Molten salt metal extraction

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... 

Pu metal has recently been produced in kilogram batches in a coordinated reduction-purification sequence (pyrochemical processing) with Ca reductant, CaCL flux, and subsequent molten salt Am extraction (9.2.2.6.1), yielding single ingots of Pu metal. ... 

Liquid-liquid extraction is possible in non-aqueous systems In a system consisting of a molten metal in contact with molten salt, metals can be extracted from one phase to the other. This is related to a mercury electrode where a metal can be reduced, the metal will often then dissolve in the mercury to form an amalgam that modifies its electrochemistry greatly. For example, it is possible for sodium cations to be reduced at a mercury cathode to form sodium amalgam, while at an inert electrode (such as platinum) the sodium cations are not reduced. Instead, water is reduced to hydrogen. A detergent or fine solid can be used to stabilize an emulsion, or third phase. 

Figure 3 shows a flowsheet for plutonium processing at Rocky Flats. Impure plutonium metal is sent through a molten salt extraction (MSE) process to remove americium. The purified plutonium metal is sent to the foundry. Plutonium metal that does not meet foundry requirements is processed further, either through an aqueous or electrorefining process. The waste chloride salt from MSE is dissolved then the actinides are precipitated with carbonate and redissolved in 7f1 HN03 and finally, the plutonium is recovered by an anion exchange process. 

MSE Processing of High-Grade Plutonium Scrap. Americium is remove3 from plutonium in a liquid-liquid extraction process using molten salt (KC1, NaCl, MgCl2) and molten plutonium metal... 

An overview is presented of plutonium process chemistry at Rocky Flats and of research in progress to improve plutonium processing operations or to develop new processes. Both pyrochemical and aqueous methods are used to process plutonium metal scrap, oxide, and other residues. The pyrochemical processes currently in production include electrorefining, fluorination, hydriding, molten salt extraction, calcination, and reduction operations. Aqueous processing and waste treatment methods involve nitric acid dissolution, ion exchange, solvent extraction, and precipitation techniques. 

R. C. "Molten Salt Extraction of Americium from Molten Plutonium Metal," U.S. ERDA Rept. RFP-2365, Dow Chemical Co., Golden, Colorado, March 12, 1976. 

The following pages will describe several examples of pyrochemical processing as applied to the recycle of plutonium, and will briefly review the fundamental chemistry of these processes. We shall review the conversion of plutonium oxide to plutonium metal by the direct oxide reduction process (DOR),the removal of americium from metallic plutonium by molten salt extraction (MSE), and the purification of metallic... 

Figure 10 shows in graphic form the utility of molten salt extractions for americium removal in one, two, and three stage extractions for various salt-to-metal extraction feeds. This graph demonstrates the impressive power of molten salt extraction systems for purification of plutonium from americium and related rare earth elements. 

The very chemically reactive plutonium hydride is usually decomposed in a vacuum-tight furnace capable of attaining a temperature of 700°C. Plutonium hydride that is decomposed under vacuum at temperatures below 400°C forms a very fine (<20y) metallic powder above 500°C the powder begins to sinter into a porous frit which melts at 640°C to form a consolidated metal ingot. This metal typically contains significant oxide slag but is suitable for feed to either molten salt extraction or electrorefining. 

Long, J.L. Perry, C.C. "The Molten Salt Extraction of Americium from Plutonium Metal", Nuc. Metal 15 p. 385 (1969). 

Knighton, J.B. Auge, R.G. Berry, J.W. "Molten Salt Extraction of Americium from Molten Plutonium Metal", Rocky Flats Plant report RFP-2365 (1976). 

Molten Salt Extraction. The metal from DOR and PuF4 reduction is impure and proceeds to the next step in the process sequence... 

Americium Extraction (more commonly referred to as Molten Salt Ex-or MSE). This process is specifically designed to reduce the americium content of the plutonium metal. (Am241 spontaneously grows into plutonium as a result of Pu241 decay.) When the impure metal contains more than 1000 ppm of americium, it is run through the MSE process. Otherwise, it bypasses the MSE step and proceeds directly to electrorefining. 

Molten Salt Extraction Salts Plutonium and Americium Recovery. We have demonstrated the ability to successfully strip the plutonium from the MSE salts. The resulting metal product now contains as much as 10% americium and as a result cannot be fed directly into the metal processing sequence. To use the plutonium we must remove the americium. 

The alkali metals are the most violently reactive of all the metals. They are too easily oxidized to be found in the free state in nature and cannot be extracted from their compounds by ordinary chemical reducing agents. The pure metals are obtained by electrolysis of their molten salts, as in the electrolytic Downs process (Section 12.13) or, in the case of potassium, by exposing molten potassium chloride to sodium vapor ... 

N. Q. Minh, Extraction of Metals by Molten Salt Electrolysis Chemical Fundamentals And Design Factors, J. Metals, p. 28, Jan. 1985. 

T0535 Molten Metal Technology, Inc., Quantum Catalytic Extraction Process (Q-CEP) T0536 Molten Salt Oxidation—General... 

The metals of these two families are studied together because they are extremely active base-forming elements. On account of their great activity they are never found uncombined in nature, and it is only by the aid of the most powerful reducing agencies (for example, by electrolysis of their molten salts) that the metals themselves are extracted from their compounds. 

The most used liquid metal pool electrode is the aluminum cathode (m.p. 660°C) in the Hall-Heroult aluminum extraction cell. Alkali metals and alkaline-earth metals are also used as liquid cathodes in their molten salt extraction processes. 

This paper is presented in two parts Part I, Molten Salt Extraction of Americium From Molten Plutonium Metal and Part II, "Aqueous Recovery of Americium From Extraction Salts."... 

MOLTEN SALT EXTRACTION OF AMERICIUM FROM MOLTEN PLUTONIUM METAL... 

Americium is separated from plutonium by a liquid-liquid extraction process involving immiscible molten salt and molten plutonium metal phases. The molten salt extraction process is based upon equilibrium partitioning (by oxidation-reduction reactions) of americium and plutonium between the molten chloride salt and molten plutonium metal phases. 

In the molten salt extraction process, the variables that control the values of the americium and plutonium distribution coefficients are temperature, metal composition, salt composition, and total americium. To minimize the variables, the extractions are conducted at a fixed temperature of about 750°C. Slight changes of magnesium content in the metal have a negligible effect upon the value of the americium and plutonium distribution coefficients. The effect of americium concentration... 

Two unit operations are used in the equilibration of the salt and metal phases (1) intermixing of salt and metal, and (2) disengagement of salt and metal. Because this is a batch extraction, both operations (intermixing and disengagement of phases) occur sequentially in the same vessel. For practical operation of the molten salt extraction process, attainment of equilibrium or near-equilibrium conditions (when the value of F approaches 1) in a relatively short period of time is essential. 

Salt and metal insoluble impurities, such as Pu02, associated with plutonium metal are taken up by the salt in Stage 1. Stage 2 is essentially free of these impurities. Strickland, et al. (14), reported that plutonium oxide extracts americium from molten plutonium metal in a molten salt media. Because these salt and metal insoluble impurities are present in sizable amounts only in Stage 1, the side reaction between americium and these impurities occurs only in Stage 1. The side reaction term (B) is introduced to quantify the side reaction caused by the presence of impurities such as in Stage 1. 

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