The Range of Environmental Concerns - Mining and the Environment: From Ore to Metal - page 527

Other materials that are generated and/or used at mine sites may only occasionally or
periodically be managed as wastes (USEPA 1994). These include mine water removed
from underground workings or open pits, which usually is re-circulated for on-site
use (e.g. as mill or leaching makeup water) but at times is discharged to surface waters.
Leaching solutions are another example. They are typically regenerated and reused con-
tinuously for extended periods. On occasion, however, such as during temporary or per-
manent closure, the solutions may be disposed of, with or without treatment, as wastes via
land application or other means.
Finally, some materials are not considered to be wastes until a particular time in their
life-cycle. These include spent ore at heap or dump leaching operations: here, only when
active leaching for metal recovery ends is the spent ore that comprises the heap or dump
considered a waste.

Waste Rock

A number of environmental concerns are associated with the disposal of waste rock (see
Chapter Nineteen for a detailed discussion). Waste rock dumps have a large footprint, and
they often have a strong visual impact ( Figure 13.5 ). They represent engineering struc-
tures, and geotechnical stability cannot be taken for granted. Waste rock geochemistry
affects runoff and leachate, often turning water into wastewater. Finally, erosion by water
and wind may occur, and rehabilitation of waste dumps may be difi cult to achieve, espe-
cially in arid environments.
Waste rock removal and placement in open pit and open cast mining differ. From the
environmental viewpoint the notable difference is that in open cast mining, as in coal min-
ing in the eastern United States, the placement of overburden in mined-out areas min-
imizes or eliminates off-pit on-land overburden placement as illustrated in Figure 13.5 .
Thus reclamation can follow mining immediately. Another advantage is that the cut is
restricted to the area of the ore deposit, and unlike open pit mines, little adjacent waste
rock material is removed. However due to the large lateral extent of ore bodies typically
mined by open cast mining, the total Earth movement in open cast mining often rivals or
exceeds the Earth movement in open pit mining.

Waste rock removal and
placement in open pit and open
cast mining differ.

Tailings

After waste rock, tailings constitute the second major waste stream. Tailings consist of
i nely ground host rock from which valuable minerals have been removed. The host rock
has essentially no commercial value. Given their unique characteristics, safe and environ-
mentally acceptable disposal of tailings is far more challenging than the disposal of waste
rock. The materials are i ne-grained with high water content, the volumes are large, and
depending on the chemical composition of the ore, water discharging from tailings may
contain constituents which threaten the environment. Coal mining, on the other hand,
may produce no tailings, or may produce relatively small amounts of tailings from coal
washing operations, which remove reject materials such as stones and clay occurring
within or between the coal seams.
Many potentially severe environmental issues are related to tailings disposal. There is
the risk of failure of tailings containments, and the question of their long-term integrity.
Rehabilitation of tailings facilities and development of an economic land use after mining
are, in many situations, difi cult to achieve. Contaminated runoff and leachate from tailings
storage areas pose threats to groundwater and surface water quality. Tailings may be acid

Safe and environmentally
acceptable disposal of tailings is
far more challenging than the
disposal of waste rock.