Tailings Disposal - Mining and the Environment: From Ore to Metal - page 714

TABLE 18.1
Typical Solid Concentrations for Various Tailings Types - Typical tailings slurries have solids contents of 20 to
40% by weight

Tailings Type Slurry % Solids Paste % Solids

Bauxite red mud 25 45

Base metal tailings 40 75

Coal tailings 25-30 —

Gold tailings 45 72

Mineral sands slimes 15 24

Nickel tailings 35 45

Source:
Williams (2004)

FIGURE 18.3
Simplifi ed Diagram of Cyanide
Degradation Processess in TSFs

UV
Light

Cyanide is generally considered as a
transient pollutant: its toxic proper-
ties decrease rapidly over time due to
natural degradation.
Source:
www.newmont.com

Volatization

Cyanite Biodegradation

CN in
TAILINGS

Photochemical

Nitrate

Ammonia

EMBANKMENT (aerobic)

Hydrolysis React

with
Sulphur

Thiocyanate

Precipitation
of Metal
Complexes

NATURAL SOIL

Tailings from gold mines commonly contain residual cyanide, as discussed in more detail
in Chapter Six in this topic. Cyanide attenuation refers to the various processes that decrease
the concentration of cyanide in solution, whether in the natural environment or in engi-
neered facilities (ICME 1999). Cyanide is generally considered as a transient pollutant: its
toxic properties decrease rapidly over time due to natural degradation of cyanide caused by
volatilization, photodecomposition, bio-decomposition and conversion to thiocyanate as illus-
trated in Figure 18.3 . Cyanide attenuation, its decay and transformation, is generally very
effective in reducing cyanide concentrations in the tailings impoundment. However, there
are circumstances where cyanide decomposition and attenuation occur much more slowly.

Cyanide attenuation, its decay
and transformation, is generally
very effective in reducing cyanide
concentrations in the tailings
impoundment.