Tailings

Tailings

Overview

Tailings, also called mine dumps, slimes, tails, leach residue, or slickens, are the materials left over after the process of separating the valuable fraction from the uneconomic fraction (gangue
Gangue
In mining, gangue is the commercially worthless material that surrounds, or is closely mixed with, a wanted mineral in an ore deposit. The separation of mineral from gangue is known as mineral processing, mineral dressing or ore dressing and it is a necessary and often significant aspect of mining...

) of an ore
Ore
An ore is a type of rock that contains minerals with important elements including metals. The ores are extracted through mining; these are then refined to extract the valuable element....

. Tailings are distinct from overburden
Overburden
Overburden is the material that lies above an area of economic or scientific interest in mining and archaeology; most commonly the rock, soil, and ecosystem that lies above a coal seam or ore body. It is also known as 'waste' or 'spoil'...

 or waste rock, which are the materials overlying an ore or mineral body that are displaced during mining without being processed.

The extraction of minerals from ore can be done two ways: placer mining
Placer mining
Placer mining is the mining of alluvial deposits for minerals. This may be done by open-pit or by various surface excavating equipment or tunneling equipment....

, which uses water and gravity to extract the valuable minerals, or hard rock mining
Hard rock mining
Underground hard rock mining refers to various underground mining techniques used to excavate hard minerals, mainly those containing metals such as ore containing gold, silver, iron, copper, zinc, nickel and lead, but also involves using the same techniques for excavating ores of gems such as...

, which uses pulverization of rock, then chemicals.
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Tailings, also called mine dumps, slimes, tails, leach residue, or slickens, are the materials left over after the process of separating the valuable fraction from the uneconomic fraction (gangue
Gangue
In mining, gangue is the commercially worthless material that surrounds, or is closely mixed with, a wanted mineral in an ore deposit. The separation of mineral from gangue is known as mineral processing, mineral dressing or ore dressing and it is a necessary and often significant aspect of mining...

) of an ore
Ore
An ore is a type of rock that contains minerals with important elements including metals. The ores are extracted through mining; these are then refined to extract the valuable element....

. Tailings are distinct from overburden
Overburden
Overburden is the material that lies above an area of economic or scientific interest in mining and archaeology; most commonly the rock, soil, and ecosystem that lies above a coal seam or ore body. It is also known as 'waste' or 'spoil'...

 or waste rock, which are the materials overlying an ore or mineral body that are displaced during mining without being processed.

The extraction of minerals from ore can be done two ways: placer mining
Placer mining
Placer mining is the mining of alluvial deposits for minerals. This may be done by open-pit or by various surface excavating equipment or tunneling equipment....

, which uses water and gravity to extract the valuable minerals, or hard rock mining
Hard rock mining
Underground hard rock mining refers to various underground mining techniques used to excavate hard minerals, mainly those containing metals such as ore containing gold, silver, iron, copper, zinc, nickel and lead, but also involves using the same techniques for excavating ores of gems such as...

, which uses pulverization of rock, then chemicals. In the latter, the extraction of minerals from ore requires that the ore be ground into fine particles, so tailings are typically small and range from the size of a grain of sand to a few micrometres. Mine tailings are usually produced from the mill
Mill (grinding)
A grinding mill is a unit operation designed to break a solid material into smaller pieces. There are many different types of grinding mills and many types of materials processed in them. Historically mills were powered by hand , working animal , wind or water...

 in slurry
Slurry
A slurry is, in general, a thick suspension of solids in a liquid.-Examples of slurries:Examples of slurries include:* Lahars* A mixture of water and cement to form concrete* A mixture of water, gelling agent, and oxidizers used as an explosive...

 form (a mixture of fine mineral particles and water).

Tailings represent an external cost of mining, and this is particularly true of early mining operations which did not take adequate steps to make tailings areas environmentally safe after closure. Modern day mines, particularly in jurisdictions with well-developed mining regulations and/or operated by responsible mining companies, incorporate the rehabilitation and proper closure of tailings areas in the mining costs and activities. For example, the province of Quebec, Canada, requires not only submission of closure plan before the start of mining activity, but also the deposit of a financial guarantee equal to 70% of the estimated rehabilitation costs. Tailings dams are often the most significant environmental liability for a mining project.

