Environmental Engineering Reference
In-Depth Information
STAGE 7
STAGE 6
STAGE 5
STAGE 4
STAGE 3
STAGE 2
1 m
1 m
6 m
6 m
STAGE 1 (6,2 m)
Filter
blanket
with drains
2
2.5
1
1
ZONE C
ZONE C
Cutoff
Trench
(Depth Varies)
Low
permeability
layer
Drainage
Collection
FIGURE 18.13
Tailings Embankment for Staged
Construction
ZONE A : Low permeability fill
ZONE B : Filter zone
ZONE C : Backfill - mine waste
precipitation exceeds evaporation all year, for signii cant increases in density to be achieved.
For example, a common initial settled density may be 0.9 to 1.0 T/m 3 (dry density), while
after repeated cycles of deposition and exposure, densities of 1.3 T/m 3 or more may be
achieved.
Tailings Discharge Systems
Tailings discharge systems are designed and operated to distribute the tailings so that it
accumulates as planned, and to provide a pool of clear water (the 'decant pool or pond')
from which the supernatant water is decanted and returned to the mill for re-use. For a
long, narrow impoundment such as many valley impoundments, discharge may be from
one or two locations at one end of the storage with a decant pool at the other end. For
a broader impoundment, discharge is usually through multiple spigots located around
the perimeter of the storage. Spigots are opened and closed to provide a more or less even
accumulation of tailings within the impoundment and also to coni ne the decant pool in its
intended location.
Tailings are sometimes segregated before being discharged to an impoundment.
Cyclones may be used to extract the sand fraction from the run-of-the-mill tailings, and
then used to raise the embankment or as backi ll in underground workings. The remain-
ing i nes or slimes are then deposited via pipes or spigots into the impoundment.
Control of the decant pool is an important management procedure for most TSFs.
Inadequate control may result in the reduction of free-board and hence increase the risk of
overtopping; in the decant pool encroaching the embankment and hence increasing pore pres-
sure; in high seepage rates and in embankment settlement (Engels and Dixon-Hardy 2004) - all
of these are potential contributors to impoundment failure. Generally, the aim is to minimize
the size of the decant pool, consistent with producing a clear decant. Accordingly, regular
monitoring of the decant pool is required to operate a TSF safely and effectively.
Regular monitoring of the decant
pool is required to operate a TSF
safely and effectively.
 
 
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