Information about Tailings
Tailings (also known as tailings pile, tails, leach residue, or slickens[1]) are the materials left over[2] after the process of separating the valuable fraction from the worthless fraction of an ore.
Tailings represent external costs of mining. 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. Yesterday's tails can be tomorrow's resource, as seen during the 1990s when the extensive tailings dumps of Kalgoorlie / Boulder in Western Australia were re-processed profitably by KalTails Mining.
In coal and oil sands mining, the word 'tailings' refers specifically to fine waste suspended in water.
Certain types of extraction process, like heap leaching 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 quantities of heavy metals found in the host ore, and they may contain added chemicals used in the extraction process. Elements are rarely in elemental form, more often as complex compounds.
Common minerals and elements found in Tailings
There is, however, a strong push from the leading mining houses and their design consultants to support the cessation of unsustainable tailings disposal practises. Unsustainable, in the sense that continuing to blatantly pollute the local environment damages a mining company's social license to operate, and by default damages the social licenses of all mining companies. It is in the mining industry's best interests to support efforts to prevent and halt non-sustainable tailings disposal methods.
Reprocessing of old tailings dumps and dams has assisted in the cleaning up of legacy tailings dumps, with the reproccessed tailings being disposed of using a more effective method than a simple surface dump.
Designing for Geochemical Issues
Geochemical issues have become highly prominent as severe acid generation problems became apparent at a number of mature mines around the world. Some of these mines, which had been operated by smaller mining companies, became orphan sites, leaving significant legacies for future generations. The majority of the acid drainage mine sites have become very expensive legacies for the major mining companies that owned them. It has been necessary to develop and operate acid drainage collection and treatment systems for continued operation and closure of numerous mines. Capital costs for ARD collection and treatment systems have been in the several tens of millions of dollars, with ongoing operating costs up to several millions of dollars annually. As a result, companies developing new mines have focussed on methods to predict and prevent or reduce acid generation from tailings.
Considerable research, for example CANMET's Mine Effluent Neutral Drainage (MEND) program, was carried out in the 1980’s and 1990’s, to assess viable methods of acid drainage control. The most significant conclusion of the past 20 years is that it is far easier (economic) to prevent ARD in the first place than to control it. From a number of existing sites where tailings had been placed in lakes in northern Canada, it was concluded that long-term submergence of acidic wastes was probably the most effective means of ARD control. Considerable work has also been done on placement of impervious closure covers over tailings to prevent ingress of air and water. Sophisticated designs of multiple-layer covers, incorporating impervious zones, pervious capillary barriers and topsoil for vegetation growth, have been developed. Covers have been found to present the risk of long term cracking or erosion, and to be ineffective in excluding air, so are less favoured solutions than submergence from the geochemical standpoint. Some of the main technologies for reduction of ARD potential from sulphide bearing tailings are the following:
1. Design for submergence by flooding the tailings at closure. This is a solution, which is being increasingly encouraged and accepted by regulators. However, the authors are concerned that flooded impoundments may create a risky legacy. The more traditional closure configuration for tailings impoundments has been to draw down water ponds as completely as possible, to reduce the potential for dam failure by overtopping or erosion. To raise water levels in impoundments formed by high dams could present considerable long-term risk. One of the reasons that closed tailings impoundments have traditionally proven to be generally more safe, from the physical stability perspective, than operating impoundments is the relatively more “drained” condition of closed impoundments that do not include a large water pond. The flooded closure scenario represents an “undrained” condition that does not allow this improvement in physical stability to develop, so the risk does not decrease with time.
2. Treatment of tailings to create non-acid generating covers. To avoid the necessity of flooding impoundments, non-reactive covers of tailings can be placed on the top of the impoundment on the last few years of operation. It has been shown in several mining operations, for example at the Inco Ontario Division central milling operation in Copper Cliff, Ontario, that by the relatively inexpensive installation of some additional flotation capacity, pyrite can be removed to the level that the tailings can be made non-acid generating. The upper non-acid generating tailings placed on top can be left as a wide beach for dam safety, while the underlying mass of potentially acid generating tailings remains saturated below the long-term water table in the impoundment. Normally, the small amount of pyrite removed by flotation can be disposed as a separate tailings stream, placed in the deepest part of the impoundment where it can be left flooded.
