Uranium ore mining

The Straz deposit in the Hamr District of the Czech Republic provides a good example of this problem (Slezak, 1997). Starting in 1968, more than 4 Mt of sulfuric acid, 3 X 10 t of nitric acid, and 1.2 X 10 t of ammonia were injected into the subsurface to mine uranium ore. Now, —266 Mm in the North Bohemian Cretaceous Cenomanian and Turonian aquifers are contaminated with uranium, radium, and manganese and other solutes. The contaminated area is more than 24 km and threatens the watershed of the Plucnice River. 

The mined uranium ore is crushed and ground into a fine powder. After ore dressing, the concentrate is leached with sulfuric acid. The solution is treated in a Hq-uid-Hquid extraction, in which uranium is transferred to an organic phase. It is extracted from that with ammonia, and ammonium uranate is precipitated. At 1000°C it is decomposed to yellow uranium oxide UOj. Uranium hexafluoride is prepared by treating the oxide with hydrogen fluoride to make uranium tetrafluoride. This in turn is treated with elemental fluorine to prepare the gaseous hexafluoride UF (sub-Hmation point 56°C). 

MDS Nordion began in 1946 as the radium sales department of Eldorado Mining and Refining (1944) Ltd., an Ottawa-based crown corporation that mined uranium ore, from which radium, a naturally occurring radioactive element, was extracted and refined. Radium was employed extensively in cancer therapy at the time, and Eldorado sold it around the world. In 1947 the Canadian government s nuclear research establishment at Chalk River, Ontario completed a nuclear reactor that began to produce radioisotopes. Since there was a potential market in the medical field for many... 

Several wastes important to DOE are excluded from the RCRA definition of solid wastes (40 CFR 261.2). They include source, special nuclear, or byproduct material as defined by the AEA [Section 11(e), (z), (aa)] waste from extraction, beneficiation, and processing of ores and minerals, including overburden from mining uranium ores utility wastes oil and gas drilling muds and brines and some wastes that are reused or recycled. 

The uraniimi fuel cycle for the uranium-plutonium system is a multicomponent system of chemical process operations that begins with mining uranium ore from the earth as... 

In Situ Leaching. Copper and uranium ores are sometimes leached ia place by circulatiag acidified mine water through the underground deposit. This process is known as solution mining. 

Nonferrous Metal Production. Nonferrous metal production, which includes the leaching of copper and uranium ores with sulfuric acid, accounts for about 6% of U.S. sulfur consumption and probably about the same in other developed countries. In the case of copper, sulfuric acid is used for the extraction of the metal from deposits, mine dumps, and wastes, in which the copper contents are too low to justify concentration by conventional flotation techniques or the recovery of copper from ores containing copper carbonate and siUcate minerals that caimot be readily treated by flotation (qv) processes. The sulfuric acid required for copper leaching is usually the by-product acid produced by copper smelters (see Metallurgy, extractive Minerals RECOVERY AND PROCESSING). 

Uranium is a metal that is found naturally as a constituent of chemical compounds m minerals such as pitchblende. Uranium ore is mined much like coal Open pits are used to mine shallow deposits, deeper deposits require shaft mining. Commercial ores yield 3 to 5 lb of nranitim compounds per ton of ore. A material called yellow-cake is produced that is... 

The presence of radiation in the workplace - which is an inevitable consequence of the radioactivity of uranium - requires that additional safety precautions be taken over and above those observed in other similar workplaces. There are generally three sources from which radiation exposure may occur (i) radiation emitted from uranium ore in-situ and/or during handling (ii) airborne radiation resulting from the decay of radon gas released from the ore and uranium dust and (iii) contamination by ore dust or concentrate. Radiation levels around uranium mining and milling facilities are quite low - for the most part only a few times the natural background levels - and they decrease rapidly as the distance from... 

The amount of solid waste depends on the method of uranium ore exploration. By deep mining, each ton of ore is supplemented by 0.2-0.3 tons of waste ores, and by open pit mining, per 1 ton of ore up to 8-10 tons of excavation materials are produced. Moreover, uranium ores contain from 5% up to 25-30% of waste ores, which are deposited as mine tails. 

