12.9 Tailings storage facilities
The main function of a tailing storage facility is the safe, long-term storage of process waste with minimal environmental or social impact. The design of each facility is specific to the mining operation and site conditions. The design life of tailings storage facility is effectively perpetuity, which means it should be able to survive in a stable form without human intervention. Tailings storage facilities are constructed over a long period and this must be reflected in the geotechnical stability evaluations.
Tailing storage facilities may be constructed using tailings sand or borrow materials for the embankment. The amount of coarse tailings material or suitable rock, as well as the regional seismicity, will govern the type of embankment constructed. The construction of the embankment is done in a series of lifts, during the operational life of the mine. Synthetic liners or compacted clay may be used to minimize seepage. The tailings are slurried via pipeline to the facility and deposited via a single point discharge, spigots or a cyclone, when the sand fraction is used to construct the embankment. In single point discharge and spigot systems, the tailings are usually deposited to form a beach against the embankment with the liquid collecting away from it. This reduces the seepage and increases the stability. The level of the tailings pond is controlled by decanting any surplus liquid, also referred to as supernatant. This can be done through an embankment drain, decant towers or a floating pump. The liquid is then returned to the processing plant or discharged.