Metal Stocks in Society – Scientific Synthesis - Unep Dtie

Metal Stocks in Society – Scientific Synthesis
Figure 3.
A schematic
diagram of the
methodology
for calculating
outflows from
in-use stocks.
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5. Outflows from In-Use Stocks
Outflows (if recycled) from in-use stock represent
a resource that decreases the requirements
for mining of virgin material (as well
as the associated environmental consequences).
Although the amount of outflow (the “secondary
material”) that is supplied to smelters
and refiners is generally measured, the outflow
itself is not, so must be computed.
The outflow computation requires dynamic
information on inflows over a number of
years, plus estimates of the fractions of that
flow entering each of the major uses, plus
estimates of the average lifetimes of those
uses, as shown in Figure 3.
It is important to mention that the potential
recyclability of the several individual outflows
can be quite different. For example, the recovery
efficiency of copper from infrastructure
is much more efficient than from electronics.
In the recycling report of this working
group (to be completed), these issues will
be addressed in some detail. In most uses,
some metal is lost to the environment by
processes such as dissipation or corrosion.
The amounts are quite small relative to other
flows, however (e. g., Wang et al., 2007; Mao
et al., 2008), and can be neglected for purposes
of assessing metal stocks in society.