corbis
COPPER MINES Above FPO
and Below the Ground Estimating the stocks of materials in ore, products, and disposal sites opens up new ways to recycle and reuse valuable resources. A MIT K A PUR T. E. GR A EDEL Yale Univ ersit y
F
or years, resource geologists have estimated the amount of minerals and other deposits suitable for exploitation. On the local level, these projections provide information for investment decisions by mining companies and for land use and
industrial development planning by governments and communities. On the global level, estimates of resource reserves combined with data on rates of use provide perspective on long-term sustainability. © 2006 American Chemical Society
may 15, 2006 / Environmental Science & Technology n 3135
The stocks of mineral resources are extracted and mobilized from the Earth’s crust and transformed into engineered commodities and goods at the desired level of quality. These goods and commodities reside in the economy as an in-use stock of resources as long as their performance does not fall below acceptable levels. A net buildup of in-use stocks usually occurs that depends on the varying lifetimes of the goods and commodities. In our technological society, the lifetimes of goods are getting shorter and, simultaneously, our rate of use of resources is increasing exponentially. This results in faster turnover of the stock of resources across its life cycle. At the end of their useful service lives, the goods and commodities exit the economy as discards headed either to waste repositories or to remanufacture and reuse. At each life-cycle stage of the resource—production, fabrication, manufacturing, use, and end-of-life—different types of stocks exist. This feature presents a classification of stocks and the methodology to assess them. The information on different types of stocks is useful for analyzing the economic and environmental implications of resource use and has relevance for various stakeholders (1). The quantities, or stocks, of resources in the ground are not a sufficient guide to the future, because other stocks also need to be considered. A recent paper by Elshkaki et al. showed that flows of lead from stock in use in The Netherlands will soon exceed the amount needed for lead-containing products entering use (2). Therefore, in principle, The Netherlands’s dependence on lead from mines could be replaced with metal reclaimed from discards. In another seminal study, Allen and Beh manesh showed that for many elements, the industrial waste streams being disposed of were richer in concentration than typical virgin ore bodies (3). In each case, this suggests that the concept of resource stocks must be considered much more broadly.
A typology of stocks The term “stocks” is inadequate because any mineral resource has several different stocks and various flows among the reservoirs that contain it. To make this point clearer, the diagram in Figure 1 shows several lithospheric and anthropospheric stock components, which are discussed next. The first principal component is geochemical stock, the amount of that mineral resource existing now in nature; that is, the total amount originally provided by nature minus that already removed by human action. In most cases, human action has made only slight perturbations to geochemical total stocks, although removal of the richer stocks has in many cases been extensive. Geochemical stock consists of two components, ore stock and distributed stock. Ore stock is the amount of a mineral resource that exists in concentrated form in deposits termed ores. Resource geologists estimate ore stock. When an estimate shows that deposits are rich enough to be mined at a profit, it is termed the reserve. When deposits are known to exist but consist of an ore 3136 n Environmental Science & Technology / may 15, 2006
grade that is too low to be currently profitable, that stock plus the reserve is termed the reserve base (4, 5). The ore stock and the reserve base are synonymous. The ore stock is the reservoir tapped by the mining industry. FIGURE 1
Types of stock and flows among reservoirs in the lithosphere and anthroposphere The sizes of the reservoirs on the diagram are meant to give a rough visual representation of the relative reservoirs’ contents for a typical resource. They are not drawn to scale and do not represent any particular resource or geographical location.