When applied to coal
Coal mining
The goal of coal mining is to obtain coal from the ground. Coal is valued for its energy content, and since the 1880s has been widely used to generate electricity. Steel and cement industries use coal as a fuel for extraction of iron from iron ore and for cement production. In the United States,...

 and oil sands mining
Tar sands
Bituminous sands, colloquially known as oil sands or tar sands, are a type of unconventional petroleum deposit. The sands contain naturally occurring mixtures of sand, clay, water, and a dense and extremely viscous form of petroleum technically referred to as bitumen...

, the term 'tailings' refers specifically to fine waste suspended in water.

Tailings composition


The composition of tailings is directly dependent on the composition of the ore and the process of mineral extraction used on the ore.

Certain types of extraction process, like heap leaching
Heap leaching
Heap leaching is an industrial mining process to extract precious metals, copper, uranium, and other compounds from ore.The process has ancient origins; one of the classical methods for the manufacture of copperas was to heap up iron pyrite and collect the leachate from the heap, which was then...

 for example, may result in quantities of chemicals used to perform the leaching remaining in the material once leaching has been completed. Older forms of mineral extraction, such as those utilised during the early gold boom years of Australian gold mining, resulted in large heaps of fine tailings being left dotted around the landscape. These tailings dumps would continue to leach residual chemicals into the environment, and if weather conditions allowed it the finer fraction would become windborne, blowing around the townships surrounding the now-dormant mining areas.

Typically, the bulk quantity of a tailings product will be barren rock, crushed and ground to a fine size ranging from coarse sands down to a talcum powder consistency.

Tailings may contain trace quantities of metals found in the host ore, and they may contain substantial amounts of added compounds used in the extraction process. Elements are rarely in elemental form, more often as complex compounds.

Common minerals and elements found in tailings include
  • Arsenic
    Arsenic
    Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...

     - Found in association with gold ores
  • Barite
    Barite
    Baryte, or barite, is a mineral consisting of barium sulfate. The baryte group consists of baryte, celestine, anglesite and anhydrite. Baryte itself is generally white or colorless, and is the main source of barium...

  • Calcite
    Calcite
    Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...

  • Fluorite
    Fluorite
    Fluorite is a halide mineral composed of calcium fluoride, CaF2. It is an isometric mineral with a cubic habit, though octahedral and more complex isometric forms are not uncommon...

  • Radioactive materials - Naturally present in many ores
  • Mercury
    Mercury (element)
    Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

  • Sulfur
    Sulfur
    Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

     - Forms many sulfide compounds / pyrites
  • Cadmium
    Cadmium
    Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Similar to zinc, it prefers oxidation state +2 in most of its compounds and similar to mercury it shows a low...

  • Hydrocarbons - Introduced by mining and processing equipment (oils & greases)


Common additives found in tailings
  • Cyanide
    Cyanide
    A cyanide is a chemical compound that contains the cyano group, -C≡N, which consists of a carbon atom triple-bonded to a nitrogen atom. Cyanides most commonly refer to salts of the anion CN−. Most cyanides are highly toxic....

     - as both sodium cyanide (NaCN) and hydrogen cyanide (HCN). Leaching agent in extremely dilute quantities which readily volatize upon exposure to sunlight.
  • SEX - Sodium Ethyl Xanthate
    Xanthate
    Xanthate usually refers to a salt with the formula ROCS2-M+ . The name xanthates is derived from Greek ξανθός , meaning “yellowish, golden”, and indeed most xanthate salts are yellow...

    . Flotation agent.
  • PAX - Potassium Amyl Xanthate. Flotation agent.
  • MIBC - Methyl Isobutyl Carbinol. Frothing agent.
  • Sulfamic acid
    Sulfamic acid
    Sulfamic acid, also known as amidosulfonic acid, amidosulfuric acid, aminosulfonic acid, and sulfamidic acid, is a molecular compound with the formula H3NSO3...

     - Cleaning / descaling agent.
  • Sulfuric acid
    Sulfuric acid
    Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...

     - Used in large quantities in the PAL
    PAL
    PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...

     process (Pressure Acid Leaching).
  • Activated Carbon
    Activated carbon
    Activated carbon, also called activated charcoal, activated coal or carbo activatus, is a form of carbon that has been processed to make it extremely porous and thus to have a very large surface area available for adsorption or chemical reactions.The word activated in the name is sometimes replaced...

     - Used in CIP (Carbon In Pulp
    Carbon in pulp
    Carbon in Pulp is an extraction technique for recovery of gold which has been liberated into a cyanide solution as part of the gold cyanidation process....

