Tailings Disposal - Mining and the Environment: From Ore to Metal - page 733

Plant

Tailings
Delivery
Pipelines

Tailings
Thickeners Parimeter

Embankment

Existing
Cell 1

Existing
Cell 2

Booster
Pump Station

Water
Storage A

Outer Risers

Riser Feed
Lines

Independent
Central
Risers

Outer Risers

Diagram of the Centralized Discharged
Tailings Storage Facility

Water
Storage
Embankment

Risers Finished Tailings

Survey

Storm Water
Storage Area

Perimeter Ring
Main

Internal Catch
Embankment

Decant Sump
and Pump Station
Exaggerated Scale

in arid areas such as central Australia where tailings supernatant is evaporated, rather than
recycled. By contrast, in high rainfall areas, there is commonly an excess of liquid, so that,
even with recycling there is excess water which may require treatment, prior to release.
One of the important properties of any particular tailings is its 'beach angle' which is
the angle to the horizontal formed by the tailings solids as they deposit. The beach angle
depends on the nature of the tailings, particularly its particle sizes and the density and vis-
cosity of the slurry. Beach angles formed by under-water deposition are usually very low -
much less than 1º. However, densities formed by deposition above the pond level may
achieve 3º or more. The beach angle can be determined during feasibility studies and is an
important parameter in the design and operation of tailings impoundments.
Another important property of tailings is the settled density of solids that is achieved,
both initially and over time. In all cases, the higher the density that can be achieved, the
better. The main reason for this is that higher densities mean that more storage can be
achieved within the same volume. Higher densities also mean higher strength, which
is of critical importance if upstream or centreline constructions are used. Saturated tail-
ings may consolidate extremely slowly under their own weight. However, the surface of
tailings exposed to the atmosphere dessicates rapidly leading to widespread cracking but
with the intercrack soil 'slabs' having a much higher density than at the time of initial
exposure. The next layer of tailings i lls the cracks and adds an additional layer which,
on exposure also desiccates, and so on. In this way it is possible, except in areas where

FIGURE 18.12
Schematic East/West Section through
Storage Area Exaggerated Vertical
Scale

Thickened Tailings Discharge uses
tailings thickened to the maximum
extent consistent with being pumped.
The thickened tailings are discharged
from a riser located in the middle of
the tailings storage. The resulting tail-
ings deposit is in the form of a shallow
cone, which provides an attractive
landform, readily accessible and amena-
ble to rehabilitation.
Source:
ICME 1998