
The bismuth-phosphate process was used
to extract plutonium
Plutonium is a chemical element; it has symbol Pu and atomic number 94. It is a silvery-gray actinide metal that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibits six allotropes and four ...
from irradiated uranium taken from
nuclear reactor
A nuclear reactor is a device used to initiate and control a Nuclear fission, fission nuclear chain reaction. They are used for Nuclear power, commercial electricity, nuclear marine propulsion, marine propulsion, Weapons-grade plutonium, weapons ...
s.
It was developed during
World War II
World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
by
Stanley G. Thompson, a chemist working for the
Manhattan Project
The Manhattan Project was a research and development program undertaken during World War II to produce the first nuclear weapons. It was led by the United States in collaboration with the United Kingdom and Canada.
From 1942 to 1946, the ...
at the
University of California, Berkeley
The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California), is a Public university, public Land-grant university, land-grant research university in Berkeley, California, United States. Founded in 1868 and named after t ...
. This process was used to produce plutonium at the
Hanford Site
The Hanford Site is a decommissioned nuclear production complex operated by the United States federal government on the Columbia River in Benton County in the U.S. state of Washington. It has also been known as SiteW and the Hanford Nuclear R ...
. Plutonium was used in the
atomic bomb
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission or atomic bomb) or a combination of fission and fusion reactions (thermonuclear weapon), producing a nuclear expl ...
that was used in the
atomic bombing of Nagasaki
On 6 and 9 August 1945, the United States detonated two atomic bombs over the Japanese cities of Hiroshima and Nagasaki, respectively, during World War II. The aerial bombings killed between 150,000 and 246,000 people, most of whom were civili ...
in August 1945. The process was superseded in the 1950s by the REDOX and
PUREX
PUREX (plutonium uranium reduction extraction) is a chemical method used to purify fuel for nuclear reactors or nuclear weapons. It is based on liquid–liquid extraction ion-exchange. PUREX is the '' de facto'' standard aqueous nuclear reproc ...
processes.
Background
During
World War II
World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
,
plutonium
Plutonium is a chemical element; it has symbol Pu and atomic number 94. It is a silvery-gray actinide metal that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibits six allotropes and four ...
was used to make both the first
atomic bomb
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission or atomic bomb) or a combination of fission and fusion reactions (thermonuclear weapon), producing a nuclear expl ...
ever to be detonated (near Alamogordo, New Mexico) and the atomic bomb that was dropped on Nagasaki in Japan. Plutonium had only been isolated and chemically identified in 1941, so little was known about it, but it was thought that
plutonium-239
Plutonium-239 ( or Pu-239) is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 is also used for that purpose. Plutonium-239 is also one of the three main iso ...
, like
uranium-235
Uranium-235 ( or U-235) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope that exists in nat ...
, would be suitable for use in an atomic bomb.
Producing plutonium on an industrial scale
Plutonium could be produced by irradiating
uranium-238
Uranium-238 ( or U-238) is the most common isotope of uranium found in nature, with a relative abundance of 99%. Unlike uranium-235, it is non-fissile, which means it cannot sustain a chain reaction in a thermal-neutron reactor. However, it i ...
in a
nuclear reactor
A nuclear reactor is a device used to initiate and control a Nuclear fission, fission nuclear chain reaction. They are used for Nuclear power, commercial electricity, nuclear marine propulsion, marine propulsion, Weapons-grade plutonium, weapons ...
,
but developing and building a reactor was a task for the
Manhattan Project
The Manhattan Project was a research and development program undertaken during World War II to produce the first nuclear weapons. It was led by the United States in collaboration with the United Kingdom and Canada.
From 1942 to 1946, the ...
physicists. The task for the chemists was to develop a process to separate plutonium from the other
fission products produced in the reactor, to do so on an industrial scale at a time when plutonium could be produced only in microscopic quantities,
and to do so while working with dangerously radioactive chemicals like
uranium
Uranium is a chemical element; it has chemical symbol, symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Ura ...
—the chemistry of which little was known—and
plutonium
Plutonium is a chemical element; it has symbol Pu and atomic number 94. It is a silvery-gray actinide metal that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibits six allotropes and four ...
, the chemistry of which almost nothing was known.