    ) and CIL (Carbon In Leach) processes.
  • Calcium
    Calcium
    Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

     - Different compounds, introduced as lime
    Lime (mineral)
    Lime is a general term for calcium-containing inorganic materials, in which carbonates, oxides and hydroxides predominate. Strictly speaking, lime is calcium oxide or calcium hydroxide. It is also the name for a single mineral of the CaO composition, occurring very rarely...

     to aid in pH control.


Tailings present a long term cost to the mining industry. If the company leaves or goes bankrupt, the local government can find itself with responsibility for the maintenance and monitoring of tailings dumps essentially forever - this, and other costs of cleanup, can impose liabilities that were estimated at up to 12 billion dollars in the US alone in 2005.

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 Metaliferous 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
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...

, uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

 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
Xanthate
Xanthate usually refers to a salt with the formula ROCS2-M+ . The name xanthates is derived from Greek ξανθός , meaning “yellowish, golden”, and indeed most xanthate salts are yellow...

 or cyanide
Cyanide
A cyanide is a chemical compound that contains the cyano group, -C≡N, which consists of a carbon atom triple-bonded to a nitrogen atom. Cyanides most commonly refer to salts of the anion CN−. Most cyanides are highly toxic....

 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
Thallium
Thallium is a chemical element with the symbol Tl and atomic number 81. This soft gray poor metal resembles tin but discolors when exposed to air. The two chemists William Crookes and Claude-Auguste Lamy discovered thallium independently in 1861 by the newly developed method of flame spectroscopy...

 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
Dam
A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are...

 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
Catastrophic failure
A catastrophic failure is a sudden and total failure of some system from which recovery is impossible. Catastrophic failures often lead to cascading systems 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
Ok Tedi Environmental Disaster
The Ok Tedi environmental disaster, due to the annual discharge of millions of tons of mining waste, has harmed the environment and livelihood of 50,000 people who live on or near the Ok Tedi River in Papua New Guinea...

, the Buffalo Creek Flood
Buffalo Creek Flood
The Buffalo Creek Flood was a disaster that occurred on February 26, 1972, when the Pittston Coal Company's coal slurry impoundment dam #3, located on a hillside in Logan County, West Virginia, USA, burst four days after having been declared 'satisfactory' by a federal mine inspector.The resulting...

, the 2000 Baia Mare cyanide spill
2000 Baia Mare cyanide spill
The 2000 Baia Mare cyanide spill was a leak of cyanide near Baia Mare, Romania, into the Someş River by the gold mining company Aurul, a joint-venture of the Australian company Esmeralda Exploration and the Romanian government....

 and the Ajka alumina plant accident
Ajka alumina plant accident
The Ajka alumina sludge spill was an industrial accident at a caustic waste reservoir chain of the Ajkai Timföldgyár alumina plant in Ajka, Veszprém County, in western Hungary...

.

Continuum



Historically, tailings were disposed of however was convenient, such as in downstream running water or down drain
Drain
A drain is a plumbing fixture that provides an exit-point for waste water or water that is to be re-circulatedDrain may also refer to:* Drainage, the natural or artificial removal of surface and sub-surface water from a given area...

s. Because of concerns about these sediments in the water and other issues, tailings ponds began to be constructed, which were bounded by impoundments (an impoundment is a dam). These dams typically use "local materials" including the tailings themselves, and may be considered embankment dam
Embankment dam
An embankment dam is a massive artificial water barrier. It is typically created by the emplacement and compaction of a complex semi-plastic mound of various compositions of soil, sand, clay and/or rock. It has a semi-permanent waterproof natural covering for its surface, and a dense, waterproof...

s. Traditionally, the only option for tailings storage was to deal with a tailings slurry. This slurry was a dilute stream of the tailings solids within water that was sent to the tailings storage area. The modern tailings designer has a range of tailings products to choose from depending upon how much water is removed from the slurry prior to discharge. The removal of water not only can create a better storage system in some cases (e.g. dry stacking, see below) but can also assist in water recovery which is a major issue as many mines are in arid regions. In a 1994 description of tailings impoundments, however, the U.S. EPA stated that dewatering methods may be prohibitively expensive except in special circumstances. Subaqueous storage of tailings has also been used.

