Environmental Engineering Reference
In-Depth Information
FIGURE 18.16
Freeboard of a Tailings Facility
Explained
Pond level after 1000y, 72 hr
rainfall event (no decant
operational)
Embankment Crest
Operational Freeboard
The total freeboard is defi ned as the
vertical height between the waterline
and the inside top of the embankment
crest comprising beach freeboard and
operational freeboard.
Source:
DME 1999
Total
Beach Freeboard
Beach
Decant
Pool
Tailings
Human and Environmental Risk
Even in remote areas, human settlements or human land use occur close to the mine and
the impacts of tailings disposal facilities on the public and environment must be mini-
mized. Tailings disposal sites near villages, future townships, lakes and karst topography
or limestone, where leakage may be an issue, are best avoided. Similarly, siting of tailings
impoundments above underground mine workings is also best avoided.
Tailings disposal sites near villages,
future townships, lakes and karst
topography or limestone, where
leakage may be an issue, are best
avoided.
Distance and Elevation Relative to the Process Plant
Proximity to the process plant is an important factor, with a location at a lower elevation
being advantageous so as to enable discharge by gravity. As such, distance from, and eleva-
tion relative to the process plant have a signii cant impact on the operating cost. Tailings
storage facilities located a long distance from the process plant require long and costly
tailings and decant water pipelines. Tailings storage facilities located well above the proc-
ess plant or where the tailings discharge line traverses elevated terrain incur signii cant
expenditure on pumping stations and pump operation costs.
Distance from, and elevation
relative to, the process plant
have a signifi cant impact on the
operating cost.
Storage Capacity and Tailings
An ideal tailings disposal site should have a topography which achieves the maximum
storage capacity with a minimum amount of embankment i ll and therefore construc-
tion cost. The i ll efi ciency ratio (dei ned as the ratio between the storage capacity and
embankment i ll volume) is used to quantify this aspect of the tailings storage facility. As
there is usually some degree of uncertainty with respect to the required storage volume,
the topography should be sufi cient to permit the tailings dam embankment to be raised
to meet potential extra storage capacity requirements. In many situations however, it is not
possible to contain all tailings within a single impoundment. It is therefore common for
mining projects to have more than one TSF.
An ideal tailings disposal site
should have a topography which
achieves the maximum storage
capacity with a minimum amount
of embankment fi ll.
Embankment Height
Sub-grade disposal into abandoned mine voids warrants serious consideration wherever
such voids are available. However, this may be precluded if there are existing active under-
ground workings nearby or if there is potential for future underground mining below the
candidate voids. Several catastrophic events have resulted from the l ow of tailings into
active underground mines (e.g. the Mufulira disaster in Zambia in 1970). In most cases,
however, there will be no suitable voids, and the tailings impoundment must be formed
by the construction of one or more embankments. Ideally in addition to having a small
volume, embankments should be kept as low as possible. In a seismically active area, high
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