Uranium mining

From Wikipedia, the free encyclopedia

You have new messages (last change).

Uranium mining is the process of extraction of uranium ore from the ground.

The exploration and mining of radioactive ores in the United States began around the turn of the 20th century. Sources for radium (contained in uranium ore) were sought for use as luminous paint for watch dials and other instruments, as well as for health-related applications (some of which in retrospect were incredibly unhealthy). Because of the need for the element during World War II, the Manhattan Project contracted with numerous vanadium mining companies in the American Southwest, and also purchased uranium ore from the Belgian Congo, through the Union Minière du Haut Katanga, and in Canada from the Eldorado Mining and Refining Limited company, which had large stocks of uranium as waste from its radium refining activities. American uranium ores mined in Colorado were primarily mixes of vanadium and uranium, but because of wartime secrecy the Manhattan Project would only publicly admit to purchasing the vanadium, and did not pay the uranium miners for the uranium ore (in a much later lawsuit, many miners were able to reclaim lost profits from the U.S. government). American uranium ores did not have nearly as high uranium concentrations as the ore from the Belgian Congo, but they were pursued vigorously to ensure nuclear self-sufficiency. Similar efforts were undertaken in the Soviet Union, which did not have native stocks of uranium when it started developing its own weapons program.

Australia has the world's largest uranium reserves - 40 percent of the planet's known supply. Almost all the uranium is exported, but under strict International Atomic Energy Agency safeguards to satisfy the Australian people and government that none of the uranium is used in nuclear weapons. Australian uranium is used strictly for electricity production, but frees other uranium to be used in weapons. 2005 has seen the Australian Government, led by John Howard, leader of the Liberal Party of Australia, propose that Australia increase its uranium mining and build a nuclear reactor to supply energy to the Australian market. The debate continues and will be significant in the next national election.

The Olympic Dam operation run by BHP Billiton in South Australia is combined with mining of copper, gold, and silver, and has reserves of global significance. There are three uranium mines in Australia (a limit currently imposed by the Austalian government), but more have been proposed. The most controversial was Jabiluka, to be built inside the World Heritage listed Kakadu National Park. The existing Ranger Uranium Mine is surrounded by the National Park as the mine area was not included in the original listing of the Park.

In spite of Australia's huge reserves, Canada remains the largest exporter of uranium ore with mines located in Athabasca Basin in northern Saskatchewan. Cameco, the world’s largest, low-cost uranium producer accounting for 18% of the world’s uranium production, operates 3 mines in the area.

Contents

[edit] Exploration

Uranium prospecting is little different than other forms of mineral exploration with the exception of some specialized instruments for detecting the presence of radioactive species.

The Geiger counter was the original radiation detector, recording the total count rate from all energy levels of radiation. Ionization chambers and Geiger counters were first adapted for field use in the 1930's. The first transportable Geiger-Müller counter (weighing 25 kg) was constructed at the University of British Columbia in 1932. H.V. Ellsworth of the GSC built a lighter weight, more practical unit in 1934. Subsequent models were the principle instruments used for uranium prospecting for many years.

The use of airborne detectors to prospect for radioactive minerals was first proposed by G.C. Ridland, a geophysicist working at Port Radium in 1943. In 1947, the earliest recorded trial of airborne radiation detectors (ionization chambers and Geiger counters) was conducted by Eldorado Mining and Refining Limited. (a Canadian Crown Corporation since sold to become Cameco Corporation). The first patent for a portable gamma-ray spectrometer was filed by Professors Pringle, Roulston & Brownell of the University of Manitoba in 1949, the same year as they tested the first portable scintillation counter on the ground and in the air in northern Saskatchewan.

Airborne gamma-ray spectrometry is now the accepted leading technique for uranium prospecting with worldwide applications for geological mapping, mineral exploration & environmental monitoring.

A deposit of uranium, discovered by geophysical techniques, is evaluated and sampled to determine the amounts of uranium materials that are extractable at specified costs from the deposit. Uranium reserves are the amounts of ore that are estimated to be recoverable at stated costs.