3. Lake or ocean subaqueous disposal. The surest, safest and most cost-effective solution to prevent ARD is sub-aqueous disposal in a lake or the ocean. Tailings will remain permanently submerged and have shown to be non-reactive under water and to have few permanent environmental impacts. The challenge for this solution is that regulators have become reluctant to permit lake or ocean disposal, and there are not always appropriate sites available. In addition, the public often reacts emotionally and negatively to the concept of such disposal, despite the considerable benefits of these approaches. The authors are aware of at least two examples where public pressure incited regulators to demand that existing operations switch from ocean and lake disposal to on-land impoundments, with the result that environmental problems actually increased. The authors do note a slight trend to re-acceptance of subaqueous disposal, particularly in the marine environment, as the true environmental impact of the technique can be demonstrated to be almost negligible in certain instances. Moreover, the corporate risks and environmental liabilities associated with surface tailings storage on many projects grows to the point where project viability is threatened without looking to environmentally acceptable alternatives including subaqueous disposal.
Improved Basic Design Concepts - Improved Upstream Construction.
Considerable attention has been given to improving traditional upstream dam construction to make the technique not only economical but also stable under both static and dynamic conditions. Numerous failures of upstream constructed dams have occurred. The failures have been the results of earthquakes, high saturation levels, steep slopes, poor water control in the pond, poor construction techniques incorporating fines in the dam shell, static liquefaction, and failures of embedded decant structures. Most failures have involved some combination of the above weaknesses.
Based on the above experiences, and through the use of improved analytical tools (computer programs for stability, seepage, and deformation under both static and seismic conditions), safe, optimised designs have been developed. Some of the key design features that have been added include:
• Underdrainage, either as finger drains or blanket drains, to lower the phreatic level in the dam shell; • Beaches compacted to some minimum width to provide a stable dam shell. Beaches are compacted by tracking with bulldozers, which are also used for pushing up berms for support of spigot lines; • Slopes designed to a lower angle than was used for many failed tailings dams. Slopes are generally set at 3 horizontal to 1 vertical or flatter, depending on the other measures incorporated into the designs. Steeper slopes, without an adequate drained and/or compacted beach, create the potential for spontaneous static liquefaction - a phenomenon not widely recognized in 1972 but one responsible for a number of major tailings dam failures.
Improved Basic Design Concepts - Lined Tailings Impoundments.
With the advent of larger gold mining operations, and the almost universal use of sodium cyanide as an essential part of gold extraction, the need came about to develop impervious impoundments to contain cyanide solutions. Although cyanide is in most forms an unstable compound that naturally breaks down on exposure to air, it can be very persistent and migrate long distances in groundwater. As well as cyanided gold tailings, other types of tailings may also be considered potentially contaminating. For protection of aquifers, where tailings impoundments are not sited over impervious soils or bedrock and embankment cut-offs are not sufficient to reduce seepage, it is often necessary to design and construct a liner over the base of a tailings impoundment. Great progress has been made in liner design and construction practise.
Liners may be as simple as selective placement of impervious soil to cover outcrops of pervious bedrock or granular soils, or may need to be a composite liner system constructed over the entire impoundment. Where geomembrane liners are used, it is normal practise to incorporate a drainage layer above the geomembrane, to reduce the pressure head on the liner and minimise leakage through imperfections in the liner. Another benefit of such under-drainage is that a low pore pressure condition is achieved in the tailings, giving them a higher strength than would exist without such under-drainage. The drainage layer typically consists of at least 300 mm of granular material, with perforated pipes at intervals within the drainage layer. The pipes are laid to drain water extracted from the base of the tailings deposit and to discharge to a seepage recovery pond. When a liner extends beneath an impoundment, care must be taken to design for lower foundation shear strength for the downstream slope of the embankment, as the liner may form a plane of weakness.
Improved Basic Design Concepts - Dewatering Technologies.
