Uranium, extraction

Uranium occurs in most phosphate rocks, but its concentration varies from deposit to deposit. Some sedimentary rocks show notably higher concentrations than most igneous rocks. The most uranium-rich rocks found to date are those of Florida (up to 300 ppmw U), Morocco (up to 230 ppmw U), and Jordan (up to 240 ppmw U) [32,33[. In comparison, conventional uranium deposits such as pitchblende typically have a uranium content of 1,000-3,000 ppmw. When the phosphate rock is acidulated, up to 80% or 90% of the ur ium passes into solution in the phosphoric add. The exact amount of PR acidulated depends on its characteristics and the parameters of the phosphoric acid process employed. Examples of the uranium contents of different phosphate rocks and of phosphoric acids produced from them are indicated in Table 11.29. 

The first commercial plant to recover uranium by pre-dpitation in a sodium phosphates operation was built in Illinois, U.S.A. in 1952. Subsequently, in 1955 IMC built a commercial plant based on solvent extraction in Florida another was operated by U.S. Phosphoric Products. 

In the early 1970s, several factors stimulated new interest in uranium recovery. Among these factors were the growth of nuclear programs in the United States 

In the early 1980s eight commercial plants in the United States and one in Canada were recovering uranium from wet-process phosphoric acid. At about the same time, a commercial uranium facility was constructed at the Chimie Rupel subsidiary-of-Societe de Prayon-inr Belgium, and others were planned in France by Rhone-Poulenc and APC, using their own technologies, and in Japan by a consortium headed by the Power Reactor and Nuclear Development Corporation, usirg its own process. 

The technology for the commerdal plants is based c i solvent extraction althoi h other methods have been developed. Much of the development work on solvent extraction was done by the U.S. Government-owned Oak Ridge National Laboratory (ORNL) in Tennessee 134,351. Most of the processes use either octyl pyro-pho horic acid solvent (OPP/, as in the earliest processes in the United States, or various combinations of solvents, developed later by ORNL, di(2-ethylheksyl) phosphoric acid (DEPA), trioctyl phosphine oxide (TOPO), and oct phenylphosphoric add (OPAP). 

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Uranium Extraction from Ore Leach Liquors. Liquid—Hquid extraction is used as an alternative or as a sequel to ion exchange in the selective removal of uranium [7440-61-1] from ore leach Hquors (7,265,271). These Hquors differ from reprocessing feeds in that they are relatively dilute in uranium and only slightly radioactive, and contain sulfuric acid rather than nitric acid. 

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). 

Uses of Nitric Acid. The primary use of nitric acid is for the production of ammonium nitrate for fertilizers. A second major use of nitric acid is in the field of explosives. It is also a nitrating agent for aromatic and paraffinic compounds, which are useful intermediates in the dye and explosive industries. It is also used in steel refining and in uranium extraction. 

Uranium Extraction Technology, A Joint Report by OECD Nuclear Energy Agency and the International Atomic Energy Agency, Paris, 1983. 

Uranium carbonates, 25 430-432 Uranium chlorides, 25 438-439 Uranium compounds, 25 421-434 handling, 17 529 Uranium dioxide, 25 422-423 Uranium-enrichment process gas centrifuge, 25 413-415 Uranium exploration, 25 398 URanium Extraction (UREX) process, 25 420... 

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. 

Uses Plasticizer for lacquers, plastics, cellulose esters, and vinyl resins heat-exchange liquid carbonless copy paper systems in aircraft hydraulic fluids solvent extraction of metal ions from solution of reactor products uranium extraction and nuclear fuel reprocessing pigment grinding assistant antifoaming agent solvent for nitrocellulose and cellulose acetate. 

Preequilibration of the solvent may be required. In some systems, this cost is minimal, but in others it may be high for example, in uranium extraction from sulfate solutions using tertiary amines, the sulfuric acid preequilibration of the solvent before extraction is a few cents or less per pound of UsOg produced. By comparison, in a TBP-HNO3 system for the recovery of zirconium, the preequilibration costs, using nitric acid, amount to about 50 cents per pound of Zr produced. 

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. 

High-grade pitchblende ores are leached with nitric acid to recover uranium. Extraction of uranium from nitrate solutions is usually performed with TBP. TBP-based solvents are used in several areas of the nuclear industry, especially for reprocessing of spent nuclear fuels and for refining the uranium product of the Amex and Dapex processes. Extraction of uranium by TBP solvents is described in sections 12.3.4 and 12.5. 

Various processes have been used for uranium extraction from phosphoric acid solution their main features are listed in Table 12.4. The HDEHP-TOPO process is increasingly preferred over others because of the stability of the extractant and the well-understood chemistry of the process. 

The essential ingredients for producing heat in a thermal fission nuclear reactor are the fuel and a moderator. A heat transport system with its coolant is necessary to convey the heat from the reactor to boilers where steam is produced to drive the turbogenerator. The natural materials available for fuel and moderator are uranium ore and water natural uranium extracted from the ore comprises the fissionable isotope uranium-235 and water contains hydrogen which is a good moderator. (Table I)... 

Figure 15 The effect of uranium concentration on uranium extraction from H2S04 by 0.1 M HDEHP in kerosene.106 The curves are labelled with U concentration (g dm-3)...

Uranium extracted by HDEHP may be returned to the aqueous phase by contact with a strong acid, which reverses the extraction reaction. Alternatively, contact with sodium carbonate solution may be used to strip the U022+ from the organic phase as carbonate complexes. This approach is used in the DAPEX process and reactions such as that given by equation (60) may be proposed to represent the transfer process. 

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