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6.
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8. G. Akovali, C. A. Bernardo, J. Leidner, L. A. Utracki,
M. Xanthos, Eds., Frontiers in the Science and Technology
of Polymer Recycling, NATO Advanced Study Institute
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2012, p. B1.
10. J. Berry, Plastic #5 recycling got you feeling blue?,
http://earth911.com/news/2009/02/03/plastic-5recycling-got-you-feeling-blue.
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PERSPECTIVE
The Challenges of Reusing Mining
and Mineral-Processing Wastes
Zhengfu Bian,1* Xiexing Miao,2 Shaogang Lei,3 Shen-en Chen,4
Wenfeng Wang,5 Sue Struthers6
Mining and mineral-processing wastes are one of the world’s largest chronic waste concerns.
Their reuse should be included in future sustainable development plans, but the potential
impacts on a number of environmental processes are highly variable and must be thoroughly
assessed. The chemical composition and geotechnical properties of the source rock determine
which uses are most appropriate and whether reuse is economically feasible. If properly evaluated,
mining waste can be reused to reextract minerals, provide additional fuel for power plants,
supply construction materials, and repair surface and subsurface land structures altered by mining
activities themselves.
ining and mineral-processing wastes—
the solid and liquid materials generated after mining and ore processing at
or near mine sites (1)—have no current economic
use. A number of environmental problems are associated with the disposal of this waste, including contamination of streams and lakes (2) and
pronounced landscape transformation (e.g., stockpiled waste rock and tailings, subsidence basins,
open pits, and removal of overburden rock and
topsoil) (Fig. 1). Despite several efforts to reduce
the amount of waste produced, solid mineral wastes
remain one of the world’s largest waste streams
M
1
Institute for Land Resources, China University of Mining and
Technology, Xuzhou, Jiangsu Province 221116, China. 2State Key
Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology, Xuzhou, Jiangsu
Province 221116, China. 3Jiangsu Key Laboratory for Resources
and Environmental Information Engineering, China University
of Mining and Technology, Xuzhou, Jiangsu Province 221116,
China. 4Department of Civil & Environmental Engineering, University of North Carolina, Charlotte, NC 28223, USA. 5School of
Resource and Earth Science, China University of Mining and
Technology, Xuzhou, Jiangsu Province 221116, China. 6Skapa
Mining Services Ltd., Hillbanks, Burray, Orkney KW17 2SX, UK.
*To whom correspondence should be addressed. E-mail:
[email protected]
702
(3). For example, North America produces more
than 10 times as much solid mine waste as municipal solid waste per capita (4). Because mineral production continues to be necessary for
economic development, the recycling and reuse
of mining and mineral-processing wastes are
important management strategies now and in the
future (5).
The origin of mining and mineral-processing
wastes is closely related to the formation of the
target resource or minerals. For example, many
coal deposits exist in subsided regions resulting
from mountain formation; hence, the overlays of
coal resources are generally not very thick and
consist of relatively inactive sedimentary rocks.
In 2010, worldwide total coal production was
about 7273.3 million tonnes (Mt), with an estimated waste of about 1454.7 Mt due to coal production (6). Of this waste, up to 100% (total waste
with no production of prospective minerals)
may be due to the mining or extraction method.
Wastes produced during coal preparation (removal of undesired materials from coal through coal
washing, crushing, screening, and dewatering)
may reach 10 to 30% of raw coal; most of these
wastes are in slurry form as a result of the washing
process. The final form of waste can be detrimen-
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SCIENCE
13. New polymer offers closed loop recycling to automotive
industry, Waste Management World, 12 April 2012,
www.waste-management-world.com/index/display/articledisplay/2121000211/articles/waste-management-world/
recycling/2012/04/New_Polymer_Offers_Closed_Loop_
Recycling_to_Automotive_Industry.html.
14. Buildingtalk.com, Axion investigates carpet recycling
options, 15 January 2010, http://www.buildingtalk.com/
building-industry-news-/sustainability-and-energyefficiency-/axion-investigates-carpet-recycling-options/
364095.article.
15. M. Xanthos, in Mixing and Compounding of Polymers,
I. Manas-Zloczower, Ed. (Carl Hanser Verlag, Munich,
ed. 2, 2009), chap. 20, pp. 757–766.
10.1126/science.1221806
tal to the feasibility of reuse and recycling because
it dictates the cost of further processing.
