Uranium, extraction commercial-processes

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). 

DEPA-TOPO [di (2-ethylhexyl) phosphoric acid and trioctylphosphine oxide] A process for recovering uranium from wet-process phosphoric acid, by solvent extraction with a mixture of the two named reagents. Developed at Oak Ridge National Laboratory and first commercialized in 1978 by Freeport Minerals Corporation and Wyoming Mineral Corporation. 

Solvent extraction plays an important role in many commercial processes for the extraction of uranium from ore. In this case, the radioactivity levels are quite low compared with those in spent fuel extraction. The liquors from hy-drometallurgical leaching of ores are typically fairly dilute in uranium (0.5-5 g/L) and contain iron and other metals in solution. Depending on conditions, solvent extraction or ion exchange may be used to separate and concentrate the uranium from the leach liquor. 

There are a number of practical synergistic systems that make use of organophosphorus compounds. A classic example is the combination of HDEHP and TOPO. The TOPO is thought to replace water or HDEHP in the coordination sphere of the metal. Some early work in this area included a study of the extraction of uranium in such systems (82). Commercial processes now exist for the recovery of uranium from wet-process phosphoric acid utilizing synergistic systems (83,84). Descriptive studies of such systems have also been made (85,86). 

Although the Dapex process is no longer being widely used to extract uranium from sulfuric acid leach liquors, organic phosphoric acids are favored for extracting by-product uranium from commercial phosphoric acid. Organic amines are impractical for this application because they are too fully saturated by the strong acid. 

Conflicting information has been pubUshed on the relative extents of extraction of U and UOj " by dioctyl pyrophosphate. The reduction of the feed acid, which is done in the commercial process, may serve mainly to minimize the coextraction of iron(III), which is extracted much more strongly than iron(II). The uranium(IV) complexes extracted by dialkyl pyrophosphate have been reported to be of the type U(R2HP20v)4, 2 and those of uranium(VI) to be of the type U02(R2P207). However, some doubt was subsequently cast on these conclusions when it was found that the dioctyl pyrophosphate used, which had been prepared by the action of octanol upon phosphorus pentoxide, was a complex mixture of products.Indeed, the strong extractive power of this reagent towards uranium(IV) appears to be the result of a fortuitous synergistic interaction between the components of the mixture. ... 

Tributyl and trioctyl phosphine oxides are also available commercially as extractants. The extraction of uranium from wet process phosphoric acid, as U , can be effected with the latter (TOPO) in kerosine. Other processes devised for this purpose are based on commercial octyl pyrophosphoric acid, or the synergistic mixture 2-ethylhexyl phosphoric acid/trioctyl phosphine oxide in kerosine. For extraction of U +, monooctylphenyl/dioctylphenyl phosphoric acids in kerosine can be employed. TOPO can be used for the extraction of Cr, Zr, Ee, Mo and Sn [18] and for making quantum... 

Solvent Extraction Reagents. Solvent extraction is a solution purification process that is used extensively in the metallurgical and chemical industries. Both inorganic (34,35) and organic (36) solutes are recovered. The large commercial uses of phosphine derivatives in this area involve the separation of cobalt [7440-48-4] from nickel [7440-02-0] and the recovery of acetic acid [61-19-7] and uranium [7440-61-1]. 

Commercial-scale application of solvents coming under the category of neutral reagents is largely found as applied to the nuclear industry materials, as in example, for the separation and refining of uranium, plutonium, thorium, zirconium, and niobium. A process flowsheet for extracting niobium and tantalum from various resources is shown in Figure 5.23. It will... 

The extractant is a commercial mixture of mono- and dioctyl phenyl phosphoric acid (OPPA). It is used in conjuction with tributyl phosphate (TBP). Stripping is by ammonium carbonate solution. The mixture shows synergism. Uranium is extracted in the tetravalent state. The process is much less expensive and possesses a higher extracting power than D2EHPA-TOPO combination. 

Following biological degradation, the extract is exposed to photochemical degradation, which removes uranium from solution as polyuranate. The metals and uranium are captured in separate treatment steps, allowing for the separation of wastes into radioactive and nonradioactive waste streams. This treatment process does not create additional hazardous wastes and allows for the reuse of the contaminated soil. The technology has been the subject of bench-scale tests and is not currently commercially available. 

Organophosphorus acids were among the first extractants to be used in the commercial recovery of uranium from solutions obtained by the leaching of low-grade ores with sulfuric acid. In the so-called Dapex process,70 114 the leach liquor is extracted with a solution of about 0.1 M D2EHPA in kerosene, and the pH value of the aqueous phase is adjusted to close to 1.0 in order to prevent the coextraction of vanadium impurities. Since iron(III) also extracts under these conditions, the leach liquor is reduced with metallic iron prior to extraction to convert any iron(III) present to the iron(II) state. 

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