Extraction process, molten salt

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. 

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. 

Molten salt extraction residues are processed to recover plutonium by an aqueous precipitation process. The residues are dissolved in dilute HC1, the actinides are precipitated with potassium carbonate, and the precipitate redissolved in nitric acid (7M) to convert from a chloride to a nitrate system. The plutonium is then recovered from the 7M HNO3 by anion exchange and the effluent sent to waste or americium recovery. We are studying actinide (III) carbonate chemistry and looking at new... 

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... 

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

Molten Salt Extraction (MSE) - Salt Recovery. The salt residue from the americium extraction process is made up of NaCl, KC1, MgCl2, PuCl3, and AmCl3. A typical residue weighs approximately 2.0 kg and contains 200 g plutonium, 10-20 g americium, 50 g MgCl3 with the remaining equimolar NaCl-KCl. 

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. 

Chloride slagging process—See Molten salt extraction... 

Molten salt distillation, of hafnium, 13 84 Molten salt extraction (MSE) process, 19 677... 

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. 

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. 

An optimum molten salt extraction process at Rocky Flats would use the minimum amount of salt required to obtain (1) a desired removal of americium, (2) a minimum transfer of plutonium to the salt, and (3) a minimum take-up of magnesium by the plutonium metal product. The product salt must be compatible with subsequent chemical processes for the recovery of americium and plutonium contained in the salt. To minimize the number of glove-box operations, time in the gloves, and operator radiation exposure, the operations must be simple and easy to conduct. By using the minimum amount of salt feed, a minimum amount of waste will be generated that ultimately must be sent to long-term storage. 

To optimize the molten salt extraction process, the values of the terms in the extraction factor relationship... 

One step in the pyrochemical processing of Pu (9.2.2.1) is molten-salt extraction of Am from Pu metal in an alkali chloride-MgCl2 melt. Americium has greater reducing strength than Pu toward MgCl2, and the molten salt extraction exploits this property. ... 

The Rocky Flats Plant (RFP) has a large recovery facility to recover plutonium from miscellaneous scraps and residues a byproduct in the plutonium recovery stream is americium from the decay of plutonium-241. Currently a NaCl-KCl-MgClo eutectic salt is used at Rocky Flats to separate americium from plutonium in a molten salt extraction (MSE) process. 

A two-stage, countercurrent molten-salt extraction process is used to extract Am from many kilograms of aged plutonium metal in which Am has grown-in by beta decay of Pu. The purification scheme, based partly on molten-halide/molten-metal studies at the Los Alamos Scientific Laboratory and Argonne National Laboratory, ronoves about 90% of the americium from plutonium metal, typically containing 200 2000 ppm Am [16]. 

Proctor, S. G. (1975) Cation Exchange Process for Molten Salt Extraction Residues, USERDA Report RFP-2347, Rocky Flats Plant, Dow Chemical Company. Campbell, D. O. (1970) Ind. Eng. Chem. Process Des. Dev. 9, 95-9. 

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... 

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