Pond storage


Tailing ponds are areas of refused mining
Mining
Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...

 tailings where the water borne refuse material is pumped into a pond
Pond
A pond is a body of standing water, either natural or man-made, that is usually smaller than a lake. A wide variety of man-made bodies of water are classified as ponds, including water gardens, water features and koi ponds; all designed for aesthetic ornamentation as landscape or architectural...

 to allow the sedimentation
Sedimentation
Sedimentation is the tendency for particles in suspension to settle out of the fluid in which they are entrained, and come to rest against a barrier. This is due to their motion through the fluid in response to the forces acting on them: these forces can be due to gravity, centrifugal acceleration...

 (meaning separation) of solid particles from the water. The pond is generally impounded with a dam, and known as tailings impoundments or tailings dams. It was estimated in 2000 that there were about 3,500 active tailings impoundments in the world. The ponded water is of some benefit as it minimizes fine tailings from being transported by wind into populated areas where the toxic chemicals could be potentially hazardous to human health; however, it is also harmful to the environment. Tailing ponds are often somewhat dangerous because they attract wildlife such as waterfowl or caribou as they appear to be a natural pond, but they can be highly toxic and harmful to the health of these animals. Tailings ponds are used to store the waste made from separating minerals from rocks, or the slurry produced from oil sands mining. Tailings are sometimes mixed with other materials such as bentonite
Bentonite
Bentonite is an absorbent aluminium phyllosilicate, essentially impure clay consisting mostly of montmorillonite. There are different types of bentonite, each named after the respective dominant element, such as potassium , sodium , calcium , and aluminum . Experts debate a number of nomenclatorial...

 to form a thicker slurry that slows the release of impacted water to the environment.

There are many different subsets of this method, including valley impoundments, ring dikes, in-pit impoundments, and specially dug pits. The most common is the valley pond, which takes advantage of the natural topographical depression in the ground. Large earthen dams may be constructed and then filled with the tailings. Exhausted open pit mines may be refilled with tailings. In all instances, due consideration must be made to contamination of the underlying water table, amongst other issues. Dewatering is an important part of pond storage, as the tailings are added to the storage facility the water is removed - usually by draining into decant tower structures. The water removed can thus be reused in the processing cycle. Once a storage facility is filled and completed, the surface can be covered with topsoil and revegetation commenced. However, unless a non-permeable capping method is used, water that infiltrates into the storage facility will have to be continually pumped out into the future.

The biggest danger of tailings ponds is dam failure, with the most publicized failure in the US being the failure of a coal slurry dam in the West Virginia
West Virginia
West Virginia is a state in the Appalachian and Southeastern regions of the United States, bordered by Virginia to the southeast, Kentucky to the southwest, Ohio to the northwest, Pennsylvania to the northeast and Maryland to the east...

 Buffalo Creek disaster, which killed 125 people; other collapses include the Ok Tedi environmental disaster on New Guinea
New Guinea
New Guinea is the world's second largest island, after Greenland, covering a land area of 786,000 km2. Located in the southwest Pacific Ocean, it lies geographically to the east of the Malay Archipelago, with which it is sometimes included as part of a greater Indo-Australian Archipelago...

, which destroyed the fishery of the Ok Tedi River
Ok Tedi River
The Ok Tedi is a river in New Guinea. The Ok Tedi Mine is located near the headwaters of the river, which is sourced in the Star Mountains. Nearly the entirety of the river runs through the North Fly District of the Western Province of Papua New Guinea, but the river crosses the international...

. On the average, worldwide, there is one big accident involving a tailings dam each year. Tailings ponds can also be a source of acid drainage, leading to the need for permanent monitoring and treatment of water passing through the tailings dam; the cost of mine cleanup has typically been 10 times that of mining industry estimates when acid drainage was involved.

Dry stacking


Tailings do not have to be stored in ponds or sent as slurries into oceans, rivers or streams. There is a growing use of the practice of dewatering tailings using vacuum or pressure filters so the tailings can then be stacked. This saves water, reduces the impacts on the environment in terms of space used, leaves the tailings in a dense and stable arrangement and eliminates the long-term liability that ponds leave after mining is finished.

Storage in underground workings


While disposal into exhausted open pits is generally a straightforward operation, disposal into underground voids is more complex. A common modern approach is to mix a certain quantity of tailings with waste aggregate and cement, creating a product that can be used to backfill underground voids and stopes
Stoping (mining method)
Stoping is the removal of the wanted ore from an underground mine leaving behind an open space known as a stope. Stoping is used when the country rock is sufficiently strong not to cave into the stope, although in most cases artificial support is also provided...

