered, mixed, doped or glued
with (or to) other non-metallic substances. This implies an entropic mixture with
other materials and their entropic dilution in the technosphere. A good example of
this is WEEE, the great majority of which has been dispersed, mixed and chemically
transformed into extremely di
cult to recover materials within an unbelievably
short period of time.
Reuter et al. (2005) provide an example of this through the cathode ray tube
(CRT), an electron gun contained in a vacuum tube, composed of Al and Cu,
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