As shown on the figure below, the basic segregating slurry is part of a continuum of water contents available to the tailings designer in the 21st century. Although tailings dewatering was previously practised for other purposes in the mining process, until recently the only form of tailings for most tailings facilities was a segregating, pumpable slurry with geotechnical water contents of well over 100%.
There are several candidate scenarios where dewatered tailings systems would be of advantage to the mining operation. However, dewatered tailings systems have less application for larger operations for which tailings ponds must serve dual roles as water storage reservoirs, particularly where water balances must be managed to store annual snowmelt runoff to provide water for year round operation.
"Dry" Cake filtered tailings disposal. Development of large capacity, vacuum and pressure belt filter technology has presented the opportunity for disposing tailings in a dewatered state, rather than as a conventional slurry. Tailings can be dewatered to less than 20% moisture content (using soil mechanics convention, in which moisture content is defined as weight of water divided by the dry weight of solids). At these moisture contents, the material can be transported by conveyor or truck, and placed, spread and compacted to form an unsaturated, dense and stable tailings stack (often termed a "dry stack") requiring no dam for retention. While the technology is currently considerably more expensive per tonne of tailings stored than conventional slurry systems, and would be prohibitively expensive for very large tonnage applications, it has particular advantages in the following applications:
• In very arid regions, where water conservation is an important issue. The prime example of such system is at the La Coipa silver/gold operation in the Atacama region of Chile. A daily tailings production of 18,000 t is dewatered by belt filters, conveyed to the tailings site and stacked with a radial, mobile conveyor system. The vacuum filter system was selected for this site because of the need to recover dissolved gold from solution, but is also advantageous for water conservation and also for stability of the tailings deposit in this high seismicity location.
• In very cold regions, where water handling is very difficult in winter. A dewatered tailings system, using truck transport, is in operation at Falconbridge’s Raglan nickel operation in the arctic region of northern Quebec. The system is also intended to provide a solution for potential acid generation, as the tailings stack will become permanently frozen. A dry stack tailings system is also being planned for a new gold project in central Alaska.
• Relatively low tonnage operations. A separate tailings impoundment can be avoided all together by having a tailings/waste rock co-disposal facility.
• Regions where a “dry landscape” upon closure is required. The tailings area can be developed and managed more like a waste dump and therefore avoids many of the operation and closure challenges of a conventional impoundment.
Moreover, filtered tailings stacks have regulatory attraction, require a smaller footprint for tailings storage (much lower bulking factor), are easier to reclaim and close, and have much lower long-term liability in terms of structural integrity and potential environmental impact.
Coal mining is the extraction or removing of coal from the earth for use as fuel. A coal mine and its accompanying structures are collectively known as a colliery. For the world history see History of coal mining.
..... Click the link for more information.
Tailings represent external costs of mining. 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. Yesterday's tails can be tomorrow's resource, as seen during the 1990s when the extensive tailings dumps of Kalgoorlie / Boulder in Western Australia were re-processed profitably by KalTails Mining.
In coal and oil sands mining, the word '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 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 quantities of heavy metals found in the host ore, and they may contain added chemicals used in the extraction process. Elements are rarely in elemental form, more often as complex compounds.
Common minerals and elements found in Tailings
- Arsenic - Found in association with gold ores
- Barite
- Calcite
- Fluorite
- Radioactive materials - Naturally present in many ores
- Mercury
- Sulfur - Forms many sulfide compounds / pyrites
- Cadmium
- Hydrocarbons - Introduced by mining and processing equipment (oils & greases)
- Cyanide - as both Sodium Cyanide (NaCN) and Hydrogen Cyanide (HCN). Leaching agent.
- SEX - Sodium Ethyl Xanthate. Floatation agent.
- PAX - Potassium Amyl Xanthate. Floatation agent.
- MIBC - Methyl Isobutyl Carbinol. Frothing agent.
- Sulfamic acid - Cleaning / descaling agent.
- Sulfuric acid - Used in large quantities in the PAL process (Pressure Acid Leaching).
- Activated Carbon - Used in CIP (Carbon In Pulp) and CIL (Carbon In Leach) processes.
- Calcium - Different compounds, introduced as Lime to aid in pH control.
