Metal Stocks in Society – Scientific Synthesis - UNEP

Metal Stocks in Society – Scientific Synthesis5. Outflows from In-Use StocksFigure 3.A schematicdiagram of themethodologyfor calculatingoutflows fromin-use stocks.Outflows (if recycled) from in-use stock representa resource that decreases the requirementsfor mining of virgin material (as wellas the associated environmental consequences).Although the amount of outflow (the “secondarymaterial”) that is supplied to smeltersand refiners is generally measured, the outflowitself is not, so must be computed.The outflow computation requires dynamicinformation on inflows over a number ofyears, plus estimates of the fractions of thatflow entering each of the major uses, plusestimates of the average lifetimes of thoseuses, as shown in Figure 3.It is important to mention that the potentialrecyclability of the several individual outflowscan be quite different. For example, the recoveryefficiency of copper from infrastructureis much more efficient than from electronics.In the recycling report of this workinggroup (to be completed), these issues willbe addressed in some detail. In most uses,some metal is lost to the environment byprocesses such as dissipation or corrosion.The amounts are quite small relative to otherflows, however (e. g., Wang et al., 2007; Maoet al., 2008), and can be neglected for purposesof assessing metal stocks in society.22