Editing Erbium (section)

==Production==
Crushed minerals are attacked by hydrochloric or [[sulfuric acid]] that transforms insoluble rare-earth oxides into soluble chlorides or sulfates. The acidic filtrates are partially neutralized with caustic soda (sodium hydroxide) to pH 3–4. [[Thorium]] precipitates out of solution as hydroxide and is removed. After that the solution is treated with [[ammonium oxalate]] to convert rare earths into their insoluble [[oxalate]]s. The oxalates are converted to oxides by annealing. The oxides are dissolved in [[nitric acid]] that excludes one of the main components, [[cerium]], whose oxide is insoluble in HNO<sub>3</sub>. The solution is treated with [[magnesium nitrate]] to produce a crystallized mixture of [[double salt]]s of rare-earth metals. The salts are separated by [[ion exchange]]. In this process, rare-earth ions are sorbed onto suitable ion-exchange resin by exchange with hydrogen, ammonium or cupric ions present in the resin. The rare earth ions are then selectively washed out by suitable complexing agent.<ref name="patnaik" /> Erbium metal is obtained from its oxide or salts by heating with [[calcium]] at {{val|1450|u=°C}} under argon atmosphere.<ref name="patnaik" />