Experiments with separation methods
Chemists explored a variety of methods for separating plutonium from the other products that came out of the reactor:
*
Glenn Seaborg, one of the chemists who had first isolated and chemically identified plutonium, used
lanthanum fluoride to perform the first successful separation of a weighable quantity of plutonium in August 1942.
This ''lanthanum fluoride process'' became the preferred method for use in the
Manhattan Project's plutonium separation
semiworks at the
Clinton Engineer Works and the production facilities at the
Hanford Site
The Hanford Site is a decommissioned nuclear production complex operated by the United States federal government on the Columbia River in Benton County in the U.S. state of Washington. It has also been known as SiteW and the Hanford Nuclear R ...
, but
the bismuth phosphate process was eventually adopted instead because further work revealed a variety of difficulties with the lanthanum fluoride process:
**Recovering the precipitate through
filtration
Filtration is a physical separation process that separates solid matter and fluid from a mixture using a ''filter medium'' that has a complex structure through which only the fluid can pass. Solid particles that cannot pass through the filte ...
or
centrifugation
Centrifugation is a mechanical process which involves the use of the centrifugal force to separate particles from a solution according to their size, shape, density, medium viscosity and rotor speed. The denser components of the mixture migrate ...
was difficult.
** The lanthanum fluoride process required large quantiles of
hydrogen fluoride
Hydrogen fluoride (fluorane) is an Inorganic chemistry, inorganic compound with chemical formula . It is a very poisonous, colorless gas or liquid that dissolves in water to yield hydrofluoric acid. It is the principal industrial source of fluori ...
, which corroded equipment.
** There were problems stabilizing plutonium in its hexavalent state in the fluoride solution (discovered by Charles M. Cooper of
DuPont
Dupont, DuPont, Du Pont, duPont, or du Pont may refer to:
People
* Dupont (surname) Dupont, also spelled as DuPont, duPont, Du Pont, or du Pont is a French surname meaning "of the bridge", historically indicating that the holder of the surname re ...
, who would be responsible for the design and construction of the facilities).
*
Isadore Perlman and William J. Knox Jr. looked into ''peroxide separation'' because most elements form soluble peroxides in neutral or
acid
An acid is a molecule or ion capable of either donating a proton (i.e. Hydron, hydrogen cation, H+), known as a Brønsted–Lowry acid–base theory, Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis ...
solution. They soon discovered that plutonium was an exception. After a good deal of experimentation, they found that they could precipitate plutonium by adding
hydrogen peroxide
Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...
to a dilute
uranyl nitrate
Uranyl nitrate is a water-soluble yellow uranium salt with the formula . The hexa-, tri-, and dihydrates are known. The compound is mainly of interest because it is an intermediate in the preparation of nuclear fuels. In the nuclear industry, it ...
solution. They were then able to get the process to work, but it produced tons of precipitate, in contrast to the lanthanum fluoride process that produced only kilograms.
* John E. Willard tried an alternative approach, based on the fact that some silicates absorbed plutonium more readily than other elements. This method worked but with low efficiency.
* Theodore T. Magel and Daniel K. Koshland Jr. researched a ''solvent-extraction processes''.
*
Harrison Brown and Orville F. Hill experimented with separation using volatility reactions, based on how uranium could be readily volatilized by
fluorine
Fluorine is a chemical element; it has Chemical symbol, symbol F and atomic number 9. It is the lightest halogen and exists at Standard temperature and pressure, standard conditions as pale yellow Diatomic molecule, diatomic gas. Fluorine is extre ...
.
Discovery and adoption of the bismuth phosphate process
While the chemical engineers worked on these problems, Seaborg asked
Stanley G. Thompson, a colleague at Berkeley, to have a look at the possibility of a ''
phosphate
Phosphates are the naturally occurring form of the element phosphorus.
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthop ...
process'' because it was known that the phosphates of many
heavy metals
upright=1.2, Crystals of lead.html" ;"title="osmium, a heavy metal nearly twice as dense as lead">osmium, a heavy metal nearly twice as dense as lead
Heavy metals is a controversial and ambiguous term for metallic elements with relatively h ...
were insoluble in an acid solutions.
Thompson tried phosphates of
thorium
Thorium is a chemical element; it has symbol Th and atomic number 90. Thorium is a weakly radioactive light silver metal which tarnishes olive grey when it is exposed to air, forming thorium dioxide; it is moderately soft, malleable, and ha ...