Ore
Distributed
In-use Deposited
Geochemical
Hibernating
Dissipated
Employed
Expended
The distributed stock is the amount of a geochemical resource that exists in nature in a distributed state, such as the very low concentrations of metal ions trapped in granitic or siliceous rocks. This stock is very much larger than the ore stock. Skinner estimates that the fraction of an element in mineral form is 0.01–0.001% of the total geochemical stock (6). Although the amounts of distributed stock are large, almost all of this material is so widely dispersed and the cost of acquiring it is so high that recovery and use appear to be totally impractical (7, 8). The quantity of distributed stock can be roughly estimated by multiplying the ore stock by 104 –105. The second principal component is employed stock, the amount of that resource present in the “technosphere”; it is the amount taken from nature for human use and not yet discarded. Small amounts of this resource may exist in stockpiles of various types, such as governmental strategic reserves, refinery stocks, and scrap holdings. The vast majority, however, is present in products of various types and ages: automobiles, buildings, computers, and so on. Employed stock consists of two components. Inuse stock is the amount of a resource that is in active use—the material we rely upon to perform appropriately in our everyday lives. Hibernating stock is the amount of a resource that has previously been consumed for a technological purpose, is not now being used, and has not yet been discarded. Examples of hibernating stocks include lead sheathing on telephone cables still in place but no longer connected
to the network and copper in obsolete computers stored on closet shelves. Quantifying hibernating stocks empirically is difficult because their quantity depends primarily on consumer behavioral patterns. The owner decides whether to discard or retain a product on the basis of convenience, how easily it can be properly discarded, its present economic value, and its possible secondary uses in the future. Few studies have quantified hibernating stocks. One study, conducted by Chan, investigated hibernating copper in 3 large corporations and 32 private residences in the state of Connecticut (9). The amount of hibernating copper in large corporations was very small because of cost and storage-space constraints. In private residences, the most common hibernating products that contain copper were cell phones, followed by televisions, videocassette recorders, desktop computers, and office electronics. The highest mass concentration of hibernating copper was in unused but retained refrigerators, followed by desktop computers, portable air conditioners, televisions, washers, and dryers. The ratio of in-use copper to hibernating copper was ~13:1. On average, each household had 1.1 kg of hibernating copper. The third principal component is expended stock, the amount of that resource that has been used for human purposes and then discarded or that has been lost from the technosphere by corrosion or wear during use. Expended stock consists of two components: deposited stock and dissipated stock. Deposited stock is the amount of a resource that has been deposited in landfills, mining containment ponds, and so on and that still resides in those places. If deposited stock is never recovered and reused, society has forfeited its value and its embedded energy. Because the locations of this material are known, the stock can be regarded as existing in “technospheric mines”. If the “ore” in technospheric mines is rich enough compared with that in geochemical ores, it may someday be viable to mine these deposits, just as ore bodies are mined today. Dissipated stock is the amount of a resource that has been used in the technosphere but has then been returned to nature in a form that makes recovery difficult or impossible. Examples include zinc in brass powder worn away from brake linings, copper in runoff from corroding roofs, cadmium from airborne incineration residues, and silver ions from photographic processing discarded into municipal wastewater. Metal is discarded (and sometimes measured) in seven distinct flow streams: municipal solid waste (MSW), construction and demolition debris, hazardous waste, industrial waste, end-of-life vehicles, waste from electric and electronic equipment, and sewage and sewage sludge. In general, each of these flow streams, except the last, is deposited in some kind of reservoir—municipal landfills, construction and demolition landfills, industrial landfills, and so on. If MSW is incinerated, the ash, which often contains high concentrations of metals, is similarly deposited.
Bertram et al. conducted an assessment of the copper in these seven discard streams in Europe (10), and Graedel et al. did the same on a global basis (11). In each case, the amount of copper in sewage and sewage sludge—a reasonable proxy for the amount dissipated—was only 0.3% of that in overall discards. Thus, >99% of discarded copper is potentially available for recovery and reuse.
Quantifying employed stock A technique for determining employed stock that, in principle, can approach any accuracy desired is static (“bottom-up”) quantification. In this method, the principal reservoirs that contain the material under study—buildings, automobiles, and so on—within a given geographical area are identified and counted. The quantity of the chosen material contained in each reservoir is determined, and the product of the number of reservoirs and the material contents of the reservoir provides the in-use stock value. In practice, such an approach requires large amounts of time and effort to be reasonably complete, and researchers may not have access to significant pieces of the needed information (e.g., the number of military aircraft and their material composition). Reasonable approximations are nonetheless of value. Static quantification has been greatly aided by the availability of geographic information system (GIS) databases, which provide substantial information on the location and abundance of reservoirs, such as buildings and power distribution systems, over a wide range of spatial levels.
A recent paper showed that flows of lead from stock in use in The Netherlands will soon exceed the amount needed for lead-containing products entering use. In the dynamic (“top-down”) approach to quantifying employed stock, the rate of input of a chosen material into a defined geographical area is first established. The material is then allocated across the spectrum of principal uses. For each use, an average in-service life is estimated. With this information, the rate at which material is discarded can be computed. The difference between the total inputs and the total discards over time produces a historical record of employed stock. Both the static and dynamic approaches are conceptually straightforward, but each faces challenges in implementation. For the static approach, a reasonably complete set of countable in-service reservoirs must be specified for the chosen material; buildings as copper reservoirs and automobiles may 15, 2006 / Environmental Science & Technology n 3137
FIGURE 2
Quantitative distribution of in-use copper stock in selected poor, middle-income, and wealthy regions of Cape Town, South Africa The bars indicate the quantities in six reservoirs within each region.
