Tailings Disposal - Mining and the Environment: From Ore to Metal - page 736

Perimeter Sump
Perimeter sumps are used in the case of central discharge system storages and a few other
cases where relatively little water is available for recycling.

Operating Considerations
Operating requirements vary from case to case. However, the most common are:
●

Managing the discharge and decant systems so that the decant water is clear; i.e. it con-
tains no tailings solids.

●

Consistent with the above requirement, to minimize the pool area, thereby maximiz-
ing the area of exposed tailings beaches.

●

Achieving a relatively uniform accumulation of tailings around the perimeter of the
impoundment.

●

In some cases where the tailings embankments are not designed as water retention
structures, avoidance of the decant pool encroaching on any part of the embankment.

●

In other cases (e.g. the tailings/water storage for the Dizon Copper Project in Zambales,
Philippines), the tailings impoundment also serves as the major water storage for the
project. In such cases, water storage considerations take precedence over optimization of
tailings solids storage, the solids settle sub-aqueously and remain covered by water.

●

Commonly, l occulant is added to the tailings stream to assist in settling of i ne tailings
particles and to maintain a clear decant.

Segregation of Tailings
As previously mentioned, tailings particles discharged as slurry into conventional tailings
impoundments, will segregate as they deposit, due to the higher settling rates of larger
particles. As a result, coarser particles and any denser minerals will tend to deposit close to
the discharge point(s), with successively i ner particles depositing at increasing distances.
The i nest materials (slimes) will generally underlie the decant pond. A tailings deposit
with distinct segregation and permeability zones develops (Kealy and Bush 1971) ( Figure
18.14 ). The slimes fraction of the tailings can be retrieved and applied to areas of an
impoundment that have high permeability zones that are causing seepage problems. The
blending will help to lower the permeability of the deposit.

Coarser particles and any denser
minerals will tend to deposit
close to the discharge point(s),
with successively fi ner particles
depositing at increasing distances.

FIGURE 18.14
Tailings Segregation Zones and Soil
Characteristics as a Function of
Distance from Spilling Location

ZONE 3
Low Permeability
Slimes

ZONE 2
Intermediate
Permeability

ZONE 1
High Permeability
Sand

The coarser fraction tends to settle
out closer to the tailings discharge
system and the slimes travel furthest
away generally towards the decant
pool. A tailings deposit with distinct
segregation and permeability zones
develops.
Source:
Based on Schoenhardt 2004 and ATV-DVWK-M503
2001

Decant Pool Dam

Content of Fine Grain

Grain Size

Density

Permeability

Shear Strength