. A common term for this is HDPF - High Density Paste Fill. HDPF is a more expensive method of tailings disposal than pond storage, however it has many other benefits – not just environmental but it can significantly increase the stability of underground excavations by providing a means for ground stress to be transmitted across voids - rather than having to pass around them – which can cause mining induced seismic events like that suffered previously at the Beaconsfield Mine Disaster

Riverine tailings


Usually called RTD – Riverine Tailings Disposal. In most environments, not a particularly environmentally sound practice, it has seen significant utilisation in the past, leading to such spectacular environmental damage as done by the Mount Lyell Mining and Railway Company
Mount Lyell Mining and Railway Company
Mount Lyell Mining and Railway Company was a Tasmanian mining company formed on the 29 March 1893, most commonly referred to as Mount Lyell. Mount Lyell was the dominant copper mining company of the West Coast from 1893 to 1994, and was based in Queenstown, Tasmania.Following consolidation of...

 in Tasmania
Tasmania
Tasmania is an Australian island and state. It is south of the continent, separated by Bass Strait. The state includes the island of Tasmania—the 26th largest island in the world—and the surrounding islands. The state has a population of 507,626 , of whom almost half reside in the greater Hobart...

 to the King River
King River (Tasmania)
- Upper reaches :It rises in the vicinity of the Eldon Range, passes through the West Coast Range between Mount Huxley and Mount Jukes and empties in Macquarie Harbour near Strahan....

, or the poisoning from the Panguna
Panguna
Panguna is a town and a copper mine on Bougainville Island, Papua New Guinea. By the end of its operations on May 15, 1989 it was the largest open-cut mine in the world; it was also a major catalyst in the unrest in Bougainville in the 1970s and 1980s.- See also :* History of Bougainville*...

 mine on Bougainville Island
Bougainville Island
Bougainville Island is the main island of the Autonomous Region of Bougainville of Papua New Guinea. This region is also known as Bougainville Province or the North Solomons. The population of the province is 175,160 , which includes the adjacent island of Buka and assorted outlying islands...

, which led to large-scale civil unrest on the island, and the eventual permanent closing of the mine.

As of 2005, only three mines operated by international companies continued to use river disposal: The Ok Tedi mine
Ok Tedi Mine
The Ok Tedi Mine is an open-pit copper and gold mine located near the headwaters of the Ok Tedi River, in the Star Mountains Rural LLG of the North Fly District of the Western Province of Papua New Guinea...

, the Grasberg mine
Grasberg mine
The Grasberg Mine is the largest gold mine and the third largest copper mine in the world. It is located in the province of Papua in Indonesia near Puncak Jaya, the highest mountain in Papua, and it has 19,500 employees...

 and the Porgera mine
Porgera Gold Mine
The Porgera Gold Mine is a large gold and silver mining operation in Enga province, Papua New Guinea , located at the head of the Porgera Valley. The mine is situated in the rain forest covered highlands at an altitude of 2,200 to 2,700 m, in a region of high rainfall, landslides, and frequent...

, all on New Guinea. This method is used in these cases due to seismic activity and landslide dangers which make other disposal methods impractical and dangerous.

Submarine tailings


Commonly referred to as STD (Submarine Tailings Disposal) or DSTD (Deep Sea Tailings Disposal). Tailings can be conveyed using a pipeline then discharged so as to eventually descend into the depths. Practically, it is not an ideal method, as the close proximity to off-shelf depths is rare. When STD is used, the depth of discharge is often what would be considered shallow, and extensive damage to the seafloor can result due to covering by the tailings product. It is also critical to control the density and temperature of the tailings product, to prevent it from travelling long distances, or even floating to the surface. The Solwara project being commenced in the Bismarck Sea
Bismarck Sea
The Bismarck Sea lies in the southwestern Pacific Ocean to the north of the island of Papua New Guinea and to the south of the Bismarck Archipelago and Admiralty Islands. Like the Bismarck archipelago, it is named in honour of the German chancellor Otto von Bismarck...

 by Nautilus Minerals
Nautilus Minerals
Nautilus Minerals Inc. is an underwater mining company headquartered in Toronto, Canada. They are commencing copper and platinum group metals mineral production utilizing a newly constructed mining ship in the territorial waters of Papua New Guinea....

 proposes to use a modified STD method back down to depths below 1500 metres.