Mining and mineral-processing wastes consist of rocks, soils, oil sands, and loose sediments.
The mineralogical and chemical characterizations
of mining wastes are useful in forecasting geotechnical properties (particle size and structure,
plasticity, bulk density, dry density, shear strength)
of the waste and the leachability of potentially
harmful compounds. The mineralogical composition of the processing wastes can be heterogeneous because of the deposition of wastes from
the processing of different mine sources, yielding
a range of physical and chemical properties. For
example, the mineral composition of tailings from
metal and nonmetal mines in China is divided
into eight broad types (7).
The most important mineralogical considerations are those that influence mineral recovery,
decontamination, acid rock drainage, and processes that affect sediment strength and cohesion.
The concentrations of toxic elements and metalloids such as Cd, As, Hg, Cr, and Pb are highly
variable, but if present in sufficient quantities,
they may inhibit plant growth or degrade water
quality (8, 9). Methods such as mechanical separation, chemical carbonation, and hydrothermal
mineralization (10) can remove some of these
toxic elements, but may also in some cases mobilize metals in groundwater and surface waters
through oxidation.
The reuse of mining and mineral-processing
wastes may minimize the environmental impacts
related to disposal; however, some reuse and recycling measures may actually cause new and
serious environmental problems. The overall environmental costs can be determined by various approaches such as ecological risk assessment, life
cycle assessment, sustainability operations assessment, and ecological footprint estimates (3, 11, 12).
Economic cost-benefit analysis, however, is the
ultimate driver in terms of the feasibility of a specific reuse technology. If the costs of final target
material extraction or mine waste reuse method are
economically prohibitive, then even the most ecofriendly process methods will be difficult to implement without regulation or government subsidies.
www.sciencemag.org
Downloaded from www.sciencemag.org on August 22, 2012
2.
Applied Sciences, Vol. 351 (Kluwer Academic Publishers,
Dordrecht, Netherlands, 1998), chap. 1.
U.S. Environmental Protection Agency, Plastics,
http://www.epa.gov/osw/conserve/materials/plastics.htm.
PackagingLaw.com, US recycling rates for plastics bottles up
in 2010, www.packaginglaw.com/3232_.shtml.
A. L. Bisio, M. Xanthos, Eds., How to Manage Plastics
Waste: Technology and Market Opportunities
(Carl Hanser Verlag, Munich, New York, 1994),
chap. 10.
M. B. Priebe, Ecolife, www.ecolife.com/recycling/plastic/
how-to-recycle-pp-plastic-5.html.
S. Straus, Information on RM5 polymer bank note,
http://www.polymernotes.org.
M. Stones, Food-grade PP recycling moves closer, says
WRAP, www.foodproductiondaily.com/Packaging/Foodgrade-PP-recycling-moves-closer-says-WRAP.
SPECIALSECTION
www.sciencemag.org
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10 AUGUST 2012
Downloaded from www.sciencemag.org on August 22, 2012
One approach to minimize
cost is to improve waste processing efficiency, which depends on the optimization of
the resource allocation to minCrushing
imize environmental effects
Surface mining
Grinding
while maximizing the quantity
Overburden,
of wastes processed and the
open-pit stope
Ore separation
Tailings
associated benefits. Avoiding
Ore processing
waste in the first place is the
Waste water
Concentration
Waste rock
Land subsidence
dewatering
most favored means of increasing
waste processing efficiency beOre concentrate
for further processing
cause it has the least environmental impact and possibly
Rock fractures
Underground mining
involves the least energy spent
on waste disposal; however,
it is also the most difficult to
accomplish. The use of solid
Collapsed rock filling the mined area
mining waste as backfill and
stabilization material in underground coal mining is potentially a good way to increase Fig. 1. Waste generated and environmental effects during different mining stages.
efficiency, but the trade-off is
not straightforward because of
7. J. R. Zhang, W. Z. Wang, F. P. Li, A. D. Wang,
the energy costs related to additional tunnel op- practice in China but not in the United States.
Comprehensive Utilization and Resources of Metal Mine
erations to move the material, as well as the need Waste rock and tailings have also been used as
Tailings (Metallurgical Industry Press, Beijing, 2002).
to create open space for temporary waste stor- auxiliary source materials for producing build8. M. A. Armienta et al., Appl. Geochem. (2012).
ing materials such as cement, hollow bricks,
age and management (13).
