Role of metals in sustainable development

7/28/2019 Role of metals in sustainable development

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The role of metals in sustainable development

T E Norgate and W J Rankin

CSIRO Minerals, Box 312, Clayton South, Vic. 3169 Australia

ABSTRACT

Metals are well suited to sustainable development goals. They are not biodegradable andhave virtually an unlimited lifespan and the potential for unlimited recyclability. Thusmetals can be considered as renewable materials. However mineral resources, the sourceof primary metals, are non-renewable as their supply is finite, but this does notnecessarily mean scarcity. In this paper the results from a series of Life Cycle

Assessments of primary metal production processes for copper, nickel, lead, zinc,aluminium and steel have been used to examine how metals may contribute to societystransition to sustainable development.Particular issues considered include:

current metal reserves and how these may change in the future,

some of the environmental impacts (Total Energy, Global Warming Potential andAcidification Potential) associated with primary metal production and how they will

be exacerbated by declining ore grades,

new processing technologies with lower energy consumptions and improved metalextraction efficiencies that will reduce reserve depletion and environmental impacts,

increasing the utilization of metals in use by recycling, with particular reference to

aluminium, the potential impact of a carbon tax on metal prices and how this may influence the

ways in which metals are used in the future.

INTRODUCTION

Resource consumption in the world is rising rapidly, driven by population growth andrising wealth. Projections suggest the global economy may grow fivefold in the nextthirty years to meet the aspirations of developing countries (World Resources Institute,2001) but there is real doubt as to whether the earth has the capacity to support

continuously escalating levels of resource extraction and disposal. Indeed the EcologicalFootprint method of analysis (Yencken and Wilkinson, 2000), which estimates the percapita material and energy requirements of populations of individual countries, indicatesthat the ecological footprint of the global population in 1997 was at least 30% larger thanthe Earths biological production capacity and it is projected that this may rise to 130%

by 2030.

These growing concerns with regard to escalating resource extraction and disposal havecontributed to the now widely accepted concept of sustainable development, which is


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broadly defined as development that meets the needs of the present withoutcompromising the ability of future generations to do the same. This concept recognisesthat economic growth must incorporate social and environmental objectives the so-called triple bottom line. It is generally considered that this will require greatly

improved efficiencies in the use of resources and also major reductions in wastegeneration and emissions in order to break the link between economic expansion andresource consumption.

One way of achieving greater efficiency in resource use is by dematerialisation, whichis broadly defined as the reduction in the amount of energy and materials required toservice economic functions (eg production of consumer goods or the provision ofservices). Some dramatic numbers have been reported in the literature in regard toestimates of necessary reductions in materials and energy intensities required to achievesustainable development.. For example, the Factor 10 proposal of Schmidt-Bleek(1996) suggests that in order to achieve any measure of sustainability, the economies of

industrialised countries need to deliver the same material outputs with a tenfold decreasein resource consumption. This represents a quantum leap in resource productivity and

points to a fundamental re-orientation of societys use of materials, and raises criticalquestions for resource extraction industries. Progress towards dematerialisation has beenmost successful in those countries which have a high GDP per capita while in countrieswith a relatively low GDP per capita the reverse trend has occurred (Petrie andRaimondo, 1997). Developing countries, where a large part of the new mineral wealth isconcentrated, are anticipated to follow the latter path. The hypothetical results presented

by Schmidt-Bleek (1996) suggest that this period of increased material and energyintensity in the developing countries might be as long as 50 years and that it may take inthe order of 100 years to achieve a Factor 10 dematerialisation on a global scale.

The closure of materials loops through the re-use of materials complements the processof dematerialisation. While smaller and lighter products with longer service lives canreduce the amount of materials required by society to operate the economy, re-use andrecycling can also minimise fresh inputs and waste outputs. Of the materials currentlyused by society, metals have the greatest potential for unlimited recycling. They are not

biodegradable and their elemental nature means they can have an unlimited lifespan.Thus metals can be considered as renewable materials. However resources of mineralsand metals are non-renewable, hence their supply is finite. But this does not necessarilymean scarcity, on the contrary, mineral reserves are now more abundant than at any timein the past (Stewart, 2001; Young, 2001).

