Fluoride volatility is the tendency of highly fluorinated molecules to vaporize at comparatively low temperatures. Heptafluorides, hexafluorides and pentafluorides have much lower boiling points than the lower- valence fluorides. Most difluorides and trifluorides have high boiling points, while most

tetrafluoride A tetrafluoride is a chemical compound with four fluorines in its formula. List of tetrafluorides *Argon tetrafluoride, (hypothetical) *Berkelium tetrafluoride *Carbon tetrafluoride (tetrafluoromethane) *Diboron tetrafluoride, a colorless gas *Din ...

s and monofluorides fall in between. The term "fluoride volatility" is

jargon Jargon is the specialized terminology associated with a particular field or area of activity. Jargon is normally employed in a particular communicative context and may not be well understood outside that context. The context is usually a partic ...

used particularly in the context of separation of radionuclides.

Volatility and valence

Valences for the majority of elements are based on the highest known fluoride. Roughly, fluoride volatility can be used to remove elements with a valence of 5 or greater:

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 ...

neptunium Neptunium is a chemical element with the symbol Np and atomic number 93. A radioactive actinide metal, neptunium is the first transuranic element. Its position in the periodic table just after uranium, named after the planet Uranus, led to it bein ...

plutonium Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibi ...

metalloids A metalloid is a type of chemical element which has a preponderance of properties in between, or that are a mixture of, those of metals and nonmetals. There is no standard definition of a metalloid and no complete agreement on which elements are ...

(

tellurium Tellurium is a chemical element with the symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionall ...

antimony Antimony is a chemical element with the symbol Sb (from la, stibium) and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient t ...

nonmetals In chemistry, a nonmetal is a chemical element that generally lacks a predominance of metallic properties; they range from colorless gases (like hydrogen) to shiny solids (like carbon, as graphite). The electrons in nonmetals behave differentl ...

(

selenium Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, ...

halogens The halogens () are a group in the periodic table consisting of five or six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). In the modern IUPAC nomenclature, this group i ...

( iodine,

bromine Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table ( halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simi ...

), and the middle

transition metal In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that ca ...

s ( niobium, molybdenum,

technetium Technetium is a chemical element with the symbol Tc and atomic number 43. It is the lightest element whose isotopes are all radioactive. All available technetium is produced as a synthetic element. Naturally occurring technetium is a spontaneous ...

ruthenium Ruthenium is a chemical element with the symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to most other chemical ...

, and possibly

rhodium Rhodium is a chemical element with the symbol Rh and atomic number 45. It is a very rare, silvery-white, hard, corrosion-resistant transition metal. It is a noble metal and a member of the platinum group. It has only one naturally occurring i ...

). This fraction includes the actinides most easily reusable as nuclear fuel in a

thermal reactor A thermal-neutron reactor is a nuclear reactor that uses slow or thermal neutrons. ("Thermal" does not mean hot in an absolute sense, but means in thermal equilibrium with the medium it is interacting with, the reactor's fuel, moderator and struct ...

, and the two long-lived fission products best suited to disposal by transmutation,

Tc-99 Technetium-99 (99Tc) is an isotope of technetium which decays with a half-life of 211,000 years to stable ruthenium-99, emitting beta particles, but no gamma rays. It is the most significant long-lived fission product of uranium fission, produ ...

and I-129, as well as Se-79.

Noble gases The noble gases (historically also the inert gases; sometimes referred to as aerogens) make up a class of chemical elements with similar properties; under standard conditions, they are all odorless, colorless, monatomic gases with very low ch ...

(

xenon Xenon is a chemical element with the symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...

krypton Krypton (from grc, κρυπτός, translit=kryptos 'the hidden one') is a chemical element with the symbol Kr and atomic number 36. It is a colorless, odorless, tasteless noble gas that occurs in trace amounts in the atmosphere and is often ...

) are volatile even without fluoridation, and will not condense except at much lower temperatures. Left behind are

alkali metals The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K),The symbols Na and K for sodium and potassium are derived from their Latin names, ''natrium'' and ''kalium''; these are still the origins of the names ...

