How are waste materials managed at mine site????
The type, amount, and properties of mine waste produced at different mines vary depending on the resource being mined, process technology used, and geology at the mine site. While many mine wastes are benign, mining companies manage their waste in order to deal with the large volumes of waste produced and to prevent the release of contaminates into the environment. Waste management plans are developed as part of the mine approval process in Canada, and consist of waste storage area selection and design, strategies to address problematic waste, and longterm stabilization of waste as part of mine closure. Origins of waste at mine sites
Like the maority of human activities, mining operations produce waste materials. !Waste" is a general term for material which currently has little or no economic value. #$% The soil and rock which is removed to gain access to buried ore, and the material &water, solids, and gases' left behind after the ore has been processed to remove the valuable commodities, are considered to be waste materials. (owever, the difference in mineral content between ore and waste rock can change depending on market conditions and available e)traction technology, and there are a number of cases where material that was once considered waste has become a resource for modern mining operations. #*% Types Ty pes of mine waste
There are different types of mine waste materials which vary in their physical and chemical composition, their potential for environmental
contamination, and how they are managed at mine sites. Types of mine waste include+ #*% •
Overburden: verburden includes the soil and rock that is
removed to gain access to the ore deposits at open pit mines. t is usually piled on the surface at mine sites where it will not impede further e)pansion of the mining operation moving large volumes of material is e)pensive. verburden generally has a low potential for environmental contamination, and is often used at mine sites for landscape contouring and revegetation during mine closure. •
Waste rock: Waste rock is material that contains minerals in
concentrations considered too low to be e)tracted at a profit. Waste rock is often stored in heaps or dumps on the mine site, but may be stored underwater with tailings if it contains a lot of sulphide minerals and has a high potential for acid rock drainage formation. Waste rock dumps are generally covered
with soil and revegetated following mine closure, although there are cases of waste rock being re-mined due to an increase in mineral market prices or improvements in e)traction technology. •
Tailings: Tailings are finely ground rock and mineral waste
products of mineral processing operations. Tailings can also contain leftover processing chemicals, and are usually deposited in the form of a water-based slurry into tailings ponds &sedimentation lagoons enclosed by dams built to capture and store the tailings', although offshore tailings disposal has been
successful in some cases. Tailings dams are discussed in further detail below. •
Slags: Slags are non-metallic by-products from metal smelting,
and were historically considered to be waste. /lags are largely environmentally benign, and are being used increasingly as aggregate in concrete and road construction. •
Mine water: 0ine water is produced in a number of ways at
mine sites, and can vary in its quality and potential for environmental contamination. Water at mine sites is fre1uently monitored and various water management strategies have been developed to reduce the amount of mine
water produced, and treat the water before it is discharged to the environment. •
Water treatment sludge: /ludge is produced at active water treatment plants used at some mine sites, and consists of the
solids that had been removed from the water as well as any chemicals that had been added to improve the efficiency of the process. 2lthough ways of recycling the sludge are being e)plored, the maority of sludge has little economic value and is handled as waste. 3isposal of water treatment residues in underground mine workings is the least e)pensive option where it is permitted and environmentally safe. n e)treme cases where the sludge is rich in cadmium or arsenic, it may be classified as hazardous waste and re1uire special handling and disposal. #4% •
aseous wastes: 5aseous wastes include particulate matter
&dust' and sulphur o)ides &/)'. The maority of emissions to the atmosphere are produced during high-temperature chemical
processing such as smelting, and vary in their composition and potential for environmental contamination. 6nvironmental control technologies such as gravity collectors, cyclones, and electrostatic precipitators are capable of removing up to 77.89 of dust and fumes, and wet scrubbers typically remove :;-7<9 of sulphur o)ide emissions. #=, <% n Canada, the atmospheric sulphur dio)ide emissions from metal smelters have decreased by 489 between *;;4 and *;$;. #>% !nvironmental impacts of mine waste
The environmental impact of mine waste depends on its type and composition, which vary considerably with the commodity being mined, type of ore, and technologies used to process the ore. #*% ?or instance, where waste rock and tailings contain significant 1uantities of sulphide minerals and are e)posed to air and water, acid rock drainage &2@3' can occur. #8% 2s a result, every mine re1uires its own waste characterization, prediction, monitoring, control, and treatment. #:% 0any mine wastes are environmentally benign, and can be used for landform reconstruction, vegetation covers, and road and dam construction. #:% The maor environmental impacts from waste disposal at mine sites can be divided into two categories+ the loss of productive land following its conversion to a waste storage area, and the introduction of sediment, acidity, and other contaminates into surrounding surface and groundwater from water running over e)posed problematic or chemically reactive wastes. #*, :%