The anticipated growth in the economies of the developing countries as they strive toimprove their standard of living means that there will be an on-going need for primarymetals for at least many decades, even with increased levels of dematerialisation andrecycling. Even the achievement of Factor 10 dematerialisation would still need amaintenance or make-up of primary metals, as thermodynamic constraints (ie a100% conversion efficiency is physically impossible) and metal quality and product


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recovery issues will limit the extent to which dematerialisation and metal recycling willbe possible.

Exploration, extraction and metal processing activities can contribute to sustainable

development goals by creating wealth and helping to alleviate poverty, particularly inremote and regional areas, as well as improving the health, education and standard ofliving of communities. In many countries the minerals and metals industry is a majorcontributor to that countrys well-being.

In this paper the results from a series of Life Cycle Assessments of primary metalproduction processes are used to examine how metals may contribute to societystransition to sustainable development. Issues such as metal reserves, future metalscarcity, metal recycling and carbon or energy taxes are considered.

METAL RESOURCES AND RESERVES

It is important to distinguish between resources and reserves. A resource is aconcentration of naturally occurring material in the earths crust in such form and amountthat extraction of a commodity from the concentration is currently or potentially feasible.A reserve is that part of an identified resource which could be economically extracted or

produced at the time of determination. For example, estimated world reserves ofaluminium and iron are given in Table 1 at 3,910 and 65,000 Mt respectively, while theworld resources of these metals are estimated at 11,000 and 230,000 Mt respectively(Dzioubinski and Chipman, 1999; US Bureau of Mines, 1995). In practice, metalreserves change constantly, reflecting changes in metal prices and relative currencyvalues. The world reserves of metals from existing resources could increase

significantly if metal prices increase and/or new processing technologies aredeveloped that lower the economically recoverable ore grade from a resource.Alternatively, metal reserves may also increase through new resources being identified.The current reserves of some metals estimated from various sources are shown in Table 1along with typical economic processing ore grades (Kirk Othmer, 1995). These reserves

Table 1. Economic grades, reserves, production rates and years of supply.Metal Economic ore

grade(%w/w)

Reserves(Mt of metal)

Production in2000

(Mt/y)1

Years ofsupply

2,3

Year ofreserve

estimation

Iron/steel 30 - 60 65,000 842 77 1995

Aluminium 27 - 29 3,910 24.2 162 1997Copper 0.5 - 2 320 14.8 22 1997

Lead 5 - 10 65 6.6 10 1997

Zinc 10 - 30 142 8.9 16 1995

Nickel 1.5 - 3 47 1.1 43 1995Notes: 1. Includes primary and secondary metal.

2. Assumes consumption rate closely balanced to total production rate.3. Assumes no recycling.


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are also expressed in terms of years of current production (assuming no metal recycling)in this table.

In addition to metal reserves, the largest and rapidly growing stocks of metals are metals

in use. These stocks represent a virtually permanent asset for society because metals arenot consumed during production and use in the same way as energy or degradablematerials. The best known example of this is gold, of which it is estimated that 80% of allgold ever produced is still in use. In principle, metals can be recycled indefinitely and

passed along from one generation to the next. However in practical terms, this is onlypossible for metals used in non-dissipative applications where the metal can beeconomically recovered. Figure 1 shows how the years of supply term in Table 1increases as the recycling rate increases for the various metals considered. This figure

pre-supposes that there will be no problem in meeting these demands for scrap metal forrecycling. However this will depend on the life-span of the various metals in particularapplications. Figure 1 asymptotes to infinity for all metals at a recycle rate of 100%.

0

100

200

300

400

500

600

700

800

900

0 20 40 60 80 100

Recycle rate (%)

Yearsofsupply

Aluminium

Iron/steel

Nickel

Copper

Zinc

Lead

Figure 1. The effect of recycle rate on the supply of metals.

