Concentration of Uranium

The steps in producing refined uranium compounds from crude uranium ores may be conveniently classified into concentration, purification, and conversion to the chemical form finally wanted. Concentration consists in separating uranium from most of the nonuraniferous 

Purification consists in removing from the impure uranium the rest of the nonuraniferous contaminants and producing a pure uranium compound. In most uranium reflneries purification is carried out before conversion of uranium to the chemical form finally wanted. This sequence of refining operations will be described in Secs. 9.2 through 9.6. However, in the process used by the Allied Chemical Company for producing UF from uranium concentrates, the sequence is reversed, with conversion to UF preceding purification of the impure UF by fractional distillation. This process will be described in Sec. 9.7. 

Because of the great variety of natural sources of uranium, no one process is uniquely suited to concentration of uranium from all ores. General methods that have been found useful for certain types of ores will be discussed first and then a few examples will be given of specific processes used for specific ores. Detailed accounts of uranium-concentration processes developed in the United States have been given by Marvin et al. [Ml], Qegg and Foley [Cl], and Merritt [M3]. 

Flotation. Flotation, which is an extremely selective method of concentrating ores of many common elements, is seldom applicable to uranium because few uranium minerals can be selectively floated. 

When the gangue is limestone or some other rock that consumes acid, leaching with sodium or ammonium carbonate is preferred, to reduce chemical consumption and produce a cleaner solution containing lower concentrations of impurities than wdien acid leaching is used. The reactions that occur in carbonate leaching are 

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Some North Dakota lignite ashes have also been observed to have above-average concentrations of uranium (21,22), lea ding to interest in processing the ash for uranium recovery. However, this ash may be classified as hazardous. 

Phosphorite Deposits. Sedimentary phosphorites contain low concentrations of uranium in fine-grained apatite. Uranium of this type is considered an unconventional resource. Significant examples of these uranium ore types include the U.S. deposits in Elorida, where uranium is recovered as a by-product, and the large deposits in North African and Middle Eastern countries (16). 

The concentration of uranium in the analyzed sample, as well as the effectiveness of digestion of the examined materials and the effect of caning material needs to be considered. 

Moore DG (1967) Amazon and Mississippi River concentrations of uranium, thorium, and radium isotopes. Earth Planet Sci Lett 2 231-234... 

The geological term, uranium occurrence, implies a naturally occurring anomalous concentration of uranium. The term, uranium deposit, implies a mass of naturally occurring mineral material from which uranium could be exploited at present or in the future. An often-encountered term in uranium mineralogy is uranium ore mineral. It is a mineral having such physical and chemical properties and occurring in a deposit in such concentra-... 

Korkisch and Koch [106,107] determined low concentrations of uranium in seawater by extraction and ion exchange in a solvent system containing trioctyl phosphine oxide. Uranium is extracted from the sample solution (adjusted to be 1 M in hydrochloric acid and to contain 0.5% of ascorbic acid) with 0.1 M trioctylphos-phine oxide in ethyl ether. The extract is treated with sufficient 2-methoxyethanol and 12 M hydrochloric acid to make the solvent composition 2-methoxyethanol-0.1 M ethereal trioctylphosphine acid-12 M hydrochloric acid (9 10 1) this solution is applied to a column of Dowex 1-X8 resin (Cl" form). Excess of trioctylphosphine oxide is removed by washing the column with the same solvent mixture. Molybdenum is removed by elution with 2-methoxyethanol-30% aqueous hydrogen peroxide-12 M hydrochloric... 

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. 

The concentration of uranium contained in phosphate rocks (50 200 ppm) is higher than that in seawater (see section 12.3.5). Even though economic recovery of uranium from phosphate rock is difficult, several phosphoric acid plants include operation of uranium recovery facilities. 

Applications of cation and anion resins are varied and include purification of sugar, identification of drugs and biomacromolecules, concentration of uranium, calcium therapy to help increase the amount of calcium in our bones (i.e., increase the bone density), and use as therapeutic agents for the control of bile acid and gastric acidity. In the latter use, a solid polyamide (Colestid) is diluted and taken with orange juice, which facilitates removal of bile acids from the body. This removal helps the body to produce more bile acid from cholesterol, thus effectively reducing the cholesterol level. 

Wrenn ME, Singh NP, Paschoa AS, et al. 1985. Concentrations of uranium and thorium isotopes in uranium millers and miners tissues. NTIS NUREG/CR-4382/GAR, 1-47. 

Metals associated with organic materials, inert compounds, or iron oxides may not be recovered during the extraction phase of the technology. Complexed hexavalent uranium has been shown to inhibit the growth of one strain of bacteria used for remediation. The effect becomes more pronounced at higher concentrations of uranium. 

Barrero Moreno et al.49 determined neptunium and plutonium in the presence of high concentrations of uranium by ion chromatography coupled to ICP-MS. 

The variation in oralloy content shown in Column 5 explains some of the variability in s95. Column 5 is calculated on the assumption that the oralloy is 93% 235U. When one considers that UC2 has 90 wt. % of uranium, the concentration of uranium in KH-7 indicates that about half this fraction arose from primary fuel material. 

Isolated concentrations of uranium are found in massive vitrinite without any visible connection with a plane of stratification or a fracture. 

One does not observe decreasing concentrations of uranium as one follows along a stratification plane produced by fracture. 

Earthly abundance of uranium will be described shortly. In terms of presence in seawater, no significant concentrations have been reported. In terms of cosmic abundance, uranium also is very scarce. The study by Harold C Urey (1952), in which silicon was given a base figure of 10,000, the concentration of uranium was represented by a figure of 0.0002. 

The dimeric complex (U02)2A2(HA2)2, reported to be present at low acidities,117 can be formulated similarly (structure 12). At high concentrations of uranium, polymers of increasingly long chains and of composition (U02) A2 2(HA2)2 are formed.118... 

Boomer and Powell [242] have developed an analytical technique using inductively coupled plasma mass spectrometry to estimate the concentration of uranium in a variety of environmental samples including soil. The lower limit for quantitation is 0.1 ng/ml. Calibration is linear from the low limit to 100 ng/ml. Precision, accuracy and a quality control protocol were established. Results are compared with those obtained by the conventional fluorometric method. 

The uranium that is found in roll-front deposits is generally believed to be derived from the dissolution and leaching of host minerals by soil water and ground water (2 3). Typical source rocks for the uranium are granites, tuffs, and tuffaceous sandstones that have relatively high concentrations of uranium in... 

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