Management of mine wastes
0ine wastes re1uire careful management to ensure the long-term stability of storage and disposal facilities, and to prevent and minimize air, water, and soil contamination. #*% The inappropriate or unsafe management of wastes at mining operations continues to generate opposition from local communities, the general public, and non-government organizations, and has contributed to the negative public perception of the mining industry. #*% Technological advances and changes in regulations have resulted in significant changes in waste management practices over the last $; to *; years, and mine wastes at modern mines are generally better managed than they have been in the past. #7, $;% Waste management plans are fre1uently developed before a mine is constructed, and the reclamation of waste rock dumps and tailings ponds are increasingly incorporated into the designs of new mines. #$, 7% n addition, in many parts of the world authorities re1uire a proper waste management plan before they will issue a mining permit. #8% 0ine waste management practices and storage facilities used at different mines are based on common design principles, but are optimized by mine engineers depending on specific site conditions. #7% These designs take into account the potential for e)treme events, such as earth1uakes and floods. #$$% 5uidelines on waste management and mine closure have been developed at international, national, and regional levels, and provide an advisory framework for best practices in mine waste management. #7% The usual approach to managing wastes is to contain and collect them at the point of production, treat the wastes to make them environmentally safe if necessary, and dispose of them to the land, water, or air. #*% The waste
management method used at a particular mine depends mainly on an evaluation of cost, environmental performance, and risk of failure. #$*% /uccessful management of tailings and waste rock is based on selecting appropriate waste storage locations, and proper material characterization, including the accurate prediction of long-term chemical behaviour. #$*% /olid mine waste &overburden, waste rock, solidified tailings, slag, dust' can be used as backfill in underground or open pit workings, stored in piles on site or underwater to prevent 2@3 from occurring in the case of problematic wastes, used in construction of roads and dams at the mine, or recycled. #$% Water can be recycled and reused for dust suppression and mineral processing, or treated and discharged into the environment. #$;% Tailings management
Aecause tailings are composed of fine particles &sand, silt, and clay-sized material', and often have a high water content, they have been particularly troublesome to manage. n the past, tailings were deposited directly into rivers or wetlands, which would introduce sediment and contaminates into those water bodies and in many cases adversely affect a1uatic life. #$% Tailings are currently used as backfill in underground mines, stored in open pits, dried and stacked, or pumped into tailings ponds on site. #$% 2lthough there have been a number of incidents where the dams securing tailings ponds have been breached, mining engineers have been learning from the en1uiries into tailing dam failures, and have improved tailings dam design and e)ecution. 2 compilation of worldwide tailings dam failure statistics between $7;7 and $777 shows an improving trend as mining companies have learned from past mistakes and as regulators have imposed more stringent regulations and conducted more inspections. #8% n
the $78;s, there were == tailings dam failures, in the $7:;s, *8 failures, and in the $77;s, only 8 failures. #8% 0odern tailings dam design is very technical, and takes a number of site-specific factors into consideration, such as rainfall and flooding predictions, earth1uake response, seepage control, tailings discharge method and rate, and changes over the lifetime of the dams. #8% Bon-critical structures are typically designed to withstand a $-in-$;;-year flood, while more critical structures are designed for a $-in$;;;-year event or above. #$4% n response to concerns over tailings dam failures and water contamination, some mines are opting to produce thickened tailings,
which are pressed or have chemicals added to remove e)cess water. #*% Thickened tailings can be mi)ed with cement and used in construction or as backfill in underground mines. #$% 2lthough producing thickened tailings is often more e)pensive than storing the tailings in a pond, the use of thickened tailings is increasing, especially in arid areas where water availability is an issue. #*% Turning mine wastes into a resource
The large volumes of waste produced at mining operations are e)pensive to manage, and are fre1uently cited as an obstacle in the environmental sustainability of mining. The mining industry plays a leading role in waste management, and is one of few industries that recycles its own waste. #:% ses of mine waste include+ #$; p. =;>% •
Waste rock: Can be reprocessed to e)tract minerals and metals,
used as backfill, landscaping material, aggregate in road construction, or feedstock for cement and concrete
•
Manganese tailings: 0anganese tailings have been used in
agro-forestry, buildings and construction materials, coatings, resin, glass, and glazes •
"lay#ric$ tailings: Clay-rich tailings have been used for making
bricks, floor tiles, and cement •
Slag: /lag is often used for road construction, and in concrete