It is therefore inappropriate to link or equate the non-renewability of metal resources withfuture metal scarcity. The challenge is to devise policies and actions that will help societyto optimize the efficient use of metal resources and stocks while at the same timeminimising their environmental impacts. This will include frameworks to provideguidance to manufacturers in their selection of materials and to consumers in their choiceof products that aim to be more environmentally friendly. One of the tools now beingused to this end is Life Cycle Assessment (LCA).

LIFE CYCLE ASSESSMENT OF METAL PRODUCTION PROCESSES

Life Cycle Assessment (LCA) is a technique for assessing the potential environmentalimpacts associated with a material or product from cradle to grave, that is, from raw


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material acquisition to the production, use and disposal of the material or product. Itinvolves the compilation of an inventory of relevant environmental exchanges of thematerial or product throughout its entire life cycle and evaluating the potentialenvironmental impacts associated with those exchanges. This life cycle approach to

process analysis had its origins in energy analysis studies in the 1960s and early 1970s(Weidema, 1997). The methodology has been progressively refined over the last twodecades and is now the subject of an international standard (ISO 14040 series). Theobjective of most LCA studies is to find the design option that minimises the life cycleimpact of the process or product. LCAs are increasingly being used by consumers ofmetal and other material products, regulators and environmental advocacy groups toevaluate environmental performance along todays increasingly complex supply chain. Adescription of LCA methodology is given in a previous paper (Norgate and Rankin,2000).

A series of LCAs on primary metal production processes for copper, nickel (Norgate and

Rankin, 2000), lead, zinc (Norgate and Rankin, 2002), aluminium (Norgate and Rankin,2001) and iron and steel (Norgate and Rankin, unpublished) have been carried out as partof CSIRO Minerals research commitment to sustainable resource processing. TheseLCAs were restricted to cradle-to-gate (ie from ore extraction through to the pointwhere refined metal is made available to the secondary manufacturing sector) and basedon process data derived from the literature. A number of alternative process routes (eg

pyrometallurgical and hydrometallurgical) were considered for each metal. While thereare a number of environmental impact categories that can be included in an LCA(Weidema, 1997), the impact categories considered in these studies were total (or full-cycle) energy consumption, Global Warming Potential (GWP) and AcidificationPotential (AP). The latter two categories are the combined contributions of the various

gaseous emissions to the environmental impacts of global warming and acid rainrespectively, and are expressed in terms of kg CO2-equivalent or kg SO2-equivalent perkg of metal produced (Norgate and Rankin, 2000). The key results of these LCAs aresummarised in Table 2 and shown in Figure 2 for black coal-based electricity. It should

be noted that in many instances there is no real choice as to which process should be usedin a particular situation this is largely determined by the nature of the deposit,

particularly the ore mineralogy and grade.

Newer or novel metal production processes and developing technologies for existingprocesses may lead to significant reductions in the energy and GWP values given inTable 2. For example, Norgate and Rankin (2001) have reported that technologiescurrently being developed for the the Bayer/Hall-Heroult processing route for aluminium

production, such as inert anodes, drained cathodes and low temperature electrolytes, maygive reductions in the order of 30% and 40% for total energy and GWP, respectively, forcoal-based electricity or 50% and 70%, respectively, for natural gas-based electricity.

The results in Table 2 are only for the cradle-to-gate stage of the metals life cycle.Subsequent downstream use of the metals have not been considered here. Inclusion of thelatter stage (ie gate-to-grave) will have a significant effect on the comparative


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Table 2. Life cycle energy, GWP and AP for various metal production processes.

