Yellowcake (also called urania) is a type of

uranium Uranium is a chemical element with the 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. Uranium is weak ...

concentrate powder obtained from leach solutions, in an intermediate step in the processing of uranium ores. It is a step in the processing of uranium after it has been mined but before fuel fabrication or

uranium enrichment Enriched uranium is a type of uranium in which the percent composition of uranium-235 (written 235U) has been increased through the process of isotope separation. Naturally occurring uranium is composed of three major isotopes: uranium-238 (238 ...

. Yellowcake concentrates are prepared by various extraction and refining methods, depending on the types of ores. Typically, yellowcakes are obtained through the milling and chemical processing of uranium ore, forming a coarse powder that has a pungent odor, is insoluble in water, and contains about 80% uranium oxide, which melts at approximately 2880 °C.

Overview

Originally raw uranium ore was extracted by traditional mining and this is still the case in many mines. It is first crushed to a fine powder by passing it through crushers and grinders to produce "pulped" ore. This is further processed with concentrated

acid In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a se ...

alkaline In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a ...

, or

peroxide In chemistry, peroxides are a group of compounds with the structure , where R = any element. The group in a peroxide is called the peroxide group or peroxo group. The nomenclature is somewhat variable. The most common peroxide is hydrogen p ...

solutions to leach out the uranium. However, nearly half of yellowcake production is now produced by in situ leaching in which the solution is pumped through the uranium deposit without disturbing the ground. Yellowcake is what remains after drying and filtering. The yellowcake produced by most modern mills is actually brown or black, not yellow; the name comes from the color and texture of the concentrates produced by early mining operations.

Initially, the compounds formed in yellowcakes were not identified; in 1970, the U.S. Bureau of Mines still referred to yellowcakes as the final precipitate formed in the milling process and considered it to be

ammonium diuranate Ammonium diuranate or (ADU) ((NH4)2U2O7), is one of the intermediate chemical forms of uranium produced during yellowcake production. The name "yellowcake" originally given to this bright yellow salt, now applies to mixtures of uranium oxides which ...

or sodium diuranate. The compositions were variable and depended upon the leachant and subsequent precipitating conditions. The compounds identified in yellowcakes include uranyl hydroxide, uranyl sulfate, sodium para-uranate, and uranyl peroxide, along with various uranium oxides. Modern yellowcake typically contains 70% to 90% triuranium octoxide (U₃O₈) by weight. Other oxides such as

uranium dioxide Uranium dioxide or uranium(IV) oxide (), also known as urania or uranous oxide, is an oxide of uranium, and is a black, radioactive, crystalline powder that naturally occurs in the mineral uraninite. It is used in nuclear fuel rods in nuclear re ...

(UO₂) and uranium trioxide (UO₃) exist. Yellowcake is produced by all countries in which uranium ore is mined.Gil, Laura (2018)
"Uranium leaching: How yellowcake is made"
IAEA Bulletin (Online), vol. 59, iss, 2, pp. 22-23.

Further processing

Yellowcake is used in the preparation of uranium fuel for

nuclear reactor A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat fr ...

s, for which it is smelted into purified UO₂ for use in fuel rods for pressurized heavy-water reactors and other systems that use natural unenriched uranium. Purified uranium can also be enriched into the isotope U-235. In this process, the uranium oxides are combined with

fluorine Fluorine is a chemical element with the symbol F and atomic number 9. It is the lightest halogen and exists at standard conditions as a highly toxic, pale yellow diatomic gas. As the most electronegative reactive element, it is extremely reactiv ...

to form uranium hexafluoride gas (UF₆). Next, the gas undergoes

isotope separation Isotope separation is the process of concentrating specific isotopes of a chemical element by removing other isotopes. The use of the nuclides produced is varied. The largest variety is used in research (e.g. in chemistry where atoms of "marker" ...

through the process of gaseous diffusion, or in a

gas centrifuge A gas centrifuge is a device that performs isotope separation of gases. A centrifuge relies on the principles of centrifugal force accelerating molecules so that particles of different masses are physically separated in a gradient along the radiu ...

. This can produce low-enriched uranium containing up to 20% U-235 that is suitable for use in most large civilian electric-power reactors. With further processing, one obtains

highly enriched uranium Enriched uranium is a type of uranium in which the percent composition of uranium-235 (written 235U) has been increased through the process of isotope separation. Naturally occurring uranium is composed of three major isotopes: uranium-238 (238U ...

, containing 20% or more U-235, that is suitable for use in compact nuclear reactors—usually used to power naval warships and

submarine A submarine (or sub) is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. The term is also sometimes used historically or colloquially to refer to remotely op ...

s. Further processing can yield weapons-grade uranium with U-235 levels usually above 90%, suitable for

nuclear weapon A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions ( thermonuclear bomb), producing a nuclear explosion. Both bomb ...

Radioactivity and safety

The uranium in yellowcake is almost exclusively (>99%) U-238, with very low radioactivity. U-238 has an extremely long

half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ...

, over 4 billion years, meaning that it emits radiation at a slow rate. This stage of processing is before the more radioactive U-235 is concentrated, so by definition, this stage of uranium has the same radioactivity as it did in nature when it was underground, as the proportions of isotopes are at their native relative concentration. Yellowcake is hazardous when inhaled.

References

{{reflist Uranium compounds Oxides Nuclear materials

Overview

Further processing

Radioactivity and safety

See also

References