Editing Actinide (section)

== Extraction ==
[[File:MonaziteUSGOV.jpg|thumb|upright=1.2|[[Monazite]]: a major thorium mineral]]

Owing to the low abundance of actinides, their extraction is a complex, multistep process. [[Fluoride]]s of actinides are usually used because they are insoluble in water and can be easily separated with [[redox]] reactions. Fluorides are reduced with [[calcium]], [[magnesium]] or [[barium]]:<ref name=g215>Golub, pp. 215–217</ref>
: <math chem>\begin{array}{l}{}\\
\ce{2AmF3{} + 3Ba ->[\ce{1150-1350^\circ C}] 3BaF2{} + 2Am}\\
\ce{PuF4{} + 2Ba ->[\ce{1200^\circ C}] 2BaF2{} + Pu}\\
\ce{UF4{} + 2Mg ->[\ce{> 500^\circ C}] U{} + 2MgF2}\\{}
\end{array}</math>

Among the actinides, thorium and uranium are the easiest to isolate. Thorium is extracted mostly from [[monazite]]: thorium [[pyrophosphate]] (ThP<sub>2</sub>O<sub>7</sub>) is reacted with [[nitric acid]], and the produced [[thorium nitrate]] treated with [[tributyl phosphate]]. [[Rare earth element|Rare-earth]] impurities are separated by increasing the [[pH]] in sulfate solution.<ref name=g215 />

In another extraction method, monazite is decomposed with a 45% aqueous solution of [[sodium hydroxide]] at 140&nbsp;°C. Mixed metal hydroxides are extracted first, filtered at 80&nbsp;°C, washed with water and dissolved with concentrated [[hydrochloric acid]]. Next, the acidic solution is neutralized with hydroxides to pH = 5.8 that results in precipitation of [[thorium hydroxide]] (Th(OH)<sub>4</sub>) contaminated with ~3% of rare-earth hydroxides; the rest of rare-earth hydroxides remains in solution. Thorium hydroxide is dissolved in an inorganic acid and then purified from the [[rare earth element]]s. An efficient method is the dissolution of thorium hydroxide in nitric acid, because the resulting solution can be purified by [[Liquid-liquid extraction|extraction]] with organic solvents:<ref name=g215 />

[[File:Plutonium and uranium extraction from nuclear fuel-eng.svg|thumb|right|upright=1.6|Separation of uranium and plutonium from [[spent nuclear fuel]] using the [[PUREX]] process<ref>Greenwood, pp. 1255, 1261</ref>]]

:Th(OH)<sub>4</sub> + 4 HNO<sub>3</sub> → Th(NO<sub>3</sub>)<sub>4</sub> + 4 H<sub>2</sub>O

Metallic thorium is separated from the anhydrous [[Thorium dioxide|oxide]], [[Thorium(IV) chloride|chloride]] or [[Thorium(IV) fluoride|fluoride]] by reacting it with calcium in an inert atmosphere:<ref name=g1255 />

:ThO<sub>2</sub> + 2 Ca → 2 CaO + Th

Sometimes thorium is extracted by [[electrolysis]] of a fluoride in a mixture of sodium and potassium chloride at 700–800&nbsp;°C in a [[graphite]] crucible. Highly pure thorium can be extracted from its iodide with the [[crystal bar process]].<ref>{{cite journal|doi=10.1002/zaac.19251480133|title=Darstellung von reinem Titanium-, Zirkonium-, Hafnium- und Thoriummetall|author=A. E. van Arkel|author2=de Boer, J. H.|volume=148|issue=1|pages=345–350|year=1925|journal=Zeitschrift für Anorganische und Allgemeine Chemie|language=de}}</ref>

