Bismuth phosphate process

The first successflil production method for the separation of Pu from U and its fission products was the bismuth phosphate process, based on the carrying of Pu by a precipitate of BiPO (126). That process has been superseded by Hquid-Hquid extraction (qv) and ion exchange (qv). In the Hquid-Hquid... 

The oldest, most well-established chemical separation technique is precipitation. Because the amount of the radionuclide present may be very small, carriers are frequently used. The carrier is added in macroscopic quantities and ensures the radioactive species will be part of a kinetic and thermodynamic equilibrium system. Recovery of the carrier also serves as a measure of the yield of the separation. It is important that there is an isotopic exchange between the carrier and the radionuclide. There is the related phenomenon of co-precipitation wherein the radionuclide is incorporated into or adsorbed on the surface of a precipitate that does not involve an isotope of the radionuclide or isomorphously replaces one of the elements in the precipitate. Examples of this behavior are the sorption of radionuclides by Fe(OH)3 or the co-precipitation of the actinides with LaF3. Separation by precipitation is largely restricted to laboratory procedures and apart from the bismuth phosphate process used in World War II to purify Pu, has little commercial application. 

In the first separation procedure operated in a technical scale, was separated as Pu(IV) from U and fission products by coprecipitation with BiP04 (bismuth phosphate process). Today, solvent extraction is applied, because it leads to higher decontamination factors and can be operated as a continuous process. 

Seaborg and associates [LI] had found that tetravalent plutonium [Pu(IV)] could be coprecipitated from aqueous solution in good yield with insoluble bismuth phosphate BiP04, made by adding bismuth nitrate and sodium phosphate to an aqueous solution of plutonium nitrate. The bismuth phosphate process was developed at the Metallurgical Laboratory, demonstrated at the X-10 pilot plant at Oak Ridge National Laboratory in 1944, and put into operation for large-scale recovery of plutonium from irradiated fuel at Hanford in early 1945. 

The bismuth phosphate process consisted of a number of steps in which plutonium is made alternatively soluble and insoluble. Fuel elements containing plutonium, uranium, and fission products were first dissolved in nitric acid. Plutonium was reduced to the tetravalent state by addition of sodium nitrite. Plutonium phosphate Pu3 (P04)4 was coprecipitated with bismuth phosphate BiP04, by addition of bismuth nitrate and sodium phosphate. Coprecipitation of uranium was prevented by the presence of sufficient sulfate ion to form anionic UO2(804)2. The BiP04 precipitate was redissolved in nitric acid and subjected to two decontamination cycles to purify the plutonium. In each cycle the plutonium was oxidized to the soluble hexavalent state by NaBiOs or other strong oxidant. Next bismuth phosphate was again precipitated, to remove fission products while hexavalent plutonium remained in solution. Then plutonium was reduced to the tetravalent state and again coprecipitated with bismuth phosphate. 

Purex plant. Reprocessing was first done by the bismuth phosphate process, operational in 1944. Ferrous sulfamate. 

Irradiated Fuel A historically important and continuing mission at the Hanford site is to chemically process irradiated reactor fuel to recover and purify weapons-grade plutonium. Over the last 40 years, or so, several processes and plants— Bismuth Phosphate, REDOX, and PUREX—have been operated to accomplish this mission. Presently, only the Hanford PUREX Plant is operational, and although it has not been operated since the fall of 1972, it is scheduled to start up in the early 1980 s to process stored and currently produced Hanford -Reactor fuel. Of nine plutonium-production reactors built at the Hanford site, only the N-Reactor is still operating. 

The discovery of nuclear fission in 1938 proved the next driver in the development of coordination chemistry. Uranium-235 and plutonium-239 both undergo fission with slow neutrons, and can support neutron chain reactions, making them suitable for weaponization in the context of the Manhattan project. This rapidly drove the development of large-scale separation chemistry, as methods were developed to separate and purify these elements. While the first recovery processes employed precipitation methods (e.g., the bismuth phosphate cycle for plutonium isolation). 

Experiments on this ultra-microchemical scale were performed to test the chemical process for separating the plutonium produced during the war by the chain reaction at Hanford, Washington. This process used bismuth phosphate as a carrier material, and it was conceived and worked out in... 

Seaborg s team developed two separation processes to take advantage of the different chemistries of plutonium s several different valence states. One process used bismuth phosphate as a carrier the other used lanthanum fiuoride. Bismuth phosphate, scaled up directly from Met Lab experiments, served the primary purpose of uranium and fission-product decontamination. Lanthanum fiuoride, applied at pilot scale at Oak Ridge, then concentrated the plutonium from the large volume of solution in which it was suspended. 

Construction of the chemical concentration buildings (224-T, -U, and -B) was a less daunting task because relatively little radioactivity was involved, and the work was not started until very late 1944. The 200-West units were finished in early October, the East unit in February 1945. In the Queen Marys, bismuth phosphate carried the plutonium throu the long succession of process pools. The... 

In the processing of nuclear materials, precipitation/coprecipitation techniques are used for the separation of the actinides from most fission products. Both fluoride and oxalate complexes of these metal ions are sufficiently insoluble to accomplish this separation (Stary 1966). Coprecipitation with bismuth phosphate has also been used for this purpose (Stary 1966). Because of their insensitivity to subtle changes induced by minor cation-radius changes, such techniques are not useful for the separation of the lanthanides from the trivalent actinide metal ions. 

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