Environmental and Social Considerations
Tailings in general, are often pointed at by environmentally active groups as evidence of the destruction that mining operations can wreak upon the planet. And to a degree, they have a valid point. In the past, non-environmentally friendly methods were the method of the day - profit at all costs being the main motivator. In todays modern mining environment, it is possible to find many mining operators continuing to engage in tailings disposal methods that are not environmentally friendly, particularly in developing nations where legislative requirements are far less than first world countries, and the need for quick cash overrules any environmental considerations.There is, however, a strong push from the leading mining houses and their design consultants to support the cessation of unsustainable tailings disposal practises. Unsustainable, in the sense that continuing to blatantly pollute the local environment damages a mining company's social license to operate, and by default damages the social licenses of all mining companies. It is in the mining industry's best interests to support efforts to prevent and halt non-sustainable tailings disposal methods.
Reprocessing of old tailings dumps and dams has assisted in the cleaning up of legacy tailings dumps, with the reproccessed tailings being disposed of using a more effective method than a simple surface dump.
Tailings Disposal Methods
Pond Storage
There are many different subsets of this method. Large earthen dams may be constructed and then filled with the tailings. Tailings may be deposited into natural geographical depressions. 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.Disposal into 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 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 recently at the Beaconsfield Mine DisasterDisposal into river systems
Usually called RTD - Rivering Tailings Disposal. Not a particularly environmentally sound practise, it has seen significant utilisation in the past, leading to such spectacular environmental damage as done by the Mt Lyell Mining Company in Tasmania to the King River. It is still practised at some operations in the world, and while experts agree it is a feasible method for locations where the river is rapidly flowing and turbulent and the additional silt loading will not impact on the river quality, it is not generally favored and is seeing a gradual decline in use.Disposal into the oceans
Commonly referred to as STD (Submarine Tailings Disposal) or DSTD (Deep Sea Tailings Disposal). If a mine is located in close proximity to the coast, and the coast itself is not an excessive distance from a continental shelf, STD is conceptually an excellent method for the disposal of tailings. Tailings can be conveyed using a pipeline then discharged so as to eventually descend into the depths. Practially, 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 Bismark Sea by Nautilus Minerals proposes to use a modified STD method back down to depths below 1500 metres. Many countries specifically outlaw the use of STD methods.New Developments
A number of improvements have been made in tailings disposal technology and tailings dam design, both to improve on the weaknesses of previous practices and also to take advantage of tailings processing technologies. Geochemical aspects now largely drive the siting, of a tailings impoundment, the design of retention structures, and tailings disposal technology. There have been technologies put forward as panaceas for tailings disposal problems, which have turned out to be flawed in practice. These improvements can be categorized as changes in basic management practices and changes in tailings characteristics through pre-discharge dewatering.Designing for Geochemical Issues
Geochemical issues have become highly prominent as severe acid generation problems became apparent at a number of mature mines around the world. Some of these mines, which had been operated by smaller mining companies, became orphan sites, leaving significant legacies for future generations. The majority of the acid drainage mine sites have become very expensive legacies for the major mining companies that owned them. It has been necessary to develop and operate acid drainage collection and treatment systems for continued operation and closure of numerous mines. Capital costs for ARD collection and treatment systems have been in the several tens of millions of dollars, with ongoing operating costs up to several millions of dollars annually. As a result, companies developing new mines have focussed on methods to predict and prevent or reduce acid generation from tailings.