Metal Process Total energy(MJ/kg)

GWP1(kg CO2 e/kg)

AP1(kg SO2 e/kg)

Iron/steel BF/BOF2

22 2.3 0.02Aluminium Electrolytic3 211 22.4 0.13

Copper Pyromet4Hydromet5

3364

3.36.2

0.040.05

Lead BF6ISF7

2032

2.13.2

0.020.02

Zinc Electrolytic8ISF

4836

4.63.3

0.060.03

Nickel Pyromet9Hydromet10

114194

11.416.1

0.130.07

Notes: 1. Black coal-based electricity

2. Blast Furnace & Basic Oxygen Furnace (iron ore, 64% Fe, 50% lump, 50% fines, open-cut mine)3. Bayer & Hall-Heroult processes (bauxite ore, 17.4% Al, open-cut mine)4. Matte smelting, converting & electro-refining (sulphide ore, 3.0% Cu, underground mine)5. Heap leaching, solvent extraction & electrowinning (sulphide ore, 2.0% Cu, underground mine)6. Blast Furnace (ore 5.5% Pb, underground mine)7. Imperial Smelting Furnace (ore 5.5% Pb, underground mine)8. Roasting & electrolysis (ore 8.6% Zn, underground mine)9. Flash furnace smelting & Sherritt-Gordon refining (sulphide ore, 2.3% Ni, underground mine)10. Pressure acid leaching, solvent extraction & electrowinning (laterite ore, 1.0% Ni, underground mine)

0

5

10

15

20

25

Alum

iniu

m

Copp

er

Copp

er

Iron/steel

Lead

Lead

Nick

el

Nick

elZi

ncZi

nc

GWP(kgCO2e/kgm

etal)

Pyro

Hydro

BFISF

Pyro

Hydro

ISFElect

Figure 2. Life cycle GWP for the production of common metals.

environmental impacts of some metals. For example, the use of light metals in transportapplications (such as vehicle manufacture) would significantly reduce life cycle energy


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consumption and greenhouse gas emissions associated with these applications (Martchekand Pullen, 1996; Das, 2000).

THE INFLUENCE OF ORE GRADE

The ranges of current economically recoverable ore grades for a number of metals weregiven in Table 1. As higher grade reserves are progressively depleted, the mined oregrades will gradually move down these ranges. For example, the average grade of copperore mined in the United States over the last century is shown in Figure 3 (Kirk Othmer,1995). This reduction in grade has a dramatic effect on the energy consumption andaccompanying greenhouse and acid rain gas emissions from metal production processes.This is illustrated in Figure 4 for copper production. A similar trend has been found fornickel production (Norgate and Rankin, 2000).

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

1900 1920 1940 1960 1980 2000

Year

Oregrade(%Cu)

Figure 3. Decline in average copper ore grade in the United States.

0

5

10

15

20

25

30

35

0 1 2 3 4

Ore grade (% Cu)

GWP(kgCO2equivalent/kg) Pyrometallurgical route (see Table 2)

Hydrometallurgical route (see Table 2)

Figure 4. Effect of ore grade on GWP for copper production.


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The impact of declining ore grade on GWP shown in Figure 4 comes about largelybecause of the additional energy that must be consumed in the mining and mineralprocessing stages to move and treat the additional gangue material. Once a concentrate ormineral product of a specified grade has been produced, the downstream processing (eg

smelting and refining) is not significantly affected by the original ore grade. The greaterthe contribution that the mining and mineral processing stages make to the overallprocess energy consumption, the greater will be the effect of ore grade. This point isillustrated in Figure 4 where the mining and mineral processing stages contribute 60%and 30% to the overall energy consumption for the pyrometallurgical andhydrometallurgical processes respectively, with ore grade having the greater impact onthe former process.

METAL RECYCLING

One way of reducing the rate of depletion of metal reserves is by recycling of metals-in-

use. It is widely recognised that recycling of metals results in significant savings inenergy consumption (and hence reductions in greenhouse gas emissions) when comparedto primary metal production. For example, the following energy savings have beenreported in the literature:

copper 84% (Bureau of International Recycling , 2001; Kellog, 1977)nickel 90% (Kellogg, 1977)aluminium 95% (Kvande, 1999; Altenpohl, 1998; Martchek, 2000)steel 60% (International Iron and Steel Institute, 2001)lead 65% (Bureau of International Recycling, 2001)zinc 75% (Martchek, 2000)