, uranium,
cerium
Cerium is a chemical element; it has Chemical symbol, symbol Ce and atomic number 58. It is a hardness, soft, ductile, and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it ...
,
niobium
Niobium is a chemical element; it has chemical symbol, symbol Nb (formerly columbium, Cb) and atomic number 41. It is a light grey, crystalline, and Ductility, ductile transition metal. Pure niobium has a Mohs scale of mineral hardness, Mohs h ...
and
zirconium
Zirconium is a chemical element; it has Symbol (chemistry), symbol Zr and atomic number 40. First identified in 1789, isolated in impure form in 1824, and manufactured at scale by 1925, pure zirconium is a lustrous transition metal with a greyis ...
without success. He did not expect
bismuth
Bismuth is a chemical element; it has symbol Bi and atomic number 83. It is a post-transition metal and one of the pnictogens, with chemical properties resembling its lighter group 15 siblings arsenic and antimony. Elemental bismuth occurs nat ...
phosphate () to work any better, but when he tried it on 18 December 1942, he was surprised to find that it carried 98 percent of the plutonium in solution. The crystalline structure of bismuth phosphate is similar to that of plutonium phosphate, and this became known as the bismuth phosphate process.
Cooper and Burris B. Cunningham were able to replicate Thompson's results, and the bismuth phosphate process was initially adopted as a fallback in case the lanthanum fluoride process could not be made to work. The processes were similar and the equipment used for lanthanum fluoride could be adapted for use with Thompson's bismuth phosphate process. In May 1943, the DuPont engineers decided to adopt the bismuth phosphate process for use in the Clinton semiworks and the Hanford production site.
Discovery of plutonium's two oxidation states
As Brown, Hill, and other chemists explored plutonium chemistry, they made the crucial discovery that plutonium has two oxidation states, a
tetravalent (+4) state and a
hexavalent (+6) state, which have different chemical properties that could be exploited. (This work was performed at the Manhattan Project's Radiation Laboratory at the University of California,
Metallurgical Laboratory at the
University of Chicago
The University of Chicago (UChicago, Chicago, or UChi) is a Private university, private research university in Chicago, Illinois, United States. Its main campus is in the Hyde Park, Chicago, Hyde Park neighborhood on Chicago's South Side, Chic ...
and
Ames Laboratory
Ames National Laboratory, formerly Ames Laboratory, is a United States Department of Energy national laboratory located in Ames, Iowa, and affiliated with Iowa State University. It is a top-level national laboratory for research on national sec ...
at
Iowa State College
Iowa State University of Science and Technology (Iowa State University, Iowa State, or ISU) is a public land-grant research university in Ames, Iowa, United States. Founded in 1858 as the Iowa Agricultural College and Model Farm, Iowa State be ...
.)
Process

The bismuth phosphate process involved taking the irradiated uranium fuel slugs and removing their aluminium cladding. Because there were highly radioactive fission products inside, this had to be done remotely behind a thick concrete barrier. This was done in the "Canyons" (B and T buildings) at Hanford. The slugs were dumped into a dissolver, covered with
sodium nitrate
Sodium nitrate is the chemical compound with the chemical formula, formula . This alkali metal nitrate salt (chemistry), salt is also known as Chile saltpeter (large deposits of which were historically mined in Chile) to distinguish it from ordi ...
solution and brought to a boil, followed by slow addition of
sodium hydroxide
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula . It is a white solid ionic compound consisting of sodium cations and hydroxide anions .
Sodium hydroxide is a highly corrosive base (chemistry), ...
. After removing the waste and washing the slugs, three portions of
nitric acid
Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...
were used to dissolve the slugs.
The second step was to separate the plutonium from the uranium and the fission products.
Bismuth nitrate and
phosphoric acid
Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solution, ...
were added, producing bismuth phosphate, which was precipitated carrying the plutonium with it. This was very similar to the lanthanum fluoride process, in which lanthanum fluoride was used as the carrier.
The precipitate was removed from the solution with a centrifuge and the liquid discharged as waste. Getting rid of the fission products reduced the
gamma radiation
A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...
by 90 percent. The precipitate was a plutonium-containing cake which was placed in another tank and dissolved in nitric acid.
