Uranium, extraction development

Seawater. The world s oceans contain ca 4 X 10 t of uranium (32). Because the uranium concentration is very low, approximately 3.34 ppm, vast amounts of water would be required to recover significant amount of uranium metal, ie, 10 m of seawater for each metdc ton of U. Significant engineering development and associated environmental concerns have limited the development of an economic means of uranium extraction from seawater (32) (see Ocean RAWMATORiALs). 

Eluex An early process for extracting uranium from its ores, using both ion-exchange and solvent extraction. Developed by the National Lead Company, United States. 

Another potentially vast resource is seawater. Uranium resources associated with the oceans are estimated at around 4000 million tonnes however, the uranium concentration in seawater is only around 0.003 ppm. The recovery of uranium from seawater is still subject to basic research. Considerable technological developments as well as significant improvements of economics (or drastic increases in uranium prices) are crucial for the commercial use of this resource, which is unlikely in the foreseeable future. As the energy demand for uranium extraction increases with lower concentrations, the net energy balance of the entire fuel cycle is also critical. 

The solvent extraction process that uses TBP solutions to recover plutonium and uranium from irradiated nuclear fuels is called Purex (plutonium uranium extraction). The Purex process provides recovery of more than 99% of both uranium and plutonium with excellent decontamination of both elements from fission products. The Purex process is used worldwide to reprocess spent reactor fuel. During the last several decades, many variations of the Purex process have been developed and demonstrated on a plant scale. 

In order to make use of thorium as a nuclear resource for power generation, development of efficient separation processes are necessary to recover 233U from irradiated thorium and fission products. The THORium uranium Extraction (THOREX) process has not been commercially used as much as the PUREX process due to lack of exploitation of thorium as an energy resource (157,180). Extensive work carried out at ORNL during the fifties and sixties led to the development of various versions of the THOREX process given in Table 2.6. The stable nature of thorium dioxide poses difficulties in its dissolution in nitric acid. A small amount of fluoride addition to nitric acid is required for the dissolution of more inert thorium (181). 

UREX [URanium Extraction] A solvent extraction process for extracting uranium and technetium from used nuclear fuel, while rejecting all the transuranic elements. Based on the Purex process, which uses tributyl phosphate in a hydrocarbon mixture, but incorporating acetohydroxamic acid, which complexes the Pu and Np and thereby prevents them from being extracted. Developed by the Westinghouse Savannah River Company in 2003. Associated processes are NPEX, TRUEX, and Cyanex 301. 

The EPA developed two methods for the radiochemical analysis of uranium in soils, vegetation, ores, and biota, using the equipment described above. The first is a fusion method in which the sample is ashed, the silica volatilized, the sample fused with potassium fluoride and pyrosulphate, a tracer is added, and the uranium extracted with triisooctylamine, purified on an anion exchange column, coprecipitated with lanthanum, filtered, and prepared in a planchet. Individual uranium isotopes are separately quantified by high resolution alpha spectroscopy and the sample concentration calculated using the yield. The second is a nonfusion method in which the sample is ashed, the siUca volatilized, a tracer added, and the uranium extracted with triisooctylamine, stripped with nitric acid, co-precipitated with lanthanum, transferred to a planchet, and analyzed in the same way by high resolution a-spectroscopy (EPA 1984). 

A time resolved iasCT induced fluorescence (TRLIF) system has been developed for the on-line measurement of uranyl chelates in supercritical carbon dioxide. This system has been applied to the study of dynamic supercritical uranium extraction processes. Fundamental physical parameters such as conq>lex solubility and distribution coefficients can also be detnmined with TRLIF. 

The ORNL research program resulted in the development of two basic processes. These processes are similar as far as equipment is concerned, and they differ only in the solvent used [36]. Uranium extraction is achieved in a process that comprises two cycles (Figure 11.28). In the first cycle, uranium is extracted from phosphoric acid with an organic solvent in five stages and then stripped from this solvent with fresh phosphoric acid,... 

Ammonium carbonate leaching has been developed specifically for uranium extraction from the ore at Grand Junction, Colorado. The technique and plant resembles that used for sodium carbonate pressure leach. 

The early organic solvents to be developed for uranium extraction at higher concentrations were for use with nitrate solutions, and were there-... 

Wang, T., Khangaokar, T., Long, W. et al. (2014). Development of a kelp-type strueture module in a coastal ocean model to assess the hydrodynamic impact of seawater uranium extraction technology, J. Marine Sci. Eng. 2, 81-92. 

TVEX-TBP properties were used to develop the biggest full-scale application of TVEX-TBP in the former USSR for uranium extraction at uranium ore-processing... 

The development of the novel Davy-McKee combined mixer—settler (CMS) has been described (121). It consists of a single vessel (Fig. 13d) in which three 2ones coexist under operating conditions. A detailed description of units used for uranium recovery has been reported (122), and the units have also been studied at the laboratory scale (123). AppHcation of the Davy combined mixer electrostatically assisted settler (CMAS) to copper stripping from an organic solvent extraction solution has been reported (124). 

PEI derivatives have proven to be effective carriers of cations in Hquid membrane systems (404). This technology led to the development of ion-exchange resins (405), which are also suitable for extracting uranium from seawater (406). 

An improved solvent extraction process, PUREX, utilizes an organic mixture of tributyl phosphate solvent dissolved in a hydrocarbon diluent, typically dodecane. This was used at Savannah River, Georgia, ca 1955 and Hanford, Washington, ca 1956. Waste volumes were reduced by using recoverable nitric acid as the salting agent. A hybrid REDOX/PUREX process was developed in Idaho Falls, Idaho, ca 1956 to reprocess high bum-up, fuUy enriched (97% u) uranium fuel from naval reactors. Other separations processes have been developed. The desirable features are compared in Table 1. 

Dissolved Minerals. The most significant source of minerals for sustainable recovery may be ocean waters which contain nearly all the known elements in some degree of solution. Production of dissolved minerals from seawater is limited to fresh water, magnesium, magnesium compounds (qv), salt, bromine, and heavy water, ie, deuterium oxide. Considerable development of techniques for recovery of copper, gold, and uranium by solution or bacterial methods has been carried out in several countries for appHcation onshore. These methods are expected to be fully transferable to the marine environment (5). The potential for extraction of dissolved materials from naturally enriched sources, such as hydrothermal vents, may be high. 

PoUowing further development (38), a two-cycle process has been adopted by industry. In the first concentration cycle, the clarified feed acid containing 100—200 mg/L U Og [1334-59-8] is oxidized, for example, with hydrogen peroxide or sodium chlorate [7775-09-9] to ensure that uranium is in its 6+ valence state is not extracted. Uranium is extracted with a solvent composed of 0.5 Af D2EHPA and 0.125 Af TOPO dissolved in an aUphatic hydrocarbon diluent. 

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). 

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