While the terms recycling rate and recovery rate are sometimes used interchangeably inthe literature, they usually refer to two different measures (recovery, or reclamation,

precedes recycling). The recovery rate is the proportion of scrap metal available at theend of its useful life that is actually recovered, while recycling rate is the proportion thatscrap metal contributes to the total consumption of that metal (both being expressed as

percentages). Thus while the recycling rate for some metals may be in the order of 40%,the recovery rates for those metals may be much higher. For example, Henstock (1996)reported that while the recycling rate for aluminium in the UK in 1988 was 31%, therecovery rate was 63%. Metal recovery rates are more difficult to calculate than recyclingrates as the total amount of scrap metal available is not always known. Current recyclingrates for common metals (taken from a variety of sources) are shown in Table 3 forAustralia, United States and the World.

Using aluminium as an example, Figures 5 and 6 show the effect of the number ofrecycles, assuming a closed-loop recycling system (ie material is returned to the original

process) on the total energy consumption and GWP respectively for secondaryaluminium production at various recycle rates. The basis of the calculations underlyingthese figures is given in Table 4 for the first five applications (ie four recycles) for the


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Table 3. Current recycling rates of various metals.Recycling rate (%)Metal

Australia United States World

Aluminium

CopperIron/steelLead

NickelZinc

22

36

32

456460

40

40

3847473436

0

50

100

150

200

250

0 5 10 15 20 25

Number of recycles

Totalenergy(MJ/kgaluminium)

20% Rec rate

40% Rec rate

60% Rec rate

80% Rec rate

100% Rec rate

Figure 5. Effect of number of recycles and recycling rate on total energy consumption

for secondary aluminium production

0

5

10

15

20

25

0 5 10 15 20 25

Number of recycles

GWP

(kgCO2-e/kgaluminium)

20% Rec rate

40% Rec rate

60% Rec rate

80% Rec rate

100% Rec rate

Figure 6. Effect of number of recycles and recycling rate on GWP for secondaryaluminium production.


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case of 100% recycle rate (ie the aluminium is continuously recycled with no furtheraddition of primary metal). For example, at recycle number 4, the total energy is equal to(211/5) + 9 = 51.2 MJ/kg, where the energy for primary metal production is 211 MJ/kg(Table 2) and the energy for recycling is assumed constant at 9 MJ/kg irrespective of the

recycle number (ie. 5% of the energy of the aluminium smelting step = 0.05 x 180 = 9MJ/kg). The latter value agrees closely with the value of 8.7 MJ/kg reported forsecondary aluminium production (Anon, 1997)). A similar result to that shown in Figure5 for total energy has also been reported by Kvande (1999).

The results in Table 4 illustrate how the environmental impacts associated with the initialprimary production of aluminium (in this case total energy and GWP) are progressivelydistributed over each recycle. At 20% recycle rate the corresponding calculation for totalenergy after four recycles becomes (0.8 x 211) + (0.2 x 51.2) = 179 MJ/kg, where thefirst term represents the primary aluminium component and the second term representsthe secondary aluminium component. In calculating the GWP for aluminium recycling

(0.55 kg CO2-e/kg Al) it has been assumed that the energy consumed in recycling (9MJ/kg Al) is mainly thermal (Kvande, 1999) and that natural gas is the fuel source. Thusthese two figures show how the average total energy consumption and associated GWP

per application, change over the useful life of the metal, with the average valuesobviously decreasing as the recycling rate increases.

Table 4. Total energy and GWP for secondary aluminium (100% recycle rate).PRIMARY ALUMINIUM RECYCLING SECONDARY

ALUMINIUMApplication

No.Recycle

No.