( caesium, rubidium),

alkaline earth metals The alkaline earth metals are six chemical elements in group 2 of the periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).. The elements have very similar properties: they are all ...

( strontium, barium),

lanthanides The lanthanide () or lanthanoid () series of chemical elements comprises the 15 metallic chemical elements with atomic numbers 57–71, from lanthanum through lutetium. These elements, along with the chemically similar elements scandium and ytt ...

, the remaining

actinides The actinide () or actinoid () series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium. The actinide series derives its name from the first element in the series, actinium. The inform ...

( americium, curium), remaining

s (

yttrium Yttrium is a chemical element with the symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a " rare-earth element". Yttrium is almost always found in co ...

zirconium Zirconium is a chemical element with the symbol Zr and atomic number 40. The name ''zirconium'' is taken from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian '' zargun'' (zircon; ''zar-gun'' ...

palladium Palladium is a chemical element with the symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1803 by the English chemist William Hyde Wollaston. He named it after the asteroid Pallas, which was itself na ...

silver Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...

) and

post-transition metal The metallic elements in the periodic table located between the transition metals and the chemically weak nonmetallic metalloids have received many names in the literature, such as ''post-transition metals'', ''poor metals'', ''other metals'', ...

s (

tin Tin is a chemical element with the symbol Sn (from la, stannum) and atomic number 50. Tin is a silvery-coloured metal. Tin is soft enough to be cut with little force and a bar of tin can be bent by hand with little effort. When bent, t ...

indium Indium is a chemical element with the symbol In and atomic number 49. Indium is the softest metal that is not an alkali metal. It is a silvery-white metal that resembles tin in appearance. It is a post-transition metal that makes up 0.21 parts ...

cadmium Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Like zinc, it demonstrates oxidation state +2 in most of ...

). This fraction contains the fission products that are radiation hazards on a scale of decades ( Cs-137, Sr-90, Sm-151), the four remaining long-lived fission products Cs-135,

Zr-93 Naturally occurring zirconium (40Zr) is composed of four stable isotopes (of which one observationally stable, may in the future be found radioactive), and one very long-lived radioisotope (96Zr), a primordial nuclide that decays via double beta d ...

, Pd-107, Sn-126 of which only the last emits strong radiation, most of the

neutron poison In applications such as nuclear reactors, a neutron poison (also called a neutron absorber or a nuclear poison) is a substance with a large neutron absorption cross-section. In such applications, absorbing neutrons is normally an undesirable eff ...

s, and the higher actinides ( americium, curium,

californium Californium is a radioactive chemical element with the symbol Cf and atomic number 98. The element was first synthesized in 1950 at Lawrence Berkeley National Laboratory (then the University of California Radiation Laboratory), by bombarding ...

) that are radiation hazards on a scale of hundreds or thousands of years and are difficult to work with because of gamma radiation but are fissionable in a

fast reactor A fast-neutron reactor (FNR) or fast-spectrum reactor or simply a fast reactor is a category of nuclear reactor in which the fission chain reaction is sustained by fast neutrons (carrying energies above 1 MeV or greater, on average), as oppose ...

Reprocessing methods

Uranium oxide Uranium oxide is an oxide of the element uranium. The metal uranium forms several oxides: * Uranium dioxide or uranium(IV) oxide (UO2, the mineral uraninite or pitchblende) * Diuranium pentoxide or uranium(V) oxide (U2O5) * Uranium trioxide o ...

s react with fluorine to form gaseous

uranium hexafluoride Uranium hexafluoride (), (sometimes called "hex") is an inorganic compound with the formula UF6. Uranium hexafluoride is a volatile white solid that reacts with water, releasing corrosive hydrofluoric acid. The compound reacts mildly with alumin ...