Considerable research, for example CANMET's Mine Effluent Neutral Drainage (MEND) program, was carried out in the 1980’s and 1990’s, to assess viable methods of acid drainage control. The most significant conclusion of the past 20 years is that it is far easier (economic) to prevent ARD in the first place than to control it. From a number of existing sites where tailings had been placed in lakes in northern Canada, it was concluded that long-term submergence of acidic wastes was probably the most effective means of ARD control. Considerable work has also been done on placement of impervious closure covers over tailings to prevent ingress of air and water. Sophisticated designs of multiple-layer covers, incorporating impervious zones, pervious capillary barriers and topsoil for vegetation growth, have been developed. Covers have been found to present the risk of long term cracking or erosion, and to be ineffective in excluding air, so are less favoured solutions than submergence from the geochemical standpoint. Some of the main technologies for reduction of ARD potential from sulphide bearing tailings are the following:
1. Design for submergence by flooding the tailings at closure. This is a solution, which is being increasingly encouraged and accepted by regulators. However, the authors are concerned that flooded impoundments may create a risky legacy. The more traditional closure configuration for tailings impoundments has been to draw down water ponds as completely as possible, to reduce the potential for dam failure by overtopping or erosion. To raise water levels in impoundments formed by high dams could present considerable long-term risk. One of the reasons that closed tailings impoundments have traditionally proven to be generally more safe, from the physical stability perspective, than operating impoundments is the relatively more “drained” condition of closed impoundments that do not include a large water pond. The flooded closure scenario represents an “undrained” condition that does not allow this improvement in physical stability to develop, so the risk does not decrease with time.
2. Treatment of tailings to create non-acid generating covers. To avoid the necessity of flooding impoundments, non-reactive covers of tailings can be placed on the top of the impoundment on the last few years of operation. It has been shown in several mining operations, for example at the Inco Ontario Division central milling operation in Copper Cliff, Ontario, that by the relatively inexpensive installation of some additional flotation capacity, pyrite can be removed to the level that the tailings can be made non-acid generating. The upper non-acid generating tailings placed on top can be left as a wide beach for dam safety, while the underlying mass of potentially acid generating tailings remains saturated below the long-term water table in the impoundment. Normally, the small amount of pyrite removed by flotation can be disposed as a separate tailings stream, placed in the deepest part of the impoundment where it can be left flooded.
3. Lake or ocean subaqueous disposal. The surest, safest and most cost-effective solution to prevent ARD is sub-aqueous disposal in a lake or the ocean. Tailings will remain permanently submerged and have shown to be non-reactive under water and to have few permanent environmental impacts. The challenge for this solution is that regulators have become reluctant to permit lake or ocean disposal, and there are not always appropriate sites available. In addition, the public often reacts emotionally and negatively to the concept of such disposal, despite the considerable benefits of these approaches. The authors are aware of at least two examples where public pressure incited regulators to demand that existing operations switch from ocean and lake disposal to on-land impoundments, with the result that environmental problems actually increased. The authors do note a slight trend to re-acceptance of subaqueous disposal, particularly in the marine environment, as the true environmental impact of the technique can be demonstrated to be almost negligible in certain instances. Moreover, the corporate risks and environmental liabilities associated with surface tailings storage on many projects grows to the point where project viability is threatened without looking to environmentally acceptable alternatives including subaqueous disposal.
Improved Basic Design Concepts - Improved Upstream Construction.
Considerable attention has been given to improving traditional upstream dam construction to make the technique not only economical but also stable under both static and dynamic conditions. Numerous failures of upstream constructed dams have occurred. The failures have been the results of earthquakes, high saturation levels, steep slopes, poor water control in the pond, poor construction techniques incorporating fines in the dam shell, static liquefaction, and failures of embedded decant structures. Most failures have involved some combination of the above weaknesses.
Based on the above experiences, and through the use of improved analytical tools (computer programs for stability, seepage, and deformation under both static and seismic conditions), safe, optimised designs have been developed. Some of the key design features that have been added include:
• Underdrainage, either as finger drains or blanket drains, to lower the phreatic level in the dam shell; • Beaches compacted to some minimum width to provide a stable dam shell. Beaches are compacted by tracking with bulldozers, which are also used for pushing up berms for support of spigot lines; • Slopes designed to a lower angle than was used for many failed tailings dams. Slopes are generally set at 3 horizontal to 1 vertical or flatter, depending on the other measures incorporated into the designs. Steeper slopes, without an adequate drained and/or compacted beach, create the potential for spontaneous static liquefaction - a phenomenon not widely recognized in 1972 but one responsible for a number of major tailings dam failures.
Improved Basic Design Concepts - Lined Tailings Impoundments.