and cement •
%ed mud: Aau)ite red mud is solid alkaline waste produced in
aluminium refineries. @ed mud has been used as a soil amender, in waste water treatment, and as a raw material for glass, ceramics, and bricks •
Mine water: 0ine water is used for dust suppression and mineral
processing, industrial and agricultural uses, as a coolant, and as a source of drinking water •
Water treatment sludge: /ludge from 2@3 treatment, which is
high in iron, has been sold commercially for use in pigments •
Sulp$ur o&ide emissions: 0any smelters have installed acid
plants to convert sulphur dio)ide to sulphuric acid, a useful industrial chemical #=% Management of waste following mine closure
3espite the recycling and reuse of many wastes at mine sites, the maority of waste produced is still placed into storage facilities, and the reclamation and long-term management of these facilities has become an important part of modern mine development and mine closure. #$;% @egulators may re1uire any waste storage structures to remain stable for a minimum of $;; to *;; years, which means they must withstand e)treme
events such as floods and earth1uakes. #$$% 0ine closure activities often involve containing and covering tailings to prevent their escape into the environmentD minimizing the amount of water seeping from the tailings into surface or groundwaterD covering waste rock piles and e)posed materials with topsoil and planting vegetation to prevent erosionD and designing the final land formation to minimize erosion and post-closure maintenance. #*% Elans for mine closure and site cleanup are re1uired as part of the mine permitting process in Canada and these plans are updated after additional study #$7%. t is also common in Canada for government agencies to issue a new permit on shutdown to cover mine closure. #$7%
"ase Study: Myra 'alls Mine( "ampbell %iver( )ancouver *sland( +,", Myra 'alls Mine is a zinc, copper, lead, gold, and silver mine located at the
south end of Autte Lake in the /trathcona-Westmin Erovincial Eark, :; kilometers southwest of Campbell @iver on Fancouver sland, Aritish Columbia. #$=% 0yra ?alls 0ine is owned by the Aelgian mining company Bystar after it ac1uired Areakwater @esources, the mineGs previous owners, in 2pril *;$$. #$<% The mine began as an open pit in $7>>, but now active mining is only taking place underground over more than *=; kilometers of tunnels and shafts. #$=% re is blasted and crushed underground before being hoisted to the mill on the surface. #$=% Water is added and the ore is ground up to sand-sized particlesD froth floatation cells are then used to separate the metal concentrates from the resulting slurry, and the tailings are piped to a
tailings pond behind a man-made dam. #$=% 2bout half the tailings &the coarser fraction' settle out of the slurry, and are removed, mi)ed with cement, and piped back down to the mine as a paste which is used to back-fill the mine workings. #$=% The underground mine does not have a waste rock dump because so little waste rock is mined and brought to the surface. #$=% 0uch of the water coming from or flowing over the mine site becomes contaminated with dissolved metals including aluminum, zinc, copper, and iron as a result of acid rock drainage &2@3'. #$>% n the late $78;s, it was discovered that the concentration of zinc in Autte Lake was increasing as a result of inflows of mine water. #$>% 2 number of water control and treatment facilities were installed in the $7:;s, which were very
successful in reducing levels of contamination coming from the mine. #$>% 2ll the water from the mine, mill, and tailings pond is collected in si) polishing ponds, and lime is added to raise the p( and remove the metals. #$=% The resulting sludge is pumped to the tailings pond for storage. #$=% 0ost of the water used in the mill is pumped back and re-used, and the water is tested daily to make sure it meets regulatory re1uirements. #$=% 0yra ?alls is the only mine in A.C. located within a Erovincial Eark. #$=% The /trathcona-Westmin Erovincial Eark is a Class A park, which means certain activities &commercial logging, hydroelectric development, or mining' may be permitted, where they would not be in a Class 2 park. #$8, $:% 2n area of 4,4*: hectares was separated out of the /trathcona Class 2 Eark in $7>< and given special designation because of value of the minerals found in the area and the decision by the provincial government to allow e)ploration and mining. #$=% While the mine controls 4> s1uare
kilometers &4,>;; hectares' it only has surface footprint of $.8 s1uare kilometers &$8; hectares'. #$=% The obective of the 0yra ?alls mine closure plan is to reclaim the land to a Class 2 park. #$=%
The current reclamation plan calls for the waste rock from the original pit mine to be used to backfill the open pit, and a cover system will prevent further 2@3 formation at the ponds and old waste dumps. #$=% Trials of different materials that will form the cover system are being conducted, and the best material so far has been made with a mi)ture of mine tailings and sludge from the polishing ponds. #$=% @evegetation and landscaping were undertaken around the mine site following the completion of construction activities in $7:<, disused roads and facilities have been decommissioned and removed, and plots were set up to identify the types of plants which would be best suited for revegetation of the mine site. #$>% /o far C2H * million has been spent on reclamation, and another C2H $; million dollars has been set aside for future work. #$=% The total reclamation cost is e)pected to be C2H *$.$ million. #$=% - /ee more at+ http+IIwww.miningfacts.orgI6nvironmentI(ow-are-wastematerials-managed-at-mine-sitesIJsthash.B@)TKv=(.dpuf
