Underground mining
The extraction of ore from beneath the surface of the ground. Underground mining is also applied to deposits of industrial (nonmetallic) minerals and rocks, and underground or deep methods are used in coal mining. Some ores and industrial minerals can be recovered from beneath the ground surface by solution mining or in-place leaching using boreholes. See also: Coal mining; Solution mining
Underground mining involves a larger capital investment and higher production cost per ton of ore than open pit mining. It is done where mineral deposits are situated beyond the economic depth of open pit mining; it is generally applied to steeply dipping or thin deposits and to disseminated or massive deposits for which the cost of removing the overburden and the maintaining of a slope angle in adjacent waste rock would be prohibitive. In some situations, the shallower portion of a large orebody will be mined by open pit methods, and the deeper portion will be mined by underground methods. See also: Open-pit mining
Underground mine entries are by shaft, adit, incline, or spiral ramp (Fig. 1). Development workings, passageways for gaining access to the orebody from stations on individual mine levels, are called drifts if they follow the trend of the mineralization, and cross-cuts if they are driven across the mineralization. Workings on successive mine levels are connected by raises, passageways that are driven upward. Winzes are passageways that are sunk downward, generally from a lowermost mine level.
Fig. 1 Underground mining entries and workings.
In a fully developed mine with a network of levels, sublevels, and raises for access, haulage, pumping, and ventilation, the ore is mined from excavations referred to as stopes. Pillars of unmined material are left between stopes and other workings for temporary or permanent natural support. In large-scale mining methods and in methods where an orebody and its overlying waste rock are allowed to break and cave under their own weight, the ore is extracted in large collective units called blocks, panels, or slices. See also: Mining
ادامه مطلب
introduction
Dams are structural barriers built to obstruct or control the flow of water in rivers and streams. They are designed to serve two broad functions. The first is the storage of water to compensate for fluctuations in river discharge (flow) or in demand for water and energy. The second is the increase of hydraulic head, or the difference in height between water levels in the lake created upstream of the dam and the downstream river
ادامه مطلب
◄ دراگلين(drag line):
وسيله اي است که براي خاکبرداري و حفر مواد نرم در قسمتهاي گود به کار ميرود. شکل عمومي اين دستگاه نيز شبيه بيل مکانيکي اما صندوقه اين دستگاه به دو رشته کابل متصل است که به وسيله اين کابل ها ميتوان آن را در قسمتهاي مختلف به کار برد.به طور مختصر شيوه کار اين دستگاه به اين صورت است که ابتدا کابلها را رها ميکنند و صندوقه دستگاه را به پايين گودال ميفرستند سپس به وسيله کابل ديگري آنرا روي زمين ميکشند که به اين ترتيب صندوقه از مواد معدني پر ميشود.
ادامه مطلب
Hydrometallurgy Process
Hydrometallurgy, or “hydromet” for short, is a metal processing technology that uses a chemical process combining water, oxygen or other substances in a pressurized or other vessel to dissolve a metal from its ore, concentrate or an intermediate product (such as matte). Further processing is required to produce high purity metal.
The nickel industry worldwide has traditionally smelted concentrates produced from nickel, copper and cobalt sulphide ores to make an intermediate sulphide product called matte. Hydrometallurgy has been used for refining the matte to produce high purity nickel, copper and cobalt for the market. Thus, traditionally production of these metals has occurred in two steps: smelting and refining.
The new hydrometallurgical process that Vale Inco developed will be able to process the nickel concentrate directly to metal products without first having to smelt the concentrate. It will be more economical and environmentally friendly since the sulphur dioxide and dust emissions associated with a smelter are eliminated. The process will also yield more of the valuable cobalt which is lost to a great extent in the smelting process.
This type of hydrometallurgical process is not entirely new. Many operations, some of them in Canada, have used hydrometallurgical processes for years for extraction of zinc and copper from sulphide concentrates. However, it was not until 1990’s that an acid-oxidative hydromet technology was developed to process nickel sulphide concentrates.