125,000
Poor community areas
Wealthy areas
75,000
Industrial/commercial areas 221,097
Building and construction Industrial machinery Infrastructure Transport Electronic and electric products Consumer and general products
100,000 In-use copper stock (kg/km2)
Middle-class areas
605,487
50,000
25,000
0 Gugulethu
KhayelitshaSite C
Gardens
Kenilworth Selected areas
as zinc reservoirs are common examples. Second, the typical contents of the chosen material in each of the reservoirs, or perhaps a mean and standard deviation for the contents, must be established. Finally, a protocol for counting each of the reservoirs must be developed. The dynamic method requires information not on final reservoirs, such as houses, but on the products within them that contain the chosen material, such as plumbing pipes or refrigerators. For each of these products, a statistical distribution of in-service lifetimes must be established. Data are then needed on historical imports or extractions of virgin resources or ore, metal, and metal-containing products into the chosen geographical area. In each case, the material content, or a statistical distribution thereof, must be determined. Generally, at least some of the information needed for either approach is difficult to obtain with reasonable accuracy. In this regard, typical reservoir contents of a material and the average lifetimes of long-lived products are hard to determine. The best approach scientifically is to use both the static and dynamic methods to conduct the assessment and then compare the results. The difficulty here is that much of the data, such as product import and export, tends to be available only at the country level, but accurate reservoir counting works best at urban or even household spatial levels. Perhaps a useful comparison could best be made in very small countries, such as Luxembourg or Singapore. 3138 n Environmental Science & Technology / may 15, 2006
Camps Bay
Constantia
Paarden Eiland
Epping Industria
Case studies of copper stock determination Our initial example of a determination of stocks is for employed copper stocks in Cape Town, South Africa. In this static quantification study, described in detail by van Beers and Graedel, six reservoirs were selected for evaluation: buildings of different types and construction, electricity distribution and telecommunications infrastructure, electric and electron-
Much of the data tends to be available only at the country level, but accurate reservoir counting works best at urban or even household spatial levels. ic products, industrial machinery and equipment, transport (e.g., vehicles), and consumer products (12). Typical copper contents were established for each. The result was a total in-use stock of 110 Gg copper; ~29% was contained in infrastructure, and the remainder was divided roughly equally among the other 5 reservoirs. We applied the ratio of in-use to hibernating stock established above to estimate hibernating copper stock in Cape Town at 8 Gg.
Kapur predicts that under different scenarios of future copper use and discards, the expended stock is expected to be 2–3× the employed stock (16). The loss of copper discards is expected to be greatest from the electric and electronics sector, followed by building and construction, infrastructure, and transport. FIGURE 3
Spatial density of in-use copper stock in Australia N
In-use copper stock (kg/km2) 0–1000 1001–2500 2501–5000 5001–10,000 >10,000
500
0
500 km
What does it all mean? These examples demonstrate that the static and dynamic approaches produce different types of results. Both generate estimates of in-use and hibernating stocks, but only the dynamic approach generates additional predictions of expended stocks. Ore stocks are evaluated by resource geologists, and distributed stocks can be roughly approximated from the magnitudes of the ore stocks. FIGURE 4
Copper stock reservoir diagram for North America and Planet Earth Details are discussed in the text. 1000
North America Global
800 Stock value (Tg)
In addition to the city-level determination, the availability of GIS data on the location of the reservoirs permitted the stock in selected regions of the city to be compared. As seen in Figure 2, the result was that poor areas were often characterized by higher spatial densities of in-use copper than were middle-class or wealthy areas. This unexpected result was a consequence of very high densities of housing in the poor areas, the presence of wiring and plumbing in most houses, and the ownership of a few items of consumer electronics and perhaps a motor scooter or old automobile. A second stock determination example, also performed by the static quantification method, focuses on Australia (13). This study, described in detail by van Beers and Graedel, used the same methodology and in-use reservoirs as for Cape Town; however, the typical copper contents of the reservoirs were different and reflected the different stages of technological development of Cape Town and Australia. The largest portion of in-use stock in Cape Town was in infrastructure, whereas Australia’s largest portion, 44%, was in buildings. Infrastructure copper amounted to 26% of the total. The remaining 30% was divided among the other 4 reservoirs. The analysis gives a total in-use copper stock of ~5 Tg, and we estimate 0.4 Tg as the hibernating stock. The spatial distribution of Australia’s in-use copper stock is shown in Figure 3. It obviously corresponds with the population centers of the country, located primarily in the south and east. Such urban areas are clearly where recycling and reuse activities should be located, rather than more generally spaced throughout the country. The quantification provides a business case for recovering and recycling this copper as it is discarded in the future. The previous examples are static snapshots of employed stocks. A dynamic quantification, however, permits both employed and expended stocks to be estimated. Such a study for copper stocks on the North American continent is described in detail by Spatari et al. (14). They used information on the flows of copper in the 20th century, together with the specification of lifetime distribution for copper products—plumbing, wiring, built-in appliances, electric and electronic equipment, infrastructure, motor vehicles, and other transport—to establish employed and expended copper stocks. The methods previously outlined can be used to subdivide these stocks as in-use (65 Tg), hibernating (5 Tg), deposited (85 Tg), and dissipated (0.2 Tg). Zeltner et al. performed a comparable analysis for the U.S., with similar results for stock in use (15). The dynamic stock determination method used for North America has been applied at the global scale as well. This analysis determined that the total in-use global stock of copper is ~330 Tg (16). Wittmer obtained a similar result (17). The amount of copper in waste repositories or lost to the environment is ~400 Tg, or a ratio of in-use to discards of nearly 1:1. We estimate the hibernating and dissipated stocks to be 24 and 1 Tg, respectively. A comparison of copper stocks at the global level and in North America is shown in Figure 4.