9. G. Geise, E. LeGalley, M. S. Krekeler, Environ. Earth Sci.
Residual mining wastes after reuse or re- concrete, and glass (17, 19–21). Ground sub62, 185 (2011).
10. G. T. Goodman, M. J. Chadwick, Eds.,
source recovery are typically discarded at spe- sidence basins induced by mining have also
Environmental Management of Mineral Wastes
cific sites such as tailing ponds. If wastes are been filled with waste rock and covered with
(Sijthoff & Noordhoff, Alphen aan den Rijn, Netherlands,
not disposed of properly, wastewaters, especial- topsoil. The repaired land can then be reclaimed
1978).
ly from hydrocarbon wastes, can enter streams as farmland, grassland, or construction land (11).
11. Z. Bian, D. Jin, J. Dong, S. Mu, J. Mining Safety Eng. 24,
132 (2007).
and potable supply wells. The primary goal for The waste rock or tailings can also be crushed
12. A. Golev, G. D. Corder, Miner. Eng. 29, 58 (2012).
disposal of mining and mineral-processing wastes and mixed with fly ash and cement as backfill in
13. X. Miao, J. Zhang, G. Guo, Method and Technology of
should be to ensure that the waste remains phys- mined cavities, which has the potential to reduce
Fully-Mechanized Coal Mining with Solid Waste Filling
ically, geographically, chemically, and radio- surface subsidence and is a promising method for
(China Univ. of Mining and Technology Press, Xuzhou,
logically stable and inert, and if this is not large amounts of waste reuse (22).
China, 2010).
14. D. M. Franks, D. V. Boger, C. M. Côte, D. R. Mulligan,
possible, the wastes must be isolated and preIt is difficult to assign a universal method to
Resour. Policy 36, 114 (2011).
vented from interacting with the ecosystem reuse all kinds of mining and mineral-processing
15. M. L. Smith, R. E. Williams, Eng. Geol. 43, 11
(14). Reuse of discarded mine waste, referred wastes. Each kind of waste has its own appro(1996).
to as tailing recovery, helps reduce exposure priate ways for reuse, which even can vary
16. H. Liu, Z. Liu, Resour. Conserv. Recycling 54, 1331
of waste to the environment and in some cases according to local environmental conditions (e.g.,
(2010).
17. ASTM, Standard Specification for Steel Slag Aggregates
can maximize target mineral efficiency (15). proximity to drinking water, depth of mining acfor Bituminous Paving Mixtures, D 5106-08
For example, waste rock or coal slime gener- tivity). In any situation where mining and mineral(2008).
ated after washing processes may contain car- processing wastes are reintroduced back to the
18. K. M. Skarżyńska, Waste Manag. 15, 83 (1995).
bon with calorific values of 3350 to 6280 kJ/kg, subsurface, efforts must be made to ensure that
19. Y. Chen, Y. Zhang, T. Chen, Y. Zhao, S. Bao, Construct.
which can be remixed with coal for additional no pollutants transfer from mining wastes to
Build. Mater. 25, 2107 (2011).
20. M. Frías, M. I. Sanchez de Rojas, R. García,
power generation (16). As above, the reuse of food or water supplies. Appropriate environA. J. Valdés, C. Medina, Cement Concr. Compos. 34,
mine tailings or coal slimes also may have po- mental monitoring and assessment studies should
678 (2012).
tential negative environmental impacts, such as always be included in the reuse design.
21. J. J. M. Heynen, H. N. J. A. Bolk, G. J. Senden,
increased emissions of nitrogen dioxide and sulP. J. Tummers, in Waste Materials in Construction,
fur dioxide.
J. J. J. M. Goumans, H. A. van der Sloot,
T. G. Aalbers, Eds. (Elsevier, Amsterdam, 1994),
Considering the factors that dictate when
References and Notes
pp. 655–664.
and where mining waste reuse makes sense
1. K. A. Hudson-Edwards, H. E. Jamieson, B. G. Lottermoser,
22. X. Miao, J. Zhang, M. Feng, J. China Univ. Mining
environmentally, economically, or both, there
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Technol. 18, 479 (2008).
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Acknowledgments: Supported by Natural Scientific Fund of
ects. Waste rocks and iron/steel slags have
3. L. Tiruta-Barna, E. Benetto, Y. Perrodin, Resour. Conserv.
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111 Project grant B07028.
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6. “Statistical Review of World Energy 2011,” BP Report
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for roadways and parking areas is an accepted
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