Mine Rehabilitation Handbook - Mining and Blasting

Where tailings are exposed, several options exist to stabilise the
exposed surfaces. These include:
• Cladding.
- Rock cladding or similar protective permanent armour to protect
against wind erosion on sites where plant growth and amelioration
of tailings is impractical. Rock cladding may, in some
circumstances, assist in the establishment of some vegetation.
• Capping.
- Isolating tailings by capping prior to revegetation, in order to
prevent the generation of toxic leachate that cannot be effectively
contained or recovered.
- Inhibiting infiltration so that leachate is not generated. This may
require reshaping the storage area to provide controlled drainage
away from the surface in the first instance. The tailings can then be
capped with a layer of compacted clay or similar impermeable
substance, over which a layer of free draining material is placed.
Topsoil is then used to re-surface the area prior to revegetation
(refer figure 6.3).
Figure 6.3
- Corrective measures to isolate tailings are likely to be very costly
and are a last resort measure. Prevention through proper design
and operation is cheaper and more effective.
• Amelioration & Vegetation.
- A self-sustaining vegetation cover is generally the most
satisfactory method for long-term stabilisation.
55
- Because of the inherent characteristics of most tailings, they will
require some change to their physical and/or chemical properties
in order to support satisfactory plant growth.
- Methods used to assist plant growth include:
a) Incorporation of Organic Materials and Mulches
e.g. sewage sludge, organic mulches, fly-ash etc
* Texture and structural characteristics are improved, aeration and
moisture infiltration and retention are increased.
* Micro-organisms are introduced to the growth medium.
* Organic materials tend to react with heavy metal ions and can
reduce toxicity.
* Woodchips, bark and similar materials when used fresh may
absorb available nitrogen and release phenols adversely
affecting plant growth. Where possible, stockpile prior to use.
* Fly-ash and similar material have been effectively used to
amend tailings material, but check levels of potential leachate
contaminants prior to use.
b) Correction of pH
* Acidic conditions are common; the oxidation of pyrite is most
frequently the source of acidity.
* Plant growth is very limited at pH 4.5 or less. Correction of pH
to 4.5 or above will substantially alter the availability of existing
or introduced plant nutrients (refer appendix 5).
* Various forms of lime are the most effective method of pH
correction. Lime demand may be excessive (in some cases 30
tonnes calcium carbonate equivalent (cce)/hectare). Correction
is generally impractical when required dosage rates exceed
about 15 tonnes cce/hectare.
* The acid-base status of the tailings material will determine the
lime demand, however, the following application rates can be
used as a guide for treating weak or moderately acid tailings (or
spoils etc):
pH Application Rate (tonnes/hectare
calcium carbonate equivalent)
6.0 - 5.5 2 - 5
5.4 - 4.6 6 - 9
4.5 - 4.0 10 - 13
56