With the advent of larger gold mining operations, and the almost universal use of sodium cyanide as an essential part of gold extraction, the need came about to develop impervious impoundments to contain cyanide solutions. Although cyanide is in most forms an unstable compound that naturally breaks down on exposure to air, it can be very persistent and migrate long distances in groundwater. As well as cyanided gold tailings, other types of tailings may also be considered potentially contaminating. For protection of aquifers, where tailings impoundments are not sited over impervious soils or bedrock and embankment cut-offs are not sufficient to reduce seepage, it is often necessary to design and construct a liner over the base of a tailings impoundment. Great progress has been made in liner design and construction practise.
Liners may be as simple as selective placement of impervious soil to cover outcrops of pervious bedrock or granular soils, or may need to be a composite liner system constructed over the entire impoundment. Where geomembrane liners are used, it is normal practise to incorporate a drainage layer above the geomembrane, to reduce the pressure head on the liner and minimise leakage through imperfections in the liner. Another benefit of such under-drainage is that a low pore pressure condition is achieved in the tailings, giving them a higher strength than would exist without such under-drainage. The drainage layer typically consists of at least 300 mm of granular material, with perforated pipes at intervals within the drainage layer. The pipes are laid to drain water extracted from the base of the tailings deposit and to discharge to a seepage recovery pond. When a liner extends beneath an impoundment, care must be taken to design for lower foundation shear strength for the downstream slope of the embankment, as the liner may form a plane of weakness.
Improved Basic Design Concepts - Dewatering Technologies.
As shown on the figure below, the basic segregating slurry is part of a continuum of water contents available to the tailings designer in the 21st century. Although tailings dewatering was previously practised for other purposes in the mining process, until recently the only form of tailings for most tailings facilities was a segregating, pumpable slurry with geotechnical water contents of well over 100%.
There are several candidate scenarios where dewatered tailings systems would be of advantage to the mining operation. However, dewatered tailings systems have less application for larger operations for which tailings ponds must serve dual roles as water storage reservoirs, particularly where water balances must be managed to store annual snowmelt runoff to provide water for year round operation.
"Dry" Cake filtered tailings disposal. Development of large capacity, vacuum and pressure belt filter technology has presented the opportunity for disposing tailings in a dewatered state, rather than as a conventional slurry. Tailings can be dewatered to less than 20% moisture content (using soil mechanics convention, in which moisture content is defined as weight of water divided by the dry weight of solids). At these moisture contents, the material can be transported by conveyor or truck, and placed, spread and compacted to form an unsaturated, dense and stable tailings stack (often termed a "dry stack") requiring no dam for retention. While the technology is currently considerably more expensive per tonne of tailings stored than conventional slurry systems, and would be prohibitively expensive for very large tonnage applications, it has particular advantages in the following applications:
• In very arid regions, where water conservation is an important issue. The prime example of such system is at the La Coipa silver/gold operation in the Atacama region of Chile. A daily tailings production of 18,000 t is dewatered by belt filters, conveyed to the tailings site and stacked with a radial, mobile conveyor system. The vacuum filter system was selected for this site because of the need to recover dissolved gold from solution, but is also advantageous for water conservation and also for stability of the tailings deposit in this high seismicity location.
• In very cold regions, where water handling is very difficult in winter. A dewatered tailings system, using truck transport, is in operation at Falconbridge’s Raglan nickel operation in the arctic region of northern Quebec. The system is also intended to provide a solution for potential acid generation, as the tailings stack will become permanently frozen. A dry stack tailings system is also being planned for a new gold project in central Alaska.
• Relatively low tonnage operations. A separate tailings impoundment can be avoided all together by having a tailings/waste rock co-disposal facility.
• Regions where a “dry landscape” upon closure is required. The tailings area can be developed and managed more like a waste dump and therefore avoids many of the operation and closure challenges of a conventional impoundment.
Moreover, filtered tailings stacks have regulatory attraction, require a smaller footprint for tailings storage (much lower bulking factor), are easier to reclaim and close, and have much lower long-term liability in terms of structural integrity and potential environmental impact.
External links
- Uranium tailings
- Tailings Info site
- Extox.net
- Submarine Tailings Disposal at the Mineral Policy Institute
Footnotes
1. ^ Baumgart, Don. Pressure Builds to End Hydraulic Gold Mining. California Gold Rush Stories. Nevada County Gold. Retrieved on 2006-05-10.