[edit] Mining techniques

As with other types of hard rock mining there are several methods of extraction. The main methods of mining are box cut mining, open pit mining and in situ leaching (ISL)

[edit] Open pit

In the early years up until the 1960's uranium was predominantly mined in open pit mines from ore deposits located near the surface. In open pit mining, overburden is removed by drilling and blasting to expose the ore body which is mined by blasting and excavation via loaders and dump trucks. Workers spend much time in enclosed cabins thus limiting exposure. Water is extensively used to suppress airborne dust levels.

[edit] Underground uranium mining

If the uranium is too far below the surface for open pit mining, an underground mine might be used with tunnels and shafts dug to access and remove uranium ore. There is less waste material removed from underground mines than open pit mines, however this type of mining exposes underground worker to the highest levels of radon gas.

Underground uranium mining is in principle no different to any other hard rock mining and other ores are often mined in association (eg copper, gold, silver). Once the ore body has been identified a shaft is sunk in the vicinity of the ore veins, and crosscuts are driven horizontally to the veins at various levels, usually every 100 to 150 metres. Similar tunnels, known as drifts, are driven along the ore veins from the crosscut. To win the ore, the next step is to drive tunnels, known as raises when driven upwards and winzes when driven downwards through the deposit from level to level. These raises are subsequently used to develop the stopes where the ore is mined in the veins.

The stope, which is the workshop of the mine, is the excavation from which the ore is being extracted. Two methods of stope mining are commonly used. In the “cut and fill” method and open stoping method, the space remaining following removal of ore after blasting is filled with waste rock and cement. In the “shrinkage” method just sufficient broken ore is removed via the chutes below to allow the miners to work from the top of the pile to drill and blast for the next layer to be broken off; eventually leaving a large hole. Another method, known as room and pillar, is used for thinner flatter ore bodies. In this method the ore body is first divided into blocks by intersecting drives, removing ore while so doing, and then systematically removing the blocks, leaving sufficient for roof support.

[edit] Heap leaching

Waste rock is produced during open pit mining when overburden is removed, and during underground mining when driving tunnels through non-ore zones.

Piles of these tailings often contain elevated concentrations of radioisotopes compared to normal rock. Other waste piles consist of ore with too low a grade for processing. The transition between waste rock and ore depends on technical and economic feasibility criteria. All these piles threaten people and the environment after shut down of the mine due to their release of radon gas and seepage water containing radioactive and toxic materials.

In some cases uranium has been removed from this low-grade ore by heap leaching. This may be done if the uranium contents is too low for the ore to be economically processed in a uranium mill. The leaching liquid (often sulfuric acid) is introduced on the top of the pile and percolates down until it reaches a liner below the pile, where it is caught and pumped to a processing plant. Due to the potential for extreme damage to the surrounding environment , this practice is no longer in use.

[edit] In situ leaching

In situ leaching, which is sometimes referred to as solution mining, is performed by pumping liquids (weak acid or weak alkaline depending on the density of calcium in the area) down through pipes placed on one side of the deposit of uranium, through the deposit, and up through pipes on the opposing side of the deposit - recovering ore by leaching. ISL is also used on other types of metal extraction such as copper. ISL is cost effective as there is less machinery cost involved. Transfer of excess rock is also an advantage of ISL as there is minimal movement. Less time is involved in set up and maintenance of ISL though it is not suitable to all deposits of uranium as the deposit area must be permeable to the liquids used (for instance in sandstone coverage). Environmental impact studies are performed when surveying exploitable areas mainly because ground water can be affected by ISL. It’s the only type of uranium mining currently being done in the United States (2006).

[edit] Recovery from seawater

The uranium concentration of sea water is low, approximately 3.3 mg per cubic meter of seawater (3.3 ppb) but the quantity of this resource is gigantic (4.5 billion tons), this resource is practically limitless with respect to world-wide demand. That is to say, if even a portion of the uranium in seawater could be used the entire world's nuclear power generation fuel could be provided over a long time period. Although research and development for recovery of this low-concentration element by inorganic adsorbents such as titanium oxide compounds, has occurred since the 1960s in the United Kingdom, France, Germany, and Japan, this research was halted due to low recovery efficiency.