600 400 200 0
Ore
In-use Hibernating Deposited Copper stock type
may 15, 2006 / Environmental Science & Technology n 3139
TA B L E 1
Copper stocks at several spatial levels Geographical area
Geochemical
Employed
Expended
Ore Distributed In-use Hibernating Deposited Dissipated
Cape Town (Gg) — Sweden (Tg) 2.5 Australia (Tg) 43 North America (Tg) 130 Planet Earth (Tg) 940
— — 4.3 × 10 4 1.3 × 10 5 9.4 × 10 6 – 9.4 × 10 7
110 1.2 4.9 65 330
8 0.1 0.4 5 24
— 1 — 84.8 393
— — — 0.2 1
Year
Refs.
2000 1995 2000 1994 2000
12 19, 20 13 14, 18 16, 18
In Table 1, we collect results from the four examples along with similar values for Sweden (19, 20). A few general statements can be made on the basis of this table. First, the amount of copper in hibernating stocks, while admittedly only very roughly estimated, appears small, even though it is relatively easy to acquire. In contrast, the copper in deposited stock is a substantial fraction of, or roughly comparable to, the copper in in-use stock. However, reacquiring this copper is difficult, partly because it is usually deposited without reuse being considered. The amount of copper in dissipated stock is quite small, although its chemical form may make it environmentally significant. As the four examples in this paper and the results of Elshkaki et al. (2) demonstrate, the approximation of the magnitudes of various kinds of stocks is a tractable project. Stock estimation nonetheless demands considerable diligence in tracking down unpublished information or in determining values for which data have never been measured. As a consequence, the resulting values are unlikely to be highly accurate but are still of substantial utility to those in such areas as resource management, recycling strategies, and policy planning.
From the standpoint of material reuse, hibernating stocks present an interesting opportunity. Our estimates suggest that the quantities are not very large compared with rates of material entering use. Nonetheless, they are readily accessible for the most part and are not of significant perceived value to the owners. Thus, these stocks could quickly enter the recycling stream if owners are given modest incentives. In contrast, material in use may be unavailable for recycling for decades, and that in deposited or dissipated stocks may be prohibitively expensive to locate, mine, and process.
The information on
It is clear that establishing data on stocks of used materials is feasible and valuable. Just as clear, however, is that the data are often problematic and that the methodological approaches are at early stages of development. We hope that this paper will spur increased efforts to better characterize and use stocks of materials, especially those with low relative abundance and distinct physical and chemical properties that have won them the label “nutrients of technology”.
future discards can provide insights on the design of the next generation of products for better recovery, reuse, and recycling. An awkward feature of stock determination is that it is easiest to accomplish for very large spatial levels (e.g., countries and larger), because that is where the most apposite data are collected. Stock determination is most useful, however, on very small spatial levels (e.g., urban and smaller), where the necessary data are often sparse. Improved techniques to scale results from one spatial level to those smaller or larger will be very valuable. 3140 n Environmental Science & Technology / may 15, 2006
As the quality of life in terms of basic infrastructure and provision of services in developing economies approaches that of industrialized nations, the ratio of lithospheric stock to anthropospheric stock will decline rapidly, and this could lead to concerns over scarcity (21). Although economists have long debated the scarcity of resources, it is important to point out that the methodology presented in this paper can be used to make projections of future discards from the in-use stock of materials. The information on future discards can provide insights on the design of the next generation of products for better recovery, reuse, and recycling.
