Salting agent extraction

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. 

Research should continue on traditional separation methods. For example, there is a continuing need for more selective extraction agents for liquid-liquid and ion-exchange extractions. High-temperature processes that use liquid metals or molten salts as extraction agents should have potential in nuclear fuel reprocessing and... 

Depending on the amount of amine used and on the milling time, the reaction mass either had a pastelike consistency or that of a fluid dispersion. The experiments were intended to establish some parameters (duration of mechanical processing, amount of diamine and complexing agent, etc.) and correlate them to characterize the polymers obtained, and to determine certain chemical and physical properties of the polymer. In all cases, the samples were purified by extraction in a Soxhlet apparatus with water or alcohol to remove unreacted ethylenediamine and metallic salts. The extractions were carried out until constant weight was obtained. Total removal of chloride was determined by silver nitrate. Purified samples were then washed with methanol, dried, and analyzed. 

Very recently, zeolites have also been modified by chlorine (13) and chlorine-related compounds at high temperature (14, 15). The known modification methods can be further classified as either liquid or vapor phase treatments. The acid washing, organic complexing agent extraction and chromic salt treatments fall into the first class while the steaming and the chlorine and related compounds reactions belong to the second class. 

For the fluorometric method, uranium is concentrated by co-precipitation with aluminum phosphate, dissolved in diluted nitric acid containing magnesium nitrate as a salting agent, and the co-precipitated uranium is extracted into ethyl acetate and dried. The uranium is dissolved in nitric acid, sodium fluoride flux is added, and the samples fused over a heat source (EPA 1980). 

Separation by solvent extraction Uranium can be extracted from aqueous solutions using extraction agents into the solvent phase, from which it can be stripped. The extraction agents used are phosphorus compounds such as di-(2-ethylhexyl)-phosphate, tri-n-butyl-phosphate and tri-n-octylphosphine oxide as well as primary, secondary and tertiary amines in salt form or as quaternary ammonium salts. The extraction agents are diluted with inert hydrocarbons, preferably kerosene, to concentrations of 4 to 10% by volume. The solubility of the amine salts, particularly the hydrogen sulfates, chlorides and nitrates is increased by adding long chain alcohols (e.g. isodecanol). 

The TBP extraction process. The extraction of trivalent actinides by TBP may succeed, as well known, at low acidity conditions, provided a sufficient nitrate salt content is reached in the feed solution (13,14). However, the large amount of salting agents to be added to the HAW (tons of Na and Al nitrate per ton of spent... 

As illustrated in Fig. 4.15, different equilibrium lines can exist for the extracting and scrubbing sections, as might occur if the scrub solution contains a different salting agent... 

The solvent used in the Redox process was hexone, methyl isobutyl ketone, an extractant already in use for purifying uranium ore concentrates (Chap. 5)., Hexone is immiscible with water and will extract uranyl nitrate and plutonyl nitrate selectively from fission-product nitrates if the aqueous solution has a sufficiently high nitrate ion concentration. In the Redox process, aluminum nitrate was used as salting agent because high concentrations of nitric acid would decompose the hexone solvent. 

A modification of the Redox process, the U-hexone process, was used at the Idaho Chemical Processing Plant of the U.S. AEC, to recover highly enriched uranium from U-A1 alloy fuel elements irradiated in the Materials Testing Reactor. The aluminum nitrate needed as salting agent was provided when the fuel was dissolved in nitric acid. The plutonium content of the fuel was too low to warrant recovery. Plutonium was made trivalent and inextractable before solvent extraction and thus routed to the aqueous high-level waste. 

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