Process Description
In the hydromet process for sulphide concentrate, a finely ground nickel-cobalt-copper concentrate will be processed in a pressurized vessel where it will react with oxygen and sulphuric acid to produce an impure solution of nickel, cobalt and copper. This solution will pass through a number of chemical purification steps ending with removal of impurities and separation of nickel, copper and cobalt. The copper and cobalt will be recovered as by-products. The nickel will be recovered by electrolysis as high quality electronickel product suitable for market. The waste solids from the process will be neutralized with lime and will be deposited in a specially designed disposal facility. All water leaving the plant, including precipitation run-off water will be processed to remove contaminants.
Safety
Safety has long been a controversial issue in the mining business especially with sub-surface mining. While mining today is substantially safer than it was in the previous decades, mining accidents are often very high profile, such as the Quecreek Mine Rescue saving 9 trapped Pennsylvania coal miners in 2002. The Courrières mine disaster, Europe's worst mining accident, caused the death of 1,099 miners (including many children) in Northern France on 10 March 1906. It seems that this disaster was surpassed only by the Benxihu Colliery accident in China on April 26, 1942, which killed 1,549 miners.[41] Government figures indicate that 5,000 Chinese miners die in accidents each year, while other reports have suggested a figure as high as 20,000.[42] Mining ventilation is a significant safety concern for many miners. Poor ventilation of the mines causes exposure to harmful gases, heat and dust inside sub-surface mines. These can cause harmful physiological effects, including death. The concentration of methane and other airborne contaminants underground can generally be controlled by dilution (ventilation), capture before entering the host air stream (methane drainage), or isolation (seals and stoppings).[43]
Ignited methane gas is a common source of explosions in coal mines, or, the more violent coal dust explosions. Gases in mines can also poison the workers or displace the oxygen in the mine, causing asphyxiation.[43] For this reason, the MHSA requires that workers have gas detection equipment in groups of miners. It must be able to detect common gases, such as CO, O2, H2S, and % Lower Explosive Limit. Additionally, further regulation is being requested for more gas detection as newer technology such as nanotechnology is introduced.
High temperatures and humidity may result in heat-related illnesses, including heat stroke which can be fatal. Dusts can cause lung problems, including silicosis, asbestosis and pneumoconiosis (also known as miners lung or black lung disease). A ventilation system is set up to force a stream of air through the working areas of the mine. The air circulation necessary for the effective ventilation of a mine is generated by one or more large mine fans, usually located above ground. Air flows in one direction only, making circuits through the mine such that each main work area constantly receives a supply of fresh air.
Miners utilize equipment strong enough to break through extremely hard layers of the Earth's crust. This equipment, combined with the closed workspace that underground miners work in, can cause hearing loss.[44] For example, a roof bolter (commonly used by mine roof bolter operators) can reach sound power levels of up to 115 dB.[44] Combined with the reverberant effects of underground mines, a miner without proper hearing protection is at a high risk for hearing loss[44].
Since mining entails removing dirt and rock from its natural location creating large empty pits, rooms and tunnels, cave-ins are a major concern within mines. Modern techniques for timbering and bracing walls and ceilings within sub-surface mines have reduced the number of fatalities due to cave-ins, but accidents still occur.[citation needed] The presence of heavy equipment in confined spaces also poses a risk to miners, and despite modern improvements to safety practices, mining remains dangerous throughout the world.
Mining techniques
Mining techniques can be divided into two common excavation types: surface mining and sub-surface (underground) mining. Surface mining is much more common, and produces, for example, 85% of minerals (excluding petroleum and natural gas) in the United States, including 98% of metallic ores.[22] Targets are divided into two general categories of materials: placer deposits, consisting of valuable minerals contained within river gravels, beach sands, and other unconsolidated materials; and lode deposits, where valuable minerals are found in veins, in layers, or in mineral grains generally distributed throughout a mass of actual rock. Both types of ore deposit, placer or lode, are mined by both surface and underground methods.