, most of the

reacts to form gaseous plutonium hexafluoride, a majority of fission products (especially electropositive elements: lanthanides, strontium, barium,

, caesium) form nonvolatile fluorides. Few metals in the fission products (the

s niobium,

, molybdenum, and the halogen iodine) form volatile (boiling point <200 °C) fluorides that accompany the uranium and plutonium hexafluorides, together with

inert gas An inert gas is a gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds. The noble gases often do not react with many substances and were historically referred to ...

es.

Distillation Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the heat ...

is then used to separate the uranium hexafluoride from the mixture. The nonvolatile alkaline fission products and

minor actinides The minor actinides are the actinide elements in used nuclear fuel other than uranium and plutonium, which are termed the major actinides. The minor actinides include neptunium (element 93), americium (element 95), curium (element 96), berkeliu ...

is most suitable for further processing with 'dry'

electrochemical Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference, as a measurable and quantitative phenomenon, and identifiable chemical change, with the potential difference as an outc ...

processing ( pyrochemical) non-aqueous methods. The lanthanide fluorides are difficult to dissolve in the

nitric acid Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...

used for aqueous reprocessing methods, such as PUREX, DIAMEX and

SANEX Sanex is a brand of personal care products owned by Colgate-Palmolive. It is sold in European countries (including United Kingdom, Netherlands, Belgium, France, Spain, Portugal, Denmark, Greece, Poland, Norway and Croatia) and South Africa. In ...

, which use

solvent extraction A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...

. Fluoride volatility is only one of several pyrochemical processes designed to reprocess used nuclear fuel. Th
Řež nuclear research institute
at

Řež Řež () is a village (a part of Husinec municipality) in Central Bohemian Region of the Czech Republic. It is located in valley of the Vltava River 11 km northwest from centre of Prague. According to the 2001 census the population was 722. ...

in the

Czech Republic The Czech Republic, or simply Czechia, is a landlocked country in Central Europe. Historically known as Bohemia, it is bordered by Austria to the south, Germany to the west, Poland to the northeast, and Slovakia to the southeast. The ...

tested screw dosers that fed ground uranium oxide (simulating used fuel pellets) into a fluorinator where the particles were burned in fluorine gas to form

. Hitachi has developed a technology, called FLUOREX, which combines fluoride volatility, to extract uranium, with more traditional solvent extraction (PUREX), to extract plutonium and other transuranics]. The FLUOREX-based fuel cycle is intended for use with the

Reduced moderation water reactor The Reduced-Moderation Water Reactor (RMWR), also referred to as the Resource-renewable BWR, is a proposed type of light water reactor, light water moderated nuclear power reactor, featuring some characteristics of a fast neutron reactor, thereby c ...

Table of relevant properties

Notes

*Missing top fluorides: **PrF₄ (because it decomposes at 90 °C) **TbF₄ (because it decomposes at 300 °C) **CeF₄ (because it decomposes at 600 °C) *Without stable fluorides: Kr, Xe, PdPrecious metal refining with fluorine gas – Patent 5076839
Freepatentsonline.com. Retrieved on 2010-11-14.

References

External links

Study of Electrochemical Processes for Separation of the Actinides and Lanthanides in Molten Fluoride Media
( PDF) *{{cite web , url=http://www.fjfi.cvut.cz/con_adtt99/papers/P-g5.pdf , title=Separation and purification of UF₆ from volatile fluorides by rectification , archiveurl=https://web.archive.org/web/20050113100054/http://www.fjfi.cvut.cz/con_adtt99/papers/P-g5.pdf , archivedate=13 January 2005
Low-pressure distillation of a portion of the fuel carrier salt from the Molten Salt Reactor Experiment
(PDF)
Use of the Fluoride Volatility Process to Extract Technetium from Transmuted Spent Nuclear Fuel
(PDF)
A Peer Review of the Strategy for Characterizing Transuranics and Technetium Contamination in Depleted Uranium Hexafluoride Tails Cylinders
(PDF)
PHYSICAL CONSTANTS OF INORGANIC COMPOUNDS
(PDF) Nuclear reprocessing Nuclear chemistry Fluorides