Uranium is extracted from its ores in various ways. In one method, the ore is burned and then reacted with nitric acid to convert uranium into a dissolved state. Treating the solution with a solution of tributyl phosphate (TBP) in [[kerosene]] transforms uranium into an organic form UO<sub>2</sub>(NO<sub>3</sub>)<sub>2</sub>(TBP)<sub>2</sub>. The insoluble impurities are filtered and the uranium is extracted by reaction with hydroxides as [[Ammonium diuranate|(NH<sub>4</sub>)<sub>2</sub>U<sub>2</sub>O<sub>7</sub>]] or with [[hydrogen peroxide]] as [[Uranyl peroxide|UO<sub>4</sub>·2H<sub>2</sub>O]].<ref name=g215 />

When the uranium ore is rich in such minerals as [[dolomite (mineral)|dolomite]], [[magnesite]], etc., those minerals consume much acid. In this case, the carbonate method is used for uranium extraction. Its main component is an aqueous solution of [[sodium carbonate]], which converts uranium into a complex [UO<sub>2</sub>(CO<sub>3</sub>)<sub>3</sub>]<sup>4−</sup>, which is stable in aqueous solutions at low concentrations of hydroxide ions. The advantages of the sodium carbonate method are that the chemicals have low [[Corrosion|corrosivity]] (compared to nitrates) and that most non-uranium metals precipitate from the solution. The disadvantage is that tetravalent uranium compounds precipitate as well. Therefore, the uranium ore is treated with sodium carbonate at elevated temperature and under oxygen pressure:
:2 UO<sub>2</sub> + O<sub>2</sub> + 6 {{chem|CO|3|2-}} → 2 [UO<sub>2</sub>(CO<sub>3</sub>)<sub>3</sub>]<sup>4−</sup>
This equation suggests that the best solvent for the [[uranyl carbonate]] processing is a mixture of carbonate with bicarbonate. At high pH, this results in precipitation of [[diuranate]], which is treated with [[hydrogen]] in the presence of nickel yielding an insoluble uranium tetracarbonate.<ref name=g215 />

Another separation method uses polymeric resins as a [[polyelectrolyte]]. Ion exchange processes in the resins result in separation of uranium. Uranium from resins is washed with a solution of [[ammonium nitrate]] or nitric acid that yields [[uranyl nitrate]], UO<sub>2</sub>(NO<sub>3</sub>)<sub>2</sub>·6H<sub>2</sub>O. When heated, it turns into [[Uranium trioxide|UO<sub>3</sub>]], which is converted to [[uranium dioxide|UO<sub>2</sub>]] with hydrogen:
: UO<sub>3</sub> + H<sub>2</sub> → UO<sub>2</sub> + H<sub>2</sub>O
Reacting uranium dioxide with [[hydrofluoric acid]] changes it to [[uranium tetrafluoride]], which yields uranium metal upon reaction with magnesium metal:<ref name=g1255 />
: 4 HF + UO<sub>2</sub> → UF<sub>4</sub> + 2 H<sub>2</sub>O

To extract plutonium, neutron-irradiated uranium is dissolved in nitric acid, and a reducing agent ([[Iron(II) sulfate|FeSO<sub>4</sub>]], or [[hydrogen peroxide|H<sub>2</sub>O<sub>2</sub>]]) is added to the resulting solution. This addition changes the oxidation state of plutonium from +6 to +4, while uranium remains in the form of uranyl nitrate (UO<sub>2</sub>(NO<sub>3</sub>)<sub>2</sub>). The solution is treated with a reducing agent and neutralized with [[ammonium carbonate]] to pH = 8 that results in precipitation of Pu<sup>4+</sup> compounds.<ref name=g215 />

In another method, Pu<sup>4+</sup> and {{chem|UO|2|2+}} are first extracted with tributyl phosphate, then reacted with [[hydrazine]] washing out the recovered plutonium.<ref name=g215 />

The major difficulty in separation of actinium is the similarity of its properties with those of lanthanum. Thus actinium is either synthesized in nuclear reactions from isotopes of radium or separated using ion-exchange procedures.<ref name="Himiya aktiniya" />