Tailings

Tailings are also called mine dumps, culm dumps, slimes, refuse, leach residue, slickens, or terra-cone (terrikon). ==Examples==

Sulfide minerals The effluent from the tailings from the mining of sulfidic minerals has been described as "the largest environmental liability of the mining industry". These tailings contain large amounts of pyrite (FeS2) and Iron(II) sulfide (FeS), which are rejected from the sought-after ores of copper and nickel, as well as coal. Although harmless underground, these minerals are reactive toward air in the presence of microorganisms, which if not properly managed lead to acid mine drainage. in a stream receiving acid mine drainage from surface coal mining Phosphate rock mining . These contain the waste byproducts of the phosphate fertilizer industry. Between 100 million and 280 million tons of phosphogypsum waste are estimated to be produced annually as a consequence of the processing of phosphate rock for the production of phosphate fertilizers. In addition to being useless and abundant, phosphogypsum is radioactive due to the presence of naturally occurring uranium, thorium, and their daughter isotopes. Depending on the price achievable on the uranium market, extraction of the uranium content may be economically lucrative even absent other incentives, such as reducing the harm the radioactive heavy metals do to the environment. Aluminium Bauxite tailings is a waste product generated in the industrial production of aluminium. Making provision for the approximately that is produced annually is one of the most significant problems in aluminium manufacturing. Red mud Coal ==Economics==

Early mining operations often did not take adequate steps to make tailings areas environmentally safe after closure. Modern mines, particularly those in jurisdictions with well-developed mining regulations and those operated by responsible mining companies, apply waste valorization to reprocessing waste materials, and often include the rehabilitation and proper closure of tailings areas in their costs and activities. For example, the Province of Quebec, Canada, requires not only the submission of a closure plan before the start of mining activity, but also the deposit of a financial guarantee equal to 100% of the estimated rehabilitation costs. Tailings dams are often the most significant environmental liability for a mining project. Mine tailings may have economic value in carbon sequestration due to the large exposed surface area of the minerals. ==Environmental concerns==

The fraction of tailings to ore can range from 90 to 98% for some copper ores to 20–50% of the other (less valuable) minerals. The rejected minerals and rocks liberated through mining and processing have the potential to damage the environment by releasing toxic metals (arsenic and mercury being two major culprits), by acid drainage (usually by microbial action on sulfide ores), or by damaging aquatic wildlife that rely on clear water (vs suspensions). One example is Cadmium, which is commonly found in zinc ores, can remain in mine tailings and waste water during refining process, causing toxicity to surrounding areas. 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. Other disasters caused by tailings dam failures are, the 2000 Baia Mare cyanide spill and the Ajka alumina plant accident. In 2015, the iron ore tailings dam failure at the Germano mine complex in Minas Gerais, Brazil, was the country's biggest environmental disaster. The dam breach caused the death of 19 people due to flooding of tailings slime downstream and affected some 400 km of the Doce river system with toxic effluence and out into the Atlantic Ocean. ==Human rights==

Tailings deposits tend to be located in rural areas or near marginalized communities, such as indigenous communities. The Global Industry Standard on Tailings Management (GISTM) recommends that "a human rights due diligence process is required to identify and address those that are most at risk from a tailings facility or its potential failure." ==Storage methods==

Historically, tailings were disposed of in the most convenient manner, such as in downstream running water or down drains. Because of concerns about these sediments in the water and other issues, tailings ponds came into use. 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. This slurry is 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. It is increasingly common for tailings storage facilities to require special barriers like bituminous geomembranes (BGMs) to contain liquid tailings slurries and prevent impact to the surrounding environment. 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. It was estimated in 2000 that there were about 3,500 active tailings impoundments in the world. 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 which potentially reduces the impacts on the environment in terms of a reduction in the potential seepage rates, space used, leaves the tailings in a dense and stable arrangement and eliminates the long-term liability that ponds leave after mining is finished. Although there are potential merits to dry stacked tailings, these systems are often cost prohibitive due to increased capital cost to purchase and install the filter systems and the increase in operating costs- generally associated electricity consumption and consumables (such as filter cloth) of such systems. 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. A common term for this is high-density paste fill (HDPF). HDPF is a more expensive method of tailings disposal than pond storage, however it has many other benefits as 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 riverine tailings disposal (RTD). 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 & Railway Company in Tasmania to the King River, or the poisoning from the Panguna mine on Bougainville Island, which led to large-scale civil unrest on the island, and the eventual permanent closing of the mine. If the density and temperature of the tailings product is not controlled, it may travel long distances, or even float to the surface. This method is used by the gold mine on Lihir Island; its waste disposal has been viewed by environmentalists as highly damaging, while the owners claim that it is not harmful. It is legal in Indonesia, Norway and Papua New Guinea. Planta de Pellets had in 2019 however pledged to end this practise by late 2023. 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 riverine disposal to cease. Considerable work remains to be done. However, co-disposal has been successfully implemented by several designers including AMEC at, for example, the Elkview Mine in British Columbia. Pond reclamation by microbiology During extraction of the oil from oil sand, tailings consisting of water, silt, clays, and other solvents are also created. This solid will become mature fine tailings by gravity. Foght et al (1985) estimated that there are 103 anaerobic heterotrophs and 104 sulfate-reducing prokaryotes per milliliter in the tailings pond, based on conventional most probable number methods. Foght set up an experiment with two tailings ponds and an analysis of the archaea, bacteria, and the gas released from tailings ponds showed that those were methanogens. As the depth increased, the moles of CH4 released actually decreased. Siddique (2006, 2007) states that methanogens 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 archaea and bacteria can degrade the naphtha, which was considered as waste 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, these methanogens improve the coefficient of utilization. Moreover, these methanogens change the structure of the tailings pond and help the pore water efflux to be reused for processing oil sands. Because the archaea and bacteria metabolize and release bubbles within the tailings, the pore water can go through the soil easily. Since they accelerate the densification of mature fine tailings, the tailings ponds are enabled to settle the solids more quickly so that the tailings can be reclaimed earlier. Moreover, the water released from the tailings can be used in the procedure of refining oil. Reducing the demand of water can also protect the environment from drought. 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. Even though the reprocessing of tailings might deliver additional metal value and decreases in some cases the risk for acid mine drainage, the volume of mineral waste is not decreased significantly. To remediate this, a valorization of the bulk of the tailings, the gangue minerals, has to be found. A crucial valorization pathway is the use in construction materials, which is the commodity with the highest demand for minerals. Novel technologies are being developed, such as granulation processes for the application as aggregate in concrete. A machine called the PET4K Processing Plant has been used in a variety of countries for the past 20 years to remediate contaminated tailings. ==International policy==

The UN and business communities developed an international standard for tailings management in 2020 after the critical failure of the Brumadinho dam disaster. The program was convened by United Nations Environment Programme (UNEP), International Council on Mining and Metals (ICMM) and the Principles for Responsible Investment. ==See also==