Processing of placer ore material consists of gravity-dependent methods of separation, such as sluice boxes. Only minor shaking or washing may be necessary to disaggregate (unclump) the sands or gravels before processing. Processing of ore from a lode mine, whether it is a surface or subsurface mine, requires that the rock ore be crushed and pulverized before extraction of the valuable minerals begins. After lode ore is crushed, recovery of the valuable minerals is done by one, or a combination of several, mechanical and chemical techniques.
Some mining, including much of the rare earth elements and uranium mining, is done by less-common methods, such as in-situ leaching: this technique involves digging neither at the surface nor underground. The extraction of target minerals by this technique requires that they be soluble, e.g., potash, potassium chloride, sodium chloride, sodium sulfate, which dissolve in water. Some minerals, such as copper minerals and uranium oxide, require acid or carbonate solutions to dissolve.[23][24]
Surface mining is done by removing (stripping) surface vegetation, dirt, and if necessary, layers of bedrock in order to reach buried ore deposits. Techniques of surface mining include; Open-pit mining which consists of recovery of materials from an open pit in the ground, quarrying or gathering building materials from an open pit mine, strip mining which consists of stripping surface layers off to reveal ore/seams underneath, and mountaintop removal, commonly associated with coal mining, which involves taking the top of a mountain off to reach ore deposits at depth. Most (but not all) placer deposits, because of their shallowly buried nature, are mined by surface methods. Landfill mining, finally, involves sites where landfills are excavated and processed.[25]
Sub-surface mining consists of digging tunnels or shafts into the earth to reach buried ore deposits. Ore, for processing, and waste rock, for disposal, are brought to the surface through the tunnels and shafts. Sub-surface mining can be classified by the type of access shafts used, the extraction method or the technique used to reach the mineral deposit. Drift mining utilizes horizontal access tunnels, slope mining uses diagonally sloping access shafts and shaft mining consists of vertical access shafts.
Other methods include shrinkage stope mining which is mining upward creating a sloping underground room, long wall mining which is grinding a long ore surface underground and room and pillar which is removing ore from rooms while leaving pillars in place to support the roof of the room. Room and pillar mining often leads to retreat mining which is removing the pillars which support rooms, allowing the room to cave in, loosening more ore. Additional sub-surface mining methods include hard rock mining which is mining of hard materials, bore hole mining, drift and fill mining, long hole slope mining, sub level caving and block caving
Steps of mine development
The process of mining from discovery of an ore body through extraction of minerals and finally to returning the land to its natural state consists of several distinct steps. The first is discovery of the ore body, which is carried out through prospecting or exploration to find and then define the extent, location and value of the ore body. This leads to a mathematical resource estimation to estimate the size and grade of the deposit. This estimation is used to conduct a pre-feasibility study to determine the theoretical economics of the ore deposit. This identifies, early on, whether further investment in estimation and engineering studies is warranted and identifies key risks and areas for further work. The next step is to conduct a feasibility study to evaluate the financial viability, technical and financial risks and robustness of the project. This is when the mining company makes the decision to develop the mine or to walk away from the project. This includes mine planning to evaluate the economically recoverable portion of the deposit, the metallurgy and ore recoverability, marketability and payability of the ore concentrates, engineering concerns, milling and infrastructure costs, finance and equity requirements and an analysis of the proposed mine from the initial excavation all the way through to reclamation. The proportion of a deposit that is economically recoverable is dependent on the enrichment factor of the ore in the area. Once the analysis determines a given ore body is worth recovering, development begins to create access to the ore body. The mine buildings and processing plants are built and any necessary equipment is obtained. The operation of the mine to recover the ore begins and continues as long as the company operating the mine finds it economical to do so. Once all the ore that the mine can produce profitably is recovered, reclamation begins to make the land used by the mine suitable for future use.
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