Environmental Considerations
The elements and compounds uncovered and liberated through mining and processing, which are not usually part of the ecological systems (in such a form or concentration) have the potential to alter the receiving environment to its detriment. Most mining and minerals processing wastes contain minerals, such as sulphides, which are formed at higher temperatures and pressures at geological depth. When exposed to aerobic surficial conditions, or as a result of processing, minerals may breakdown releasing elements from their mineralogical bindings which may not be easily absorbed by unaccustomed ecosystems without impact (this process is sometimes known as Acid and Metalliferous Drainage). It is precisely because these elements did not interact with the overlying ecosystems before mining that they may pose issues to ecosystems and communities post-mining.
Disposal of mine tailings is one of the most important environmental issues for any mine during the project's life. While significant pressure is placed on mining projects in developed countries to conform to stringent environmental standards, many projects in developing nations do not take significant steps to prevent or mitigate environmental damage.
The sustainability challenge in the management of tailings and waste rock is to dispose of material, such that it is inert or, if not, stable and contained, to minimise water and energy inputs and the surface footprint of wastes and to move toward finding alternate uses.
Although ideally the tailings would be made up of gangue materials (i.e. silica), to some degree, the sought-after mineral also appears in the tailings. Tailings also commonly contain unmineralised sulphides that can breakdown and release metals and generate acidic conditions. In operations that recover lead, uranium and other toxic heavy metals, this represents a significant environmental hazard. In addition to the minerals themselves, some processing methods involve marine pollutants such as copper sulfate, xanthate or cyanide which will be present to some degree in the tailings. In some operations, components of the gangue may also be toxic, though it is rare for these materials to be present above trace levels. An example is thallium in sulfide ores.
In order to prevent the uncontrolled release of tailings material into the environment, mines usually have a disposal facility which quite often takes the form of a dam or pond. This is a convenient method of storage since tailings are often in the form of a slurry when they are discharged from the concentrator. These facilities often require the clearing of more land than the rest of the mine (including open-pit operations) combined, and failure of the wall can result in a massive release of tailings. As such they are of great environmental concern.
Tailings release and subsequent damage to the environment can also occur without catastrophic failure of the storage facility. These kinds of release are much less obvious and may take the form of acid drainage or dry tailings dust being blown away from the storage area. Several major environmental disasters have been caused by tailings dam failures and other release of tailings into the environment. Some examples are the Ok Tedi environmental disaster, the Buffalo Creek Flood, the 2000 Baia Mare cyanide spill and the Ajka alumina plant accident.
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