The uranium mine tails contain the equal masses of water and solids. Furthermore the treatment of each ton of uranium ore is accompanied by receiving about 3 tons of rafinate, and finally the treatment of 1 ton of uranium ore gives about 4 tons of liquid wastes of different chemical composition, which in turn depends on the treatment technology. 

The relative area of mine solid waste tails (per 100,000 M3 of rock mass) is 0.7-0.8 of the total area. On average, the disturbed areas of uranium ore exploration site are partitioned as follows 32.3% of disturbed land is occupied by dumps, 27.2%, by pits, 20.3%, by industrial areas, 13.3%, by tails, and about 10%, by other types of land disturbance. 

Phytoremediation methods for radionuclide decontamination do not involve hyper-aeeumulators, except possibly for uranium. Plants require a long period of eontact with a contaminant to evolve the ability to hyper-aeeumulate, and most uranium ores are located underground and so are not in eontaet with plants. Soils with high concentrations of uranium are present only where uranium is or has been mined or processed, but these have only been in existenee for a few deeades. 

Fuel. The nuclear fuel cycle starts with mining of the uranium ore, chemical leaching to extract the uranium, and solvent extraction with tributyl phosphate to produce eventually pure uranium oxide. If enriched uranium is required, the uranium is converted to the gaseous uranitim hexafluoride for enrichment by gaseous diffusion or gas centrifuge techniques, after which it is reconverted to uranium oxide. Since the CANDU system uses natural uranium, I will say no more about uranium enrichment although, as I m sure you appreciate, it is a major chemical industry in its own right. 

Mill tailings are wastes produced when uranium ore is mined and then processed. In 2003, there were 26 sites licensed to handle mill tailings in the United States. Most of the sites were no longer processing uranium ore. In addition, another 24 sites have been abandoned. The licensed sites contain about 220 million short tons (200 million metric tons) of mill tailings and the 24 abandoned sites, about 29 million short tons (26 million metric tons) of tailings. 

Uranium is best known as a fuel for nuclear power plants. To prepare this fuel, uranium ores are processed to extract and enrich the uranium. The process begins by mining uranium-rich ores and then crushing the rock. The ore is mixed with water and thickened to form a slurry. The slurry is treated with sulfuric acid and the product reacted with amines in a series of reactions to give ammonium diuranate, (NH4)2U20 . Ammonium diuranate is heated to yield an enriched uranium oxide solid known as yellow cake. Yellow cake contains from 70—90% U3Og in the form of a mixture of U02 and U03. The yellow cake is then shipped to a conversion plant where it can be enriched. 

We should not leave our discussion of nuclear reactors without mentioning the Oklo phenomenon. In 1972, French scientists analyzing uranium ore from the Oklo uranium mine in Gabon found ore that was depleted in 235U. Further investigation showed the presence of high abundances of certain Nd isotopes, which are formed as fission products. The relative isotopic abundances of these isotopes were very different from natural abundance patterns. The conclusion was that a natural uranium chain reaction had occurred 1.8 billion years ago. 

The nuclear fuel cycle (Fig. 16.1) begins with the mining of uranium ore. Uranium is by no means rare. Its overall abundance in Earth s crust is 4 ppm (which is more abundant than Ag, Hg, Bi, or Cd). There are 104 tonnes of uranium in Earth s crust. The problem is one of concentration in that most uranium deposits contain <0.001% uranium. 

After mining, the uranium must be concentrated before further operations are carried out. This is done in the mills, which are located near the mines. Here the uranium ore content is increased from a few tenths of a percent (in the ore) to 85-95% (in a semirefined concentrate known as yellowcake ), while eliminating other elements that are present (the tailings ). 

Solid waste comes from the mining and milling of uranium ore and the sludge from spent fuel storage. It also includes contaminated equipment and structures. High-level solid waste includes the hulls from the dissolving of spent fuel, ion exchange resin, and the like. 

C. A. Fleming, in Vacation School on Uranium Ore Processing , South African Institute of Mining and Metallurgy,... 

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