Amit Kapur is now a postdoctoral fellow in the School of Natural Resources and Environment at the University of Michigan. T. E. Graedel is a professor with the Center for Industrial Ecology, Yale University. Address correspondence to Graedel at Yale University, 205 Prospect St., New Haven, CT 06511 (thomas.graedel@yale.edu).
Acknowledgments This work was supported by grant BES–9818788 of the U.S. National Science Foundation. A discussion with R. B. Gordon and R. J. Lifset stimulated this research. For research that contributed to this paper, we thank M. Bertram, D. van Beers, M. Chan, and S. Spatari.
References
(1) U.S. Geological Survey. Metal Stocks in Use in the United States; Fact Sheet 2005-3090, 2005; http://pubs.usgs. gov/fs/2005/3090. (2) Elshkaki, A.; et al. The Environmental and Economic Consequences of the Development of Lead Stocks in the Dutch Economic System. Resour. Conserv. Recy. 2004, 42, 133–154. (3) Allen, D. T.; Behmanesh, N. Wastes as Raw Materials. In The Greening of Industrial Ecosystems; Allenby, B. R., Richards, D. J., Eds.; National Academies Press: Washington, DC, 1994, pp 69–89. (4) McKelvey, V. E. Relation of Reserves of the Elements to Their Crustal Abundance. Am. J. Sci. 1960, 258A, 234– 241. (5) Long, K. R.; DeYoung, J. H., Jr.; Ludington, S. Significant Deposits of Gold, Silver, Copper, Lead, and Zinc in the United States. Econ. Geol. 2000, 95, 629–644. (6) Skinner, B. J. Exploring the Resource Base. Unpublished notes for a presentation to the Conference on Depletion and the Long-Run Availability of Mineral Commodities, Washington, DC, April 22, 2001; summarized in Ref. 7, pp 66–67. (7) Gordon, R. B.; et al. Toward a New Iron Age? Harvard University Press: Cambridge, MA, 1987. (8) Tilton, J. E. On Borrowed Time? Assessing the Threat of Mineral Depletions; Resources for the Future: Washington, DC, 2003. (9) Chan, M. Hibernating Copper in Connecticut Residences and Corporations. Master’s Thesis, School of Forestry and Environmental Studies, Yale University, New Haven, CT, 2004. (10) Bertram, M.; et al. The Contemporary European Copper Cycle: Waste Management Subsystem. Ecol. Econ. 2002, 42, 43–57.
(11) Graedel, T. E.; et al. The Multilevel Cycle of Anthropogenic Copper. Environ. Sci. Technol. 2004, 38, 1242– 1252. (12) van Beers, D. ; Graedel, T. E. The Magnitude and Spatial Distribution of In-Use Copper Stocks in Cape Town, South Africa. S. Afr. J. Sci. 2003, 99, 61–69. (13) van Beers, D. ; Graedel, T. E. Spatial Characterization of Multi-Level In-Use Copper and Zinc Stocks in Australia. J. Clean. Prod. 2006, in press. (14) Spatari, S.; et al. Twentieth Century Copper Flows in North America: A Dynamic Analysis. Ecol. Econ. 2004, 54, 37–51. (15) Zeltner, C.; et al. Sustainable Metal Management Exemplified by Copper in the USA. Region. Environ. Change 1999, 1, 31–46. (16) Kapur, A. The Future of the Red Metal—Discards, Energy, Water, Residues, and Depletion. Prog. Indust. Ecol. 2006, in press. (17) Wittmer, D.; Lichtensteiger, T.; Baccini, P. Copper Exploration for Urban Mining. Proceedings of Cobre 2003, Vol. 2; Institute of Mining, Metallurgy, and Petroleum: Montreal, 2003; pp 85–101. (18) U.S. Geological Survey, Mineral Commodity Summary for Copper, 2004; http://minerals.usgs.gov/minerals/ pubs/commodity/copper/coppemcs04.pdf. (19) Sörme, L.; Bergbäck, B.; Lohm, U. Century Perspective of Heavy Metal Use in Urban Areas. Water, Air, Soil Pollut. Focus 2001, 1, 197–211. (20) Landner, L.; Lindeström, L. Copper in Society and in the Environment; Swedish Environmental Research Group: Västerås, Sweden, 1999; pp 39, 70, 87. (21) Gordon, R. B.; Bertram, M.; Graedel, T. E. Metal Stocks and Sustainability. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 1209–1214.
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