2. ^ Golden Gamble in Grass Valley. YubaNet.com. Retrieved on 2006-05-14.
2. ^ Golden Gamble in Grass Valley. YubaNet.com. Retrieved on 2006-05-14.
ore is a volume of rock containing components or minerals in a mode of occurrence that renders it valuable for mining. An ore must contain materials that are
..... Click the link for more information.
- valuable
- in concentrations that can be profitably mined, transported, milled, and processed.
..... Click the link for more information.
In economics, an externality is an impact (positive or negative) on anyone not party to a given economic transaction.
An externality occurs when a decision causes costs or benefits to third party stakeholders, often, although not necessarily, from the use of a public good.
..... Click the link for more information.
An externality occurs when a decision causes costs or benefits to third party stakeholders, often, although not necessarily, from the use of a public good.
..... Click the link for more information.
worldwide view.
Coal mining is the extraction or removing of coal from the earth for use as fuel. A coal mine and its accompanying structures are collectively known as a colliery. For the world history see History of coal mining.
..... Click the link for more information.
Tar sands is a common name of what are more properly called bituminous sands, but also commonly referred to as oil sands or (in Venezuela) extra-heavy oil. They are a mixture of sand or clay, water, and extremely heavy crude oil.
..... Click the link for more information.
..... Click the link for more information.
Heap leaching is an industrial mining process to extract precious metals and copper compounds from ore.
..... Click the link for more information.
Process
The mined ore is crushed into small chunks and heaped on an impermeable plastic and/or clay lined leach pad where it can be irrigated with a leach solution to..... Click the link for more information.
3, 5
(mildly acidic oxide)
Electronegativity 2.18 (scale Pauling)
Ionization energies
(more) 1st: 947.0 kJmol−1
2nd: 1798 kJmol−1
3rd: 2735 kJmol−1
..... Click the link for more information.
(mildly acidic oxide)
Electronegativity 2.18 (scale Pauling)
Ionization energies
(more) 1st: 947.0 kJmol−1
2nd: 1798 kJmol−1
3rd: 2735 kJmol−1
..... Click the link for more information.
Barite (BaSO4) is a mineral consisting of barium sulfate. It is generally white or colorless, and is the main source of barium. Baryte is the British spelling, and the mineral is also called heavy spar.
..... Click the link for more information.
..... Click the link for more information.
calcite]] The carbonate mineral, calcite, is a chemical or biochemical calcium carbonate corresponding to the formula CaCO3 and is one of the most widely distributed minerals on the Earth's surface.
..... Click the link for more information.
..... Click the link for more information.
Fluorite (also called fluorspar) is a 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.
..... Click the link for more information.
..... Click the link for more information.
Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. This decay, or loss of energy, results in an atom of one type, called the parent nuclide
..... Click the link for more information.
..... Click the link for more information.
2, 1
(mildly basic oxide)
Electronegativity 2.00 (scale Pauling)
Ionization energies 1st: 1007.1 kJ/mol
2nd: 1810 kJ/mol
3rd: 3300 kJ/mol
Atomic radius 150 pm
Atomic radius (calc.
..... Click the link for more information.
(mildly basic oxide)
Electronegativity 2.00 (scale Pauling)
Ionization energies 1st: 1007.1 kJ/mol
2nd: 1810 kJ/mol
3rd: 3300 kJ/mol
Atomic radius 150 pm
Atomic radius (calc.
..... Click the link for more information.
6
(strongly acidic oxide)
Electronegativity 2.58 (Pauling scale)
Ionization energies
(more) 1st: 999.6 kJmol−1
2nd: 2252 kJmol−1
3rd: 3357 kJmol−1
Atomic radius 100 pm
Atomic radius (calc.
..... Click the link for more information.
(strongly acidic oxide)
Electronegativity 2.58 (Pauling scale)
Ionization energies
(more) 1st: 999.6 kJmol−1
2nd: 2252 kJmol−1
3rd: 3357 kJmol−1
Atomic radius 100 pm
Atomic radius (calc.
..... Click the link for more information.
