Environmental Engineering Reference
In-Depth Information
The most common measures applied to minimize ARD from waste dumps are:
●
Surface shaping and capping with low permeability material, to minimize ini ltration
of rainwater;
●
Total encapsulation to minimize ini ltration and also to restrict oxygen supply;
●
Preferential placement, with high capacity PAF materials placed in central parts of the
dump, and NAF materials in outer zones (Marszalek 1996);
●
Compaction to reduce overall permeability, to minimize cracks that enable ready
access to air and water, and to provide low permeability barriers.
These measures are facilitated where waste rock storages are formed by paddock dumping
and bottom-up construction methods (see Chapter Nineteen on waste rock disposal).
Commonly, the main constraint to management of ARD in waste rock storages, is the
availability of clay or other low permeability material for use in capping or encapsulation.
Impermeable membranes have been used; however, the costs would be prohibitive for
most operations. Another common constraint is that most of the oxidized wastes, suitable
for capping or placement of the outer zones of a dump, are produced in the initial stages
of mining while wastes produced in the i nal stages comprise mainly PAF material. This
constraint can be overcome, albeit at considerable cost, by stockpiling of oxidized wastes
for later use in capping.
One of the waste rock dumps at Mt Muro in Central Kalimantan, Indonesia, uses
a low permeability zone within the dump to impound water within the dump to main-
tain saturation of the PAF waste as shown in
Figure 17.8
. Another approach has been
to mix limestone with sulphidic waste rock so as to achieve neutralization
in situ
. (
Case
17.4
)
For tailings storage facilities with the potential for ARD, two alternative approaches
may be used. These are: (1) wet cover, which means maintaining a pond on the surface
of the tailings, thereby excluding atmospheric oxygen; and (2) dry cover, in which a low
permeability capping is placed over the surface of the tailings, limiting both the ingress of
oxygen and ini ltration of rainfall.
The design of covers and encapsulating layers depends on many considerations
including the properties of available materials, the physical and chemical characteristics
of the wastes, climatic conditions, and potential future land uses. Usually cover design
forms part of the overall dump design that also includes one or more layers for estab-
lishment of vegetation. Because of the differing, sometimes conl icting requirements, the
overall design may require cooperation between geochemist, mine planner, geotechnical
The main constraint to
management of ARD in waste
rock storages, is the availability
of clay or other low permeability
material for use in capping or
encapsulation.
FIGURE 17.8
Schematic Profi le through Mt Muro
Waste Rock Dump
Infiltration of
Rainfall
Surface
Run-on
Dump Crest
Water Table
within Dump
Dump
Outslope
Low
Permeability
Barrier
Potential
Acid-forming
Waste
Low Permeability
Substrate
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