This method is used by the gold mine on Lihir Island
Lihir Island
Lihir Island is the largest island in the Lihir group of islands, 22 km long and 14.5 km wide, in Papua New Guinea's New Ireland Province. It consists of a complex of several overlapping basaltic stratovolcanoes rising 700m above sea level. While the volcanoes are not currently active,...

; its waste disposal has been viewed by environmentalists as highly damaging, while the owners claim that it is not harmful.

Phytostabilisation


Phytostabilisation is a form of phytoremediation
Phytoremediation
Phytoremediation Phytoremediation Phytoremediation (from the Ancient Greek , and Latin (restoring balance or remediation) describes the treatment of environmental problems (bioremediation) through the use of plants that mitigate the environmental problem without the need to excavate the...

 that uses plants for long-term stabilisation and containment of tailings, by sequestering pollutants in soil near the roots. The plant's presence can reduce wind erosion, or the plant's roots can prevent water erosion, immobilise metals by adsorption or accumulation, and provide a zone around the roots where the metals can precipitate and stabilise. Pollutants become less bioavailable and livestock, wildlife, and human exposure is reduced. This approach can be especially useful in dry environments, which are subject to wind and water dispersion. New work is also being done by Pan Pacific in the development of algal sequestration for plutonium and uranium tailings.

Different methods


Considerable effort and research continues to be made into discovering and refining better methods of tailings disposal. Research at the Porgera Gold Mine is focusing on developing a method of combining tailings products with coarse waste rock and waste muds to create a product that can be stored on the surface in generic-looking waste dumps or stockpiles. This would allow the current use of rivering disposal to cease. Considerable work remains to be done. However, co-disposal has been successfully implemented by several designers including AMEC
AMEC
AMEC plc is a global consultancy, engineering and project management company headquartered in London, United Kingdom. It is focused on the oil and gas, minerals and metals, renewable energy, environment and infrastructure sectors and has offices in 40 countries worldwide...

 at, for example, the Elkview Mine in British Columbia.

Tailings reprocessing


As mining techniques and the price of minerals improve, it is not unusual for tailings to be reprocessed using new methods, or more thoroughly with old methods, to recover additional minerals. Extensive tailings dumps of Kalgoorlie / Boulder in Western Australia were re-processed profitably in the 1990s by KalTails Mining.

Tailings pond reclamation by microbiology


During extracting the oil in the oil sand, tailings comprising by water, silt, clays and other solvents are also created. This solid will become the mature fine tailings (MFT) by the gravity. By using conventional most probable number (MPN) methods, Dr. Foght estimates that there are 10^3 anaerobic heterotrophs, 10^4 sulfate-reducing prokaryotes per militaries in the tailings pond (Foght et al. 1985). Foght sets up an experiment two tailings ponds. By analyzing the Achaeans, Bacteria and the gas released from tailings ponds, those are methanogenesis. As the depth increase, the moles of CH4 released are actually decreasing. Siddique (2006, 2007) states that methanogenesis in the tailings pond live and reproduce by anaerobic degradation which will lower the molecular weight from naphtha to aliphatic, aromatic hydrocarbons, carbon dioxide and methane. Those Achaeans and Bacteria can degrade the naphtha which was considered as wastes during the procedure of refining oil. Both of those degraded products are useful. Aliphatic, aromatic hydrocarbons and methane can be used as fuel in the humans’ daily lives. In other words, those methanogenesis improve the coefficient of utilization. Moreover, these methanogenesis change the structure of the tailings pond and help the pore water efflux to reuse for processing oil sands. Because the Achaeans and Bacteria metabolize and release bubble within the tailings, the pore water can go through the soil easily. Since they accelerate the densification of the mature fine tailings, the tailings pond are enable to settle the solids more quickly so that the tailings can be reclaimed earlier. Moreover, the water released from the tailings can use it in the procedure of refining oil. Reducing the demand of water can also protect the environment from drought.  

See also

  • Coal slurry impoundment
  • Mine closure planning
    Mine closure planning
    Mine closure planning involves planning effectively for the after-mining landscape – all activities required before, during, and after the operating life of a mine that are needed to produce an acceptable landscape economically...

  • Mine reclamation
    Mine reclamation
    Mine reclamation is the process of creating useful landscapes that meet a variety of goals, typically creating productive ecosystems from mined land...

  • Spoil tip

External links