Sodium bismuthate or
potassium permanganate
Potassium permanganate is an inorganic compound with the chemical formula KMnO4. It is a purplish-black crystalline salt, which dissolves in water as K+ and ions to give an intensely pink to purple solution.
Potassium permanganate is widely us ...
was added to oxidize the plutonium. Plutonium would be carried by the bismuth phosphate in the tetravalent state but not in the hexavalent state.
The bismuth phosphate would then be precipitated as a by product, leaving the plutonium behind in solution.
This step was then repeated in the third step. The plutonium was reduced again by adding
ferrous ammonium sulfate. Bismuth nitrate and phosphoric acid were added and bismuth phosphate precipitated. It was dissolved in nitric acid and the bismuth phosphate was precipitated. This step resulted in reducing the gamma radiation by four more orders of magnitude, so the plutonium-bearing solution now had 100,000-th of the original gamma radiation. The plutonium solution was transferred from the 221 buildings to the 224 buildings, through underground pipes. In the fourth step, phosphoric acid was added and the bismuth phosphate precipitated and removed; potassium permanganate was added to oxidize the plutonium.
In the "crossover" step, the lanthanum fluoride process was used. Lanthanum salts and hydrogen fluoride were added again and lanthanum fluoride was precipitated, while hexavalent plutonium was left in solution. This removed
lanthanide
The lanthanide () or lanthanoid () series of chemical elements comprises at least the 14 metallic chemical elements with atomic numbers 57–70, from lanthanum through ytterbium. In the periodic table, they fill the 4f orbitals. Lutetium (el ...
s like cerium,
strontium
Strontium is a chemical element; it has symbol Sr and atomic number 38. An alkaline earth metal, it is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is exposed to ...
and
lanthanum
Lanthanum is a chemical element; it has symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air. It is the eponym of the lanthanide series, a group of 15 similar elements bet ...
, that bismuth phosphate could not. The plutonium was again reduced with
oxalic acid
Oxalic acid is an organic acid with the systematic name ethanedioic acid and chemical formula , also written as or or . It is the simplest dicarboxylic acid. It is a white crystalline solid that forms a colorless solution in water. Its name i ...
and the lanthanum fluoride process was repeated. This time
potassium hydroxide
Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash.
Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which utili ...
was added to
metathesize the solution. Liquid was removed with a centrifuge and the solid dissolved in nitric acid to form plutonium nitrate. At this point, a batch sent would have been concentrated to .
The final step was carried out at the 231-Z building, where hydrogen peroxide, sulfates and
ammonium nitrate
Ammonium nitrate is a chemical compound with the formula . It is a white crystalline salt consisting of ions of ammonium and nitrate. It is highly soluble in water and hygroscopic as a solid, but does not form hydrates. It is predominantly us ...
were added to the solution and the hexavalent plutonium was precipitated as
plutonium peroxide. This was dissolved in nitric acid and put into shipping cans, which were boiled in hot air to produce a plutonium nitrate paste. Each can weighed about 1 kg and was shipped to the
Los Alamos Laboratory
The Los Alamos Laboratory, also known as Project Y, was a secret scientific laboratory established by the Manhattan Project and overseen by the University of California during World War II. It was operated in partnership with the United State ...
. Shipments were made in a truck carrying twenty cans and the first arrived at Los Alamos on 2 February 1945. The plutonium was used in the
Fat Man
"Fat Man" (also known as Mark III) was the design of the nuclear weapon the United States used for seven of the first eight nuclear weapons ever detonated in history. It is also the most powerful design to ever be used in warfare.
A Fat Man ...
bomb design tested in the
Trinity nuclear test on 16 July 1945, and in the
bombing of Nagasaki on 9 August 1945.
Decommissioning
In 1947, experiments began at Hanford on a new REDOX process using
methyl isobutyl ketone (codenamed hexone) as the extractant, which was more efficient. Construction of a
new REDOX plant commenced in 1949 and operations began in January 1952, the B plant closing that year. Improvements to the T plant resulted in a 30 percent increase in productivity and improvements were made to the B plant. There were plans to reactivate the B plant but the new PUREX plant that opened in January 1956 was so efficient that the T plant was closed in March 1956 and plans to reactivate the B plant were abandoned. By 1960, the PUREX plant's output had surpassed the combined output of the B and T plants and the REDOX plant.
Notes
References
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{{portal bar, Chemistry, Nuclear technology
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