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Notes:

1 'Extraction' denotes refinery production for selenium, gallium, indium, cadmium and tellurium and mine production of others (see USGS 2000).

2 See Andersson (2000), Andersson and Râde (2001), Râde and Andersson (2001a) and Sternbeck (1998).

Notes:

1 'Extraction' denotes refinery production for selenium, gallium, indium, cadmium and tellurium and mine production of others (see USGS 2000).

2 See Andersson (2000), Andersson and Râde (2001), Râde and Andersson (2001a) and Sternbeck (1998).

By contrast, the rare metals have much lower crustal abundance and consequently require far greater geological enrichment to form minable deposits of separate minerals such as metal sulfides. In mined ores the rare metals are enriched from a hundred to some thousand times above their average concentrations in common rock. There is only a tiny fraction of the metal in the Earth's crust that is contained in such rich deposits (Skinner 1976). By far the major fraction of the total amount in the Earth's crust is contained in solid solutions in the silicate matrix of common rock, from which metal extraction would require immense energy inputs. Skinner (1987) has estimated the maximum land-based copper resources in mineral deposits to be in the range 1-10Pg. In fact, the known conventional resources of copper (the reserve base) plus the cumulative mine production already exceed 1Pg. Thus the end of new significant discoveries might not be very far away for copper and some of the other highly exploited rare metals.

Despite the fact that some new discoveries still are made, the sum of the reserves and the cumulative mine production of some metals, such as lead and nickel, has decreased over the last quarter of a century (Andersson and Rade 2001). Apparently, technological progress and new discoveries have not been able to compensate for increased costs due to (for example) environmental protection. In the years to come, technological progress will mitigate the escalation of recovery costs. Still, it might be overoptimistic to expect that the trends of cost reductions of the 20th century will continue in the 21st. Some have argued that implementation of environmental regulation worldwide and increased energy costs may increase recovery costs, and stronger forces working for the preservation of local environments may limit the access to land where ores are located (Hodges 1995). The preservation of land for tourism could, for example, prove more profitable than metal recovery. On the other hand, Tilton (1999) argues that real metal prices will not increase significantly over the next several decades, neither owing to ore depletion nor because of environmental regulation or land preservation. In our context we may note that, considering that the cost for nickel and lead already make up a relatively high share of the target cost for EV batteries (Table 31.1), the chance that EV manufactures could pay significantly higher prices for these metals appears to be limited.

Other metals that are mined (mostly) as main product or high-value co-product have reserve-to-extraction ratios that well exceed the 100 years envisioned as the time scale for the transformation of the energy system (Table 31.2). This is the case for platinum, lithium, rare earth elements and vanadium. For these metals annual availability may be a severer constraint than the available stock of resources. However, the mine production of these metals has grown by 2.5-5 per cent annually over the last three decades. Since they are main products, the mine production has the potential to grow at pace with the demand from an emerging technology. One obstacle may be that the mine production and the reserves are highly geographically concentrated: platinum and vanadium in South Africa, lithium in South America and rare earths in China. This increases the volatility of output and introduces uncertainty over the way economic development, monopolistic producer behavior, geopolitical relations and environmental considerations will affect the expansion of mine production.

The supply of metals that are mined as by-products will depend on the mine production of the main product. Tellurium and selenium are by-products of copper refining; indium, germanium and cadmium of zinc recovery, gallium of alumina production and ruthenium of the recovery of other platinum group metals. Gallium is about as abundant as copper and lead but seldom forms any mineral of its own (Figure 31.1). High enrichment is exceptional. This is also the case for the rarer element germanium and to some degree for selenium and indium. Tellurium and ruthenium exhibit higher enrichment factors but are less abundant. Cadmium is highly enriched in zinc ore but has a low economic value. Owing to the low grades in combination with relatively low prices, all these by-product metals typically generate less than 1 per cent of the revenues earned from the recovery of main products.

The by-product metals are not recovered from all mined ore where they are present and, where they are, recovery rates are often low. The recovery of cadmium can probably be improved only marginally, ruthenium by a factor of two and indium, tellurium and selenium possibly by a factor of two to six. The recovery of the more abundant metals, germanium and gallium, could possibly increase by up to two orders of magnitude. In addition recovery of metal by-flows mobilized by other large material flows, that is, waste mining (Ayres and Ayres 1996), could increase the annual availability. In the late 1990s, the germanium and gallium contents of combusted coals were about 500 times larger than the annual refinery production (Andersson 2000). As additional examples, cadmium could be recovered from phosphorous fertilizer, vanadium from petroleum refining and lithium from geothermal brines.

Table 31.3 By-product values in zinc ore

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