At the Takazaki Radiation Chemistry Research Establishment of the Japan Atomic Energy Research Institute (JAERI Takazaki Research Establishment), research and development has continued culminating in the production of adsorbent by irradiation of polymer fiber. Adsorbents have been synthesized that have a functional group (amidoxime group) that selectively adsorbs heavy metals, and the performance of such adsorbents has been improved. Uranium adsorption capacity of the polymer fiber adsorbent is high, approximately ten fold greater in comparison to the conventional titanium oxide adsorbent. Commercial installations are planned for the near future.

[edit] Rise, stagnation and renaissance of uranium mining

In the beginning of the Cold War, to ensure adequate supplies of uranium for national defense, the United States Congress passed the U.S. Atomic Energy Act of 1946, creating the Atomic Energy Commission (AEC) which had the power to withdraw prospective uranium mining land from public purchase, and also to manipulate the price of uranium to meet national needs. By setting a high price for uranium ore, the AEC created a uranium "boom" in the early 1950s, which attracted many prospectors to the four corners region of the country. Moab, Utah became known as the Uranium-capital of the world, when geologist Charles Steen discovered such an ore in 1952, even though American ore sources were considerably less potent than those in the Belgian Congo or South Africa.

At the height of the nuclear energy euphoria in the 1950s methods for extracting diluted uranium and thorium, found in abundance in granite or seawater, were pursued. ORNL Review Scientists promised that, used in a breeder reactor, these materials would potentially provide limitless source of energy.

American military requirements declined in the 1960s, and the government completed its uranium procurement program by the end of 1970. Simultaneously, a new market emerged: commercial nuclear power plants. However, in the U.S. this market virtually collapsed by the end of the 1970s as a result of industrial strains caused by the energy crisis, popular opposition, and finally the Three Mile Island nuclear accident in 1979, all of which led to a de facto moratorium on the development of new nuclear reactor power stations.

In Europe a mixed situation exists. Considerable nuclear power capacities have been developed, notably in Belgium, France, Germany, Spain, Sweden, Switzerland and the UK. In many countries development of nuclear power has been stopped by legal actions. In Italy the use of nuclear power has been barred by a referendum in 1987. Ireland also has no plans to change it's non-nuclear stance and pursue nuclear power in the future[citation needed].

In France and Switzerland the use of nuclear power continues, but there is little new demand that would stimulate the market for uranium.

In Hungary uranium mining began in the 1950's around Pécs to supply the country's first atomic plant in Paks. After the fall of Socialism uranium mining was gradually given up because of the high production costs. That caused serious economic problems and a rise of unemployment in Pécs.

Since 1981 uranium prices and quantities in the US are reported by the Department of Energy [1]. The import price dropped from 32.90 US$/lb U3O8 in 1981 down to 12.55 in 1990 and to below 10 US$/lb U3O8 in the year 2000. Prices paid for uranium during the 1970s were higher, 43 US$/lb U3O8 is reported as the selling price for Australian uranium in 1978 by the Nuclear Information Centre.

Uranium prices reached an all-time low in 2001, costing US$7/lb, but has since rebounded strongly. As of 2006 Uranium currently sells at US$62.50/lb and the price is still rising. This is the highest price (adjusted for inflation et cetera) in more than 25 years [2]. The higher price has spurred expansion of current mines, construction of new mines and reopening of old mines as well as new prospecting.

[edit] Health risks of uranium mining

Because uranium emits radon gas, and their harmful and highly radioactive daughter products, uranium mining is considerably more dangerous than other (already dangerous) hard rock mining, requiring adequate ventilation systems if the mines are not open pit. During the 1950s, a significant number of American uranium miners were Navajo Indians, as many uranium deposits were discovered on Navajo reservations. A statistically significant subset of these miners later developed small-cell lung cancer, a type of cancer usually not associated with smoking, after exposure to uranium ore and radon-222, a natural decay product of uranium.[3] The radon, which is produced by the uranium, and not the uranium itself has been shown to be the cancer causing agent. [4] Some survivors and their descendants received compensation under the Radiation Exposure Compensation Act in 1990.

[edit] See also

[edit] External links

Retrieved from "http://en.wikipedia.org../../../u/r/a/Uranium_mining.html"
In other languages