TotalenergyMJ/kg

GWPkg CO2e/kg

TotalenergyMJ/kg

GWPkg CO2e/kg

TotalenergyMJ/kg

GWPkg CO2e/kg

12345

01234

211 22.49.09.09.09.0

0.550.550.550.55

114.679.461.851.2

11.88.06.25.0

Metal quality and product recovery issues will affect the number of recycles possible inpractice. Recycling rates are very dependent on metal prices, and when metal prices drop,recycling rates drop. Recycling rate targets must take into account market growth andmetal durability (ie product life). The maximum amount of a material that can berecovered at any time is a function of the quantity put into service one average productlifetime earlier. The estimation of such a lifetime is by no means simple, eg Henstock

(1996) reported that the lifetime of copper ranges from 4 to 29 years with a weightedaverage of 17 years, while for zinc it ranges from 1 to 25 years with a weighted averageof 13 years. It is likely that advances in technology will help improve recyclingefficiency and economics.

Metal contamination during recycling by tramp elements is also an issue ofconsiderable importance. Tramp elements, such as copper in steel and iron and silicon inaluminium, are those elements that are more noble than the host metal and, hence, are


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very difficult (and expensive) to remove. Present strategies include better sorting ofmetals prior to remelting, diluting tramp elements by addition of primary metal and usingrecycled metal for lower grade applications (eg wrought products in the case ofaluminium). In the longer term, however, these strategies will need to be supplemented

by the development of effective refining processes for removing tramp elements. Whilethis will presumably increase the total energy consumption of secondary metalproduction, it could be expected to still compare very favourably with primary metalproduction. Metal recycling issues have been discussed in some detail by Wright et al(2002).

CARBON TAX

As a result of the 1997 Kyoto Protocol, governments around the world are increasinglylooking at introducing some form of energy or carbon tax as one way of reducing fossilfuel consumption and greenhouse gas emissions. The goal of a carbon tax is to enable the

price of goods and services to more truly reflect the social and environmental costsassociated with their production. Carbon taxes have already been introduced in a numberof industrialized countries, particularly in the European Union. Sweden has had a carbontax since 1991 and it currently stands at $US 44/t CO2 (Johansson, 2000) while Franceintroduced a carbon tax in 2001 at the rate of about $US 6/t CO2. An energy tax (ClimateChange Levy) was introduced in the United Kingdom in 2001. By assuming typicalcompositions and calorific values for the various fuel types, the carbon tax rate wasestimated by the authors to be in the range $US 5 - 11/t CO2. However the application ofthese taxes is often not straightforward. All European Union countries (with theexception of the United Kingdom) which have carbon or energy taxes have exemptionsfor energy-intensive users, and these exemption rates are often 80 100% of the full rate

(Arthur D Little, 1999).

The effect of a carbon tax in the range 0 50 $US/t CO2 (ie. 0 183 $US/t carbon) onprimary metal prices is shown in Figure 7 based on the LCA results in Table 2 for blackcoal-based electricity. This figure shows that a carbon tax would have the greatest effecton the price of aluminium, followed by steel, zinc, lead, copper and nickel in that order.These values depend on the magnitude of both the GWP emissions (see Table 2) and the

primary metal price. The primary metal prices used are shown in Figure 7.Some of the likely impacts of such a tax, in the absence of any form of exemption forhigh energy-intensive users, are to :

intensify efforts to develop more energy-efficient processes for metal production,particularly for energy-intensive metals such as aluminium,

change the way in which various metals are used, eg reduced use of energy-intensivemetals such as aluminium for construction purposes - aluminium mainly used wherelight weight is critical,

shift the balance of metal use to less primary metal and more secondary metal, iemore recycling of metals,


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focus attention on the use of renewable (ie non-fossil fuel) energy, eghydroelectricity, for the production of energy-intensive metals.