Cadmium (IPA: /ˈkædmiəm/) is a chemical element in the periodic table that has the symbol Cd and atomic number 48.
..... Click the link for more information.
..... Click the link for more information.
hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. With relation to chemical terminology, aromatic hydrocarbons or arenes, alkanes, alkenes and alkyne-based compounds composed entirely of carbon or hydrogen are referred to as "Pure" hydrocarbons, whereas
..... Click the link for more information.
..... Click the link for more information.
cyanide ion, CN−.
From the top:
1. Valence-bond structure
2. Space-filling model
3. Electrostatic potential surface
4. 'Carbon lone pair' HOMO]] A cyanide
..... Click the link for more information.
From the top:
1. Valence-bond structure
2. Space-filling model
3. Electrostatic potential surface
4. 'Carbon lone pair' HOMO]] A cyanide
..... Click the link for more information.
Xanthates are the salts and esters of a xanthic acid, ROC(=S)SH or O-esters of dithiocarbonic acid where R is any organic residue. The ethyl ester CH3CH2OC(=S)SH is also the parent compound xanthic acid
..... Click the link for more information.
..... Click the link for more information.
Sulfamic acid, also known as amidosulfonic acid, amidosulfuric acid, aminosulfonic acid, and sulfamidic acid, is a molecular compound with the formula H3NSO3. This colorless, water-soluble compound finds many applications.
..... Click the link for more information.
..... Click the link for more information.
Sulfuric (or sulphuric) acid, H2SO4, is a strong mineral acid. It is soluble in water at all concentrations. It was once known as oil of vitriol, coined by the 8th-century Arabian alchemist Jabir ibn Hayyan (Geber) after his discovery of the chemical.
..... Click the link for more information.
..... Click the link for more information.
PAL, short for Phase Alternating Line, is a colour encoding system used in broadcast television systems in large parts of the world. Other common analogue television systems are SECAM and NTSC.
..... Click the link for more information.
..... Click the link for more information.
Activated carbon, also called activated charcoal or activated coal, is a general term which covers carbon material mostly derived from charcoal. For all three variations of the name, "activated" is sometimes substituted by "active".
..... Click the link for more information.
..... Click the link for more information.
Carbon in Pulp (CIP) is a technique for recovery of gold which has been liberated into a cyanide solution as part of the gold cyanidation process, a gold extraction technique.
Introduced in 1985, Carbon in Pulp is regarded as a simple and cheap process.
..... Click the link for more information.
Introduced in 1985, Carbon in Pulp is regarded as a simple and cheap process.
..... Click the link for more information.
Calcium (IPA: /ˈkalsiəm/) is the chemical element in the periodic table that has the symbol Ca and atomic number 20. It has an atomic mass of 40.078.
..... Click the link for more information.
..... Click the link for more information.
Lime may refer to:
..... Click the link for more information.
- Lime (fruit), various green to yellow citrus fruits
- Lime (color), various colors of green
- Lime (mineral), a group of calcium compounds and minerals in which they predominate
..... Click the link for more information.
Stopes may refer to:
..... Click the link for more information.
- Marie Stopes (1880-1958), Scottish author
- Stopes, rooms supported by surrounding pillars of standing rock in Hard rock mining
Also see
- Stull Stoping, an underground mining method
..... Click the link for more information.
The Beaconsfield mine collapse occurred on April 25 2006 in Beaconsfield, Tasmania, Australia. Of the 17 people who were in the mine at the time, 14 escaped immediately following the collapse, one was killed, and the remaining two were found alive after five days.
..... Click the link for more information.
..... Click the link for more information.
The Mineral Policy Institute "is an Australian-based non-government organisation specialising in advocacy, campaigning and research to prevent environmentally and socially destructive mining, minerals and energy projects in Australia, Asia and the Pacific".
..... Click the link for more information.
..... Click the link for more information.
This article is copied from an article on Wikipedia.org - the free encyclopedia created and edited by online user community. The text was not checked or edited by anyone on our staff. Although the vast majority of the wikipedia encyclopedia articles provide accurate and timely information please do not assume the accuracy of any particular article. This article is distributed under the terms of GNU Free Documentation License.
Herod_Archelaus
