Mine Rehabilitation Handbook - Mining and Blasting

Options for increasing the density of tailings include:
• mechanical thickening and filtering prior to discharge;
• multi-point discharges;
• discharge onto a sloping “beach” within the storage area to allow
drainage; and
• collection of liquor by under-drainage, decant structures or
filter walls.
Design of the tailings storage area and tailings discharge system to
provide for a permanent cover of water may be a viable alternative,
particularly in areas of high and reliable rainfall and where tailings have a
potential to be acid forming when oxidised. It is essential that the
tailings disposal option be designed to the specific site conditions.
Other important considerations in the disposal of tailings include:
• The location of storage areas to prevent or minimise external
catchment - this may require a location outside of valley sites or the
construction of permanent diversion structures.
• Ensuring geotechnical conditions are suitable or can be amended to
prevent undesirable seepage. Always seek professional advice.
• Where seepage of leachate has occurred, measures to recover
seepage and/or prevent infiltration and the formation of leachate will
be required. Recovery measures will need to continue to operate for
as long as seepage occurs.
• Constructing external slopes that will be stable and can be
revegetated or clad to resist erosion. Maximum slopes of storage
area walls may form part of the lease conditions. As a guide, they
should not exceed 3:1.
• Rotate discharge points to avoid areas of very fine tailings that are
difficult to traverse and revegetate.
• Where possible, treat tailings prior to discharge to remove or reduce
levels of toxicity.
• Examine pre-treatment processes for possible cost savings either by
recovery of fugitive materials in the waste or cost effective methods
for co-disposal e.g. neutralising acidic streams.
• Provide for the control of runoff from the tailings storage area and
external walls to protect them against erosion.
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6.2.1 Tailings Characterisation
The physical and chemical properties of tailings materials will determine
the extent to which vegetation of the tailings is practical and what other
options may need to be considered. Characteristics of tailings that
inhibit plant growth include:
• high concentration of heavy metals and salts;
• extremes of pH;
• lack of essential plant nutrients;
• lack of microbiological organisms;
• textural and structural characteristics which limit aeration and
infiltration;
• high levels of reflective light or heat absorption in light or dark
tailings causing physiological stress to vegetation; and
• physical damage by sand blast.
The extent to which these problems exist for any single tailings area will
need to be determined. Essential information required includes:
• particle size distribution;
• existing pH and likely changes in pH values over time;
• chemical demand (and likely cost) to achieve pH neutrality;
• level of heavy metals or other plant toxins;
• changes in toxicity levels likely with pH adjustment;
• in-situ water infiltration characteristics; and
• changes in physical and chemical properties with depth (at least in
likely root zone).
6.2.2 Treatment Options
• Permanent Water Cover
Where tailings have high sulfide levels and have potential to be
acid-forming or are slow to settle, the tailings disposal system may be
designed to provide for a permanent water cover. This approach
prevents the oxidation of the tailings and eliminates the need for
consolidation. It is essential that the disposal system be designed to
ensure that there is a permanent water cover but, at the same time,
avoiding seepage, overtopping etc. This technique has limited
application in Australia because of the generally high evaporation rates.
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