1.0

1.1

1.2

1.3

1.4

1.5

1.61.7

1.8

0 10 20 30 40 50 60

Carbon tax (US$/t CO2)

Relativepriceincreaseo

f

primarymetal

Aluminium ($US1500/t)

Steel ($US400/t)

Zinc ($US970/t)

Lead ($US480/t)

Copper ($US1635/t)

Nickel ($US6330/t)

Figure 7. Effect of a carbon tax on metal prices.METAL TOXICITY

While metals have been, and will remain, essential for the worlds technological progressand economic growth, their toxicological properties as well as their behaviour in theenvironment will influence the way in which metals will be used in the future. Toxicity isthe inherent potential or capacity of a substance to cause adverse effects on living

organisms that seriously damage its structure or function or results in death. The term isoften subdivided further into human toxicity (for humans) and eco-toxicity (for theenvironment). Published classification factors for metals (Heijungs, 1992) allow thesetwo environmental impact categories to be included in an LCA.

Some metals are essential for proper functioning of living organisms while others arenon-essential. Several non-essential metals are known to be toxic, even at very low levels(eg cadmium, lead, mercury and arsenic) whereas metals that are biologically essentialmay also become toxic at high levels, eg zinc and copper (Badilla-Ohlbaum, 1998). Theterm heavy metal appears to have arisen as a convenience among policy makers forreferring to metals with potential toxicity (Berdowski et al, 1998). For human

populations in general, exposure to metals occurs mainly through food and drink.

Plants are of particular concern because they may extract metals from polluted soils andmine wastes, making them available to animals, including stock, and humans who feedon the plants and animals. Thus plant uptake of metals has the potential for

biomagnification at higher levels in the food chain. However only a small fraction of themetals found in soils and in natural waters is bioavailable (ie capable of being taken up

by an organism). This is because the larger fraction is usually bound with reacting


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chemicals in the environment. Laboratory toxicity tests are conducted with artificialmedia by which all or most of the metal is made bioavailable and these tests thereforetend to overestimate the toxicity of metals in the environment. Recent research(Stubberfield, 2001) has highlighted this fact and recognised that it is the toxicity of the

bioavailable fraction that should be used to categorize and rank the hazard of metals andmetal compounds as part of an environmental risk assessment and also be used indrafting environmental regulations. Thus revised laboratory toxicity (ie leaching) testsare needed so that the true bioavailable metal concentration in a solid waste can be usedin conjunction with the metal classification factors mentioned earlier to allow metaltoxicity effects to be correctly incorporated into LCAs. Such approaches, along with newinformation, will help to revise our view of metal toxicity.

CONCLUSIONS

The unique properties that metals possess will see them play an important role in

societys transition to sustainable development. They will continue to contribute to theneeds of present and future generations in everyday applications and especially inemerging applications in a wide variety of areas such as electronics, telecommunicationsand aerospace. Despite earlier concerns about possible shortages of metals, there are noindications that metal scarcity will be a major problem for future generations. Howeverincreased energy consumption associated with decreasing ore grades and the likelyintroduction of carbon or energy taxes will see more emphasis placed on the use ofrecycled metals in the future and greater effort to re-design the supply chain of primarymetals to remove energy intensive steps. It is also likely that low energy-intensive metals(eg steel) will replace high energy-intensive metals (eg aluminium) in those applicationswhere any special properties of the latter (eg light weight) are not particularly critical.

Metal toxicological issues will also influence the way in which metals are used in thefuture.

Materials recycling will be a critical feature of sustainable development. Of all thematerials used by society, metals have the greatest potential for unlimted recycling - theelemental nature of metals means that they can virtually be reused and recycledindefinitely without loss of their properties. The ability to recycle metals offersopportunities to conserve resources, reduce energy usage and minimise waste disposal,all of which represent important contributions to sustainable development. However it isrecognized that there are practical and economic limits to the efficient collection,transportation and recovery of metals for recycling. Given that metal recycling rates tendto decrease when metal prices fall, it may be necessary to devise economic drivers thatencourage metal recycling when prices fall. Dematerialisation will complement materialsrecycling and will result in smaller and lighter products with longer service lives

produced with lower material and energy intensities.

The challenge that lies ahead is to devise policies and actions that will help society tooptimize the efficient use of metal resources and stocks while at the same time


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minimizing their environmental impacts. Environmental management tools such as LifeCycle Assessment will be increasingly used